xref: /netbsd-src/usr.bin/make/var.c (revision a8c74629f602faa0ccf8a463757d7baf858bbf3a)

/*	$NetBSD: var.c,v 1.688 2020/11/16 21:39:22 rillig Exp $	*/

/*
 * Copyright (c) 1988, 1989, 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Adam de Boor.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Copyright (c) 1989 by Berkeley Softworks
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Adam de Boor.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Handling of variables and the expressions formed from them.
 *
 * Variables are set using lines of the form VAR=value.  Both the variable
 * name and the value can contain references to other variables, by using
 * expressions like ${VAR}, ${VAR:Modifiers}, ${${VARNAME}} or ${VAR:${MODS}}.
 *
 * Interface:
 *	Var_Init	Initialize this module.
 *
 *	Var_End		Clean up the module.
 *
 *	Var_Set		Set the value of the variable, creating it if
 *			necessary.
 *
 *	Var_Append	Append more characters to the variable, creating it if
 *			necessary. A space is placed between the old value and
 *			the new one.
 *
 *	Var_Exists	See if a variable exists.
 *
 *	Var_Value	Return the unexpanded value of a variable, or NULL if
 *			the variable is undefined.
 *
 *	Var_Subst	Substitute all variable expressions in a string.
 *
 *	Var_Parse	Parse a variable expression such as ${VAR:Mpattern}.
 *
 *	Var_Delete	Delete a variable.
 *
 *	Var_ExportVars	Export some or even all variables to the environment
 *			of this process and its child processes.
 *
 *	Var_Export	Export the variable to the environment of this process
 *			and its child processes.
 *
 *	Var_UnExport	Don't export the variable anymore.
 *
 * Debugging:
 *	Var_Stats	Print out hashing statistics if in -dh mode.
 *
 *	Var_Dump	Print out all variables defined in the given context.
 *
 * XXX: There's a lot of duplication in these functions.
 */

#include <sys/stat.h>
#ifndef NO_REGEX
#include <sys/types.h>
#include <regex.h>
#endif
#include <errno.h>
#include <inttypes.h>
#include <limits.h>
#include <time.h>

#include "make.h"
#include "dir.h"
#include "job.h"
#include "metachar.h"

/*	"@(#)var.c	8.3 (Berkeley) 3/19/94" */
MAKE_RCSID("$NetBSD: var.c,v 1.688 2020/11/16 21:39:22 rillig Exp $");

#define VAR_DEBUG1(fmt, arg1) DEBUG1(VAR, fmt, arg1)
#define VAR_DEBUG2(fmt, arg1, arg2) DEBUG2(VAR, fmt, arg1, arg2)
#define VAR_DEBUG3(fmt, arg1, arg2, arg3) DEBUG3(VAR, fmt, arg1, arg2, arg3)
#define VAR_DEBUG4(fmt, arg1, arg2, arg3, arg4) DEBUG4(VAR, fmt, arg1, arg2, arg3, arg4)

ENUM_FLAGS_RTTI_3(VarEvalFlags,
		  VARE_UNDEFERR, VARE_WANTRES, VARE_KEEP_DOLLAR);

/*
 * This lets us tell if we have replaced the original environ
 * (which we cannot free).
 */
char **savedEnv = NULL;

/* Special return value for Var_Parse, indicating a parse error.  It may be
 * caused by an undefined variable, a syntax error in a modifier or
 * something entirely different. */
char var_Error[] = "";

/* Special return value for Var_Parse, indicating an undefined variable in
 * a case where VARE_UNDEFERR is not set.  This undefined variable is
 * typically a dynamic variable such as ${.TARGET}, whose expansion needs to
 * be deferred until it is defined in an actual target. */
static char varUndefined[] = "";

/*
 * Traditionally this make consumed $$ during := like any other expansion.
 * Other make's do not, and this make follows straight since 2016-01-09.
 *
 * This knob allows controlling the behavior.
 * FALSE to consume $$ during := assignment.
 * TRUE to preserve $$ during := assignment.
 */
#define MAKE_SAVE_DOLLARS ".MAKE.SAVE_DOLLARS"
static Boolean save_dollars = TRUE;

/*
 * Internally, variables are contained in four different contexts.
 *	1) the environment. They cannot be changed. If an environment
 *	   variable is appended to, the result is placed in the global
 *	   context.
 *	2) the global context. Variables set in the makefiles are located
 *	   here.
 *	3) the command-line context. All variables set on the command line
 *	   are placed in this context.
 *	4) the local context. Each target has associated with it a context
 *	   list. On this list are located the structures describing such
 *	   local variables as $(@) and $(*)
 * The four contexts are searched in the reverse order from which they are
 * listed (but see opts.checkEnvFirst).
 */
GNode          *VAR_INTERNAL;	/* variables from make itself */
GNode          *VAR_GLOBAL;	/* variables from the makefile */
GNode          *VAR_CMDLINE;	/* variables defined on the command-line */

typedef enum VarFlags {

    /* The variable's value is currently being used by Var_Parse or Var_Subst.
     * This marker is used to avoid endless recursion. */
    VAR_IN_USE = 0x01,

    /* The variable comes from the environment.
     * These variables are not registered in any GNode, therefore they must
     * be freed as soon as they are not used anymore. */
    VAR_FROM_ENV = 0x02,

    /* The variable is exported to the environment, to be used by child
     * processes. */
    VAR_EXPORTED = 0x10,

    /* At the point where this variable was exported, it contained an
     * unresolved reference to another variable.  Before any child process is
     * started, it needs to be exported again, in the hope that the referenced
     * variable can then be resolved. */
    VAR_REEXPORT = 0x20,

    /* The variable came from the command line. */
    VAR_FROM_CMD = 0x40,

    /* The variable value cannot be changed anymore, and the variable cannot
     * be deleted.  Any attempts to do so are ignored. */
    VAR_READONLY = 0x80
} VarFlags;

ENUM_FLAGS_RTTI_6(VarFlags,
		  VAR_IN_USE, VAR_FROM_ENV,
		  VAR_EXPORTED, VAR_REEXPORT, VAR_FROM_CMD, VAR_READONLY);

/* Variables are defined using one of the VAR=value assignments.  Their
 * value can be queried by expressions such as $V, ${VAR}, or with modifiers
 * such as ${VAR:S,from,to,g:Q}.
 *
 * There are 3 kinds of variables: context variables, environment variables,
 * undefined variables.
 *
 * Context variables are stored in a GNode.context.  The only way to undefine
 * a context variable is using the .undef directive.  In particular, it must
 * not be possible to undefine a variable during the evaluation of an
 * expression, or Var.name might point nowhere.
 *
 * Environment variables are temporary.  They are returned by VarFind, and
 * after using them, they must be freed using VarFreeEnv.
 *
 * Undefined variables occur during evaluation of variable expressions such
 * as ${UNDEF:Ufallback} in Var_Parse and ApplyModifiers.
 */
typedef struct Var {
    /* The name of the variable, once set, doesn't change anymore.
     * For context variables, it aliases the corresponding HashEntry name.
     * For environment and undefined variables, it is allocated. */
    const char *name;
    void *name_freeIt;

    Buffer	  val;		/* its value */
    VarFlags	  flags;	/* miscellaneous status flags */
} Var;

/*
 * Exporting vars is expensive so skip it if we can
 */
typedef enum VarExportedMode {
    VAR_EXPORTED_NONE,
    VAR_EXPORTED_SOME,
    VAR_EXPORTED_ALL
} VarExportedMode;

static VarExportedMode var_exportedVars = VAR_EXPORTED_NONE;

typedef enum VarExportFlags {
    VAR_EXPORT_NORMAL = 0,
    /*
     * We pass this to Var_Export when doing the initial export
     * or after updating an exported var.
     */
    VAR_EXPORT_PARENT	= 0x01,
    /*
     * We pass this to Var_Export1 to tell it to leave the value alone.
     */
    VAR_EXPORT_LITERAL	= 0x02
} VarExportFlags;

/* Flags for pattern matching in the :S and :C modifiers */
typedef enum VarPatternFlags {
    VARP_SUB_GLOBAL	= 0x01,	/* Replace as often as possible ('g') */
    VARP_SUB_ONE	= 0x02,	/* Replace only once ('1') */
    VARP_ANCHOR_START	= 0x04,	/* Match at start of word ('^') */
    VARP_ANCHOR_END	= 0x08	/* Match at end of word ('$') */
} VarPatternFlags;

static Var *
VarNew(const char *name, void *name_freeIt, const char *value, VarFlags flags)
{
    size_t value_len = strlen(value);
    Var *var = bmake_malloc(sizeof *var);
    var->name = name;
    var->name_freeIt = name_freeIt;
    Buf_InitSize(&var->val, value_len + 1);
    Buf_AddBytes(&var->val, value, value_len);
    var->flags = flags;
    return var;
}

static const char *
CanonicalVarname(const char *name)
{
    if (*name == '.' && ch_isupper(name[1])) {
	switch (name[1]) {
	case 'A':
	    if (strcmp(name, ".ALLSRC") == 0)
		name = ALLSRC;
	    if (strcmp(name, ".ARCHIVE") == 0)
		name = ARCHIVE;
	    break;
	case 'I':
	    if (strcmp(name, ".IMPSRC") == 0)
		name = IMPSRC;
	    break;
	case 'M':
	    if (strcmp(name, ".MEMBER") == 0)
		name = MEMBER;
	    break;
	case 'O':
	    if (strcmp(name, ".OODATE") == 0)
		name = OODATE;
	    break;
	case 'P':
	    if (strcmp(name, ".PREFIX") == 0)
		name = PREFIX;
	    break;
	case 'S':
	    if (strcmp(name, ".SHELL") == 0) {
		if (!shellPath)
		    Shell_Init();
	    }
	    break;
	case 'T':
	    if (strcmp(name, ".TARGET") == 0)
		name = TARGET;
	    break;
	}
    }

    /* GNU make has an additional alias $^ == ${.ALLSRC}. */

    return name;
}

static Var *
GNode_FindVar(GNode *ctxt, const char *varname, unsigned int hash)
{
    return HashTable_FindValueHash(&ctxt->context, varname, hash);
}

/* Find the variable in the context, and maybe in other contexts as well.
 *
 * Input:
 *	name		name to find, is not expanded any further
 *	ctxt		context in which to look first
 *	elsewhere	TRUE to look in other contexts as well
 *
 * Results:
 *	The found variable, or NULL if the variable does not exist.
 *	If the variable is an environment variable, it must be freed using
 *	VarFreeEnv after use.
 */
static Var *
VarFind(const char *name, GNode *ctxt, Boolean elsewhere)
{
    Var *var;
    unsigned int nameHash;

    /*
     * If the variable name begins with a '.', it could very well be one of
     * the local ones.  We check the name against all the local variables
     * and substitute the short version in for 'name' if it matches one of
     * them.
     */
    name = CanonicalVarname(name);
    nameHash = Hash_Hash(name);

    /* First look for the variable in the given context. */
    var = GNode_FindVar(ctxt, name, nameHash);
    if (!elsewhere)
	return var;

    /* The variable was not found in the given context.  Now look for it in
     * the other contexts as well. */
    if (var == NULL && ctxt != VAR_CMDLINE)
	var = GNode_FindVar(VAR_CMDLINE, name, nameHash);

    if (!opts.checkEnvFirst && var == NULL && ctxt != VAR_GLOBAL) {
	var = GNode_FindVar(VAR_GLOBAL, name, nameHash);
	if (var == NULL && ctxt != VAR_INTERNAL) {
	    /* VAR_INTERNAL is subordinate to VAR_GLOBAL */
	    var = GNode_FindVar(VAR_INTERNAL, name, nameHash);
	}
    }

    if (var == NULL) {
	char *env;

	if ((env = getenv(name)) != NULL) {
	    char *varname = bmake_strdup(name);
	    return VarNew(varname, varname, env, VAR_FROM_ENV);
	}

	if (opts.checkEnvFirst && ctxt != VAR_GLOBAL) {
	    var = GNode_FindVar(VAR_GLOBAL, name, nameHash);
	    if (var == NULL && ctxt != VAR_INTERNAL)
		var = GNode_FindVar(VAR_INTERNAL, name, nameHash);
	    return var;
	}

	return NULL;
    }

    return var;
}

/* If the variable is an environment variable, free it.
 *
 * Input:
 *	v		the variable
 *	freeValue	true if the variable value should be freed as well
 *
 * Results:
 *	TRUE if it is an environment variable, FALSE otherwise.
 */
static Boolean
VarFreeEnv(Var *v, Boolean freeValue)
{
    if (!(v->flags & VAR_FROM_ENV))
	return FALSE;

    free(v->name_freeIt);
    Buf_Destroy(&v->val, freeValue);
    free(v);
    return TRUE;
}

/* Add a new variable of the given name and value to the given context.
 * The name and val arguments are duplicated so they may safely be freed. */
static void
VarAdd(const char *name, const char *val, GNode *ctxt, VarSetFlags flags)
{
    HashEntry *he = HashTable_CreateEntry(&ctxt->context, name, NULL);
    Var *v = VarNew(he->key /* aliased */, NULL, val,
		    flags & VAR_SET_READONLY ? VAR_READONLY : 0);
    HashEntry_Set(he, v);
    if (!(ctxt->flags & INTERNAL)) {
	VAR_DEBUG3("%s:%s = %s\n", ctxt->name, name, val);
    }
}

/* Remove a variable from a context, freeing all related memory as well.
 * The variable name is expanded once. */
void
Var_Delete(const char *name, GNode *ctxt)
{
    char *name_freeIt = NULL;
    HashEntry *he;

    if (strchr(name, '$') != NULL) {
	(void)Var_Subst(name, VAR_GLOBAL, VARE_WANTRES, &name_freeIt);
	/* TODO: handle errors */
	name = name_freeIt;
    }
    he = HashTable_FindEntry(&ctxt->context, name);
    VAR_DEBUG3("%s:delete %s%s\n",
	       ctxt->name, name, he != NULL ? "" : " (not found)");
    free(name_freeIt);

    if (he != NULL) {
	Var *v = HashEntry_Get(he);
	if (v->flags & VAR_EXPORTED)
	    unsetenv(v->name);
	if (strcmp(v->name, MAKE_EXPORTED) == 0)
	    var_exportedVars = VAR_EXPORTED_NONE;
	assert(v->name_freeIt == NULL);
	HashTable_DeleteEntry(&ctxt->context, he);
	Buf_Destroy(&v->val, TRUE);
	free(v);
    }
}

static Boolean
MayExport(const char *name)
{
    if (name[0] == '.')
	return FALSE;		/* skip internals */
    if (name[0] == '-')
	return FALSE;		/* skip misnamed variables */
    if (name[1] == '\0') {
	/*
	 * A single char.
	 * If it is one of the vars that should only appear in
	 * local context, skip it, else we can get Var_Subst
	 * into a loop.
	 */
	switch (name[0]) {
	case '@':
	case '%':
	case '*':
	case '!':
	    return FALSE;
	}
    }
    return TRUE;
}

/*
 * Export a single variable.
 * We ignore make internal variables (those which start with '.').
 * Also we jump through some hoops to avoid calling setenv
 * more than necessary since it can leak.
 * We only manipulate flags of vars if 'parent' is set.
 */
static Boolean
Var_Export1(const char *name, VarExportFlags flags)
{
    VarExportFlags parent = flags & VAR_EXPORT_PARENT;
    Var *v;
    char *val;

    if (!MayExport(name))
	return FALSE;

    v = VarFind(name, VAR_GLOBAL, FALSE);
    if (v == NULL)
	return FALSE;

    if (!parent && (v->flags & VAR_EXPORTED) && !(v->flags & VAR_REEXPORT))
	return FALSE;		/* nothing to do */

    val = Buf_GetAll(&v->val, NULL);
    if (!(flags & VAR_EXPORT_LITERAL) && strchr(val, '$') != NULL) {
	char *expr;

	if (parent) {
	    /*
	     * Flag the variable as something we need to re-export.
	     * No point actually exporting it now though,
	     * the child process can do it at the last minute.
	     */
	    v->flags |= VAR_EXPORTED | VAR_REEXPORT;
	    return TRUE;
	}
	if (v->flags & VAR_IN_USE) {
	    /*
	     * We recursed while exporting in a child.
	     * This isn't going to end well, just skip it.
	     */
	    return FALSE;
	}

	/* XXX: name is injected without escaping it */
	expr = str_concat3("${", name, "}");
	(void)Var_Subst(expr, VAR_GLOBAL, VARE_WANTRES, &val);
	/* TODO: handle errors */
	setenv(name, val, 1);
	free(val);
	free(expr);
    } else {
	if (parent)
	    v->flags &= ~(unsigned)VAR_REEXPORT;	/* once will do */
	if (parent || !(v->flags & VAR_EXPORTED))
	    setenv(name, val, 1);
    }

    /*
     * This is so Var_Set knows to call Var_Export again...
     */
    if (parent) {
	v->flags |= VAR_EXPORTED;
    }
    return TRUE;
}

/*
 * This gets called from our child processes.
 */
void
Var_ExportVars(void)
{
    char *val;

    /*
     * Several make's support this sort of mechanism for tracking
     * recursion - but each uses a different name.
     * We allow the makefiles to update MAKELEVEL and ensure
     * children see a correctly incremented value.
     */
    char tmp[BUFSIZ];
    snprintf(tmp, sizeof tmp, "%d", makelevel + 1);
    setenv(MAKE_LEVEL_ENV, tmp, 1);

    if (var_exportedVars == VAR_EXPORTED_NONE)
	return;

    if (var_exportedVars == VAR_EXPORTED_ALL) {
	HashIter hi;

	/* Ouch! Exporting all variables at once is crazy... */
	HashIter_Init(&hi, &VAR_GLOBAL->context);
	while (HashIter_Next(&hi) != NULL) {
	    Var *var = hi.entry->value;
	    Var_Export1(var->name, VAR_EXPORT_NORMAL);
	}
	return;
    }

    (void)Var_Subst("${" MAKE_EXPORTED ":O:u}", VAR_GLOBAL, VARE_WANTRES, &val);
    /* TODO: handle errors */
    if (*val) {
	Words words = Str_Words(val, FALSE);
	size_t i;

	for (i = 0; i < words.len; i++)
	    Var_Export1(words.words[i], VAR_EXPORT_NORMAL);
	Words_Free(words);
    }
    free(val);
}

/*
 * This is called when .export is seen or .MAKE.EXPORTED is modified.
 *
 * It is also called when any exported variable is modified.
 * XXX: Is it really?
 *
 * str has the format "[-env|-literal] varname...".
 */
void
Var_Export(const char *str, Boolean isExport)
{
    VarExportFlags flags;
    char *val;

    if (isExport && str[0] == '\0') {
	var_exportedVars = VAR_EXPORTED_ALL; /* use with caution! */
	return;
    }

    if (isExport && strncmp(str, "-env", 4) == 0) {
	str += 4;
	flags = 0;
    } else if (isExport && strncmp(str, "-literal", 8) == 0) {
	str += 8;
	flags = VAR_EXPORT_LITERAL;
    } else {
	flags = VAR_EXPORT_PARENT;
    }

    (void)Var_Subst(str, VAR_GLOBAL, VARE_WANTRES, &val);
    /* TODO: handle errors */
    if (val[0] != '\0') {
	Words words = Str_Words(val, FALSE);

	size_t i;
	for (i = 0; i < words.len; i++) {
	    const char *name = words.words[i];
	    if (Var_Export1(name, flags)) {
		if (var_exportedVars == VAR_EXPORTED_NONE)
		    var_exportedVars = VAR_EXPORTED_SOME;
		if (isExport && (flags & VAR_EXPORT_PARENT)) {
		    Var_Append(MAKE_EXPORTED, name, VAR_GLOBAL);
		}
	    }
	}
	Words_Free(words);
    }
    free(val);
}


extern char **environ;

/*
 * This is called when .unexport[-env] is seen.
 *
 * str must have the form "unexport[-env] varname...".
 */
void
Var_UnExport(const char *str)
{
    const char *varnames;
    char *varnames_freeIt;
    Boolean unexport_env;

    varnames = NULL;
    varnames_freeIt = NULL;

    str += strlen("unexport");
    unexport_env = strncmp(str, "-env", 4) == 0;
    if (unexport_env) {
	const char *cp;
	char **newenv;

	cp = getenv(MAKE_LEVEL_ENV);	/* we should preserve this */
	if (environ == savedEnv) {
	    /* we have been here before! */
	    newenv = bmake_realloc(environ, 2 * sizeof(char *));
	} else {
	    if (savedEnv) {
		free(savedEnv);
		savedEnv = NULL;
	    }
	    newenv = bmake_malloc(2 * sizeof(char *));
	}

	/* Note: we cannot safely free() the original environ. */
	environ = savedEnv = newenv;
	newenv[0] = NULL;
	newenv[1] = NULL;
	if (cp && *cp)
	    setenv(MAKE_LEVEL_ENV, cp, 1);
    } else {
	cpp_skip_whitespace(&str);
	if (str[0] != '\0')
	    varnames = str;
    }

    if (varnames == NULL) {
	/* Using .MAKE.EXPORTED */
	(void)Var_Subst("${" MAKE_EXPORTED ":O:u}", VAR_GLOBAL, VARE_WANTRES,
			&varnames_freeIt);
	/* TODO: handle errors */
	varnames = varnames_freeIt;
    }

    {
	Var *v;
	size_t i;

	Words words = Str_Words(varnames, FALSE);
	for (i = 0; i < words.len; i++) {
	    const char *varname = words.words[i];
	    v = VarFind(varname, VAR_GLOBAL, FALSE);
	    if (v == NULL) {
		VAR_DEBUG1("Not unexporting \"%s\" (not found)\n", varname);
		continue;
	    }

	    VAR_DEBUG1("Unexporting \"%s\"\n", varname);
	    if (!unexport_env && (v->flags & VAR_EXPORTED) &&
		!(v->flags & VAR_REEXPORT))
		unsetenv(v->name);
	    v->flags &= ~(unsigned)(VAR_EXPORTED | VAR_REEXPORT);

	    /*
	     * If we are unexporting a list,
	     * remove each one from .MAKE.EXPORTED.
	     * If we are removing them all,
	     * just delete .MAKE.EXPORTED below.
	     */
	    if (varnames == str) {
		/* XXX: v->name is injected without escaping it */
		char *expr = str_concat3("${" MAKE_EXPORTED ":N", v->name, "}");
		char *cp;
		(void)Var_Subst(expr, VAR_GLOBAL, VARE_WANTRES, &cp);
		/* TODO: handle errors */
		Var_Set(MAKE_EXPORTED, cp, VAR_GLOBAL);
		free(cp);
		free(expr);
	    }
	}
	Words_Free(words);
	if (varnames != str) {
	    Var_Delete(MAKE_EXPORTED, VAR_GLOBAL);
	    free(varnames_freeIt);
	}
    }
}

/* See Var_Set for documentation. */
void
Var_SetWithFlags(const char *name, const char *val, GNode *ctxt,
		 VarSetFlags flags)
{
    const char *unexpanded_name = name;
    char *name_freeIt = NULL;
    Var *v;

    assert(val != NULL);

    if (strchr(name, '$') != NULL) {
	(void)Var_Subst(name, ctxt, VARE_WANTRES, &name_freeIt);
	/* TODO: handle errors */
	name = name_freeIt;
    }

    if (name[0] == '\0') {
	VAR_DEBUG2("Var_Set(\"%s\", \"%s\", ...) "
		   "name expands to empty string - ignored\n",
		   unexpanded_name, val);
	free(name_freeIt);
	return;
    }

    if (ctxt == VAR_GLOBAL) {
	v = VarFind(name, VAR_CMDLINE, FALSE);
	if (v != NULL) {
	    if (v->flags & VAR_FROM_CMD) {
		VAR_DEBUG3("%s:%s = %s ignored!\n", ctxt->name, name, val);
		goto out;
	    }
	    VarFreeEnv(v, TRUE);
	}
    }

    /*
     * We only look for a variable in the given context since anything set
     * here will override anything in a lower context, so there's not much
     * point in searching them all just to save a bit of memory...
     */
    v = VarFind(name, ctxt, FALSE);
    if (v == NULL) {
	if (ctxt == VAR_CMDLINE && !(flags & VAR_SET_NO_EXPORT)) {
	    /*
	     * This var would normally prevent the same name being added
	     * to VAR_GLOBAL, so delete it from there if needed.
	     * Otherwise -V name may show the wrong value.
	     */
	    /* XXX: name is expanded for the second time */
	    Var_Delete(name, VAR_GLOBAL);
	}
	VarAdd(name, val, ctxt, flags);
    } else {
	if ((v->flags & VAR_READONLY) && !(flags & VAR_SET_READONLY)) {
	    VAR_DEBUG3("%s:%s = %s ignored (read-only)\n",
		       ctxt->name, name, val);
	    goto out;
	}
	Buf_Empty(&v->val);
	Buf_AddStr(&v->val, val);

	VAR_DEBUG3("%s:%s = %s\n", ctxt->name, name, val);
	if (v->flags & VAR_EXPORTED) {
	    Var_Export1(name, VAR_EXPORT_PARENT);
	}
    }
    /*
     * Any variables given on the command line are automatically exported
     * to the environment (as per POSIX standard)
     * Other than internals.
     */
    if (ctxt == VAR_CMDLINE && !(flags & VAR_SET_NO_EXPORT) && name[0] != '.') {
	if (v == NULL)
	    v = VarFind(name, ctxt, FALSE); /* we just added it */
	v->flags |= VAR_FROM_CMD;

	/*
	 * If requested, don't export these in the environment
	 * individually.  We still put them in MAKEOVERRIDES so
	 * that the command-line settings continue to override
	 * Makefile settings.
	 */
	if (!opts.varNoExportEnv)
	    setenv(name, val, 1);

	Var_Append(MAKEOVERRIDES, name, VAR_GLOBAL);
    }
    if (name[0] == '.' && strcmp(name, MAKE_SAVE_DOLLARS) == 0)
	save_dollars = ParseBoolean(val, save_dollars);

out:
    free(name_freeIt);
    if (v != NULL)
	VarFreeEnv(v, TRUE);
}

/*-
 *-----------------------------------------------------------------------
 * Var_Set --
 *	Set the variable name to the value val in the given context.
 *
 *	If the variable doesn't yet exist, it is created.
 *	Otherwise the new value overwrites and replaces the old value.
 *
 * Input:
 *	name		name of the variable to set, is expanded once
 *	val		value to give to the variable
 *	ctxt		context in which to set it
 *
 * Notes:
 *	The variable is searched for only in its context before being
 *	created in that context. I.e. if the context is VAR_GLOBAL,
 *	only VAR_GLOBAL->context is searched. Likewise if it is VAR_CMDLINE,
 *	only VAR_CMDLINE->context is searched. This is done to avoid the
 *	literally thousands of unnecessary strcmp's that used to be done to
 *	set, say, $(@) or $(<).
 *	If the context is VAR_GLOBAL though, we check if the variable
 *	was set in VAR_CMDLINE from the command line and skip it if so.
 *-----------------------------------------------------------------------
 */
void
Var_Set(const char *name, const char *val, GNode *ctxt)
{
    Var_SetWithFlags(name, val, ctxt, VAR_SET_NONE);
}

/*-
 *-----------------------------------------------------------------------
 * Var_Append --
 *	The variable of the given name has the given value appended to it in
 *	the given context.
 *
 *	If the variable doesn't exist, it is created. Otherwise the strings
 *	are concatenated, with a space in between.
 *
 * Input:
 *	name		name of the variable to modify, is expanded once
 *	val		string to append to it
 *	ctxt		context in which this should occur
 *
 * Notes:
 *	Only if the variable is being sought in the global context is the
 *	environment searched.
 *	XXX: Knows its calling circumstances in that if called with ctxt
 *	an actual target, it will only search that context since only
 *	a local variable could be being appended to. This is actually
 *	a big win and must be tolerated.
 *-----------------------------------------------------------------------
 */
void
Var_Append(const char *name, const char *val, GNode *ctxt)
{
    char *name_freeIt = NULL;
    Var *v;

    assert(val != NULL);

    if (strchr(name, '$') != NULL) {
	const char *unexpanded_name = name;
	(void)Var_Subst(name, ctxt, VARE_WANTRES, &name_freeIt);
	/* TODO: handle errors */
	name = name_freeIt;
	if (name[0] == '\0') {
	    VAR_DEBUG2("Var_Append(\"%s\", \"%s\", ...) "
		       "name expands to empty string - ignored\n",
		       unexpanded_name, val);
	    free(name_freeIt);
	    return;
	}
    }

    v = VarFind(name, ctxt, ctxt == VAR_GLOBAL);

    if (v == NULL) {
	/* XXX: name is expanded for the second time */
	Var_Set(name, val, ctxt);
    } else if (v->flags & VAR_READONLY) {
	VAR_DEBUG1("Ignoring append to %s since it is read-only\n", name);
    } else if (ctxt == VAR_CMDLINE || !(v->flags & VAR_FROM_CMD)) {
	Buf_AddByte(&v->val, ' ');
	Buf_AddStr(&v->val, val);

	VAR_DEBUG3("%s:%s = %s\n",
		   ctxt->name, name, Buf_GetAll(&v->val, NULL));

	if (v->flags & VAR_FROM_ENV) {
	    /*
	     * If the original variable came from the environment, we
	     * have to install it in the global context (we could place
	     * it in the environment, but then we should provide a way to
	     * export other variables...)
	     */
	    v->flags &= ~(unsigned)VAR_FROM_ENV;
	    /* This is the only place where a variable is created whose
	     * v->name is not the same as ctxt->context->key. */
	    HashTable_Set(&ctxt->context, name, v);
	}
    }
    free(name_freeIt);
}

/* See if the given variable exists, in the given context or in other
 * fallback contexts.
 *
 * Input:
 *	name		Variable to find, is expanded once
 *	ctxt		Context in which to start search
 */
Boolean
Var_Exists(const char *name, GNode *ctxt)
{
    char *name_freeIt = NULL;
    Var *v;

    if (strchr(name, '$') != NULL) {
	(void)Var_Subst(name, ctxt, VARE_WANTRES, &name_freeIt);
	/* TODO: handle errors */
	name = name_freeIt;
    }

    v = VarFind(name, ctxt, TRUE);
    free(name_freeIt);
    if (v == NULL)
	return FALSE;

    (void)VarFreeEnv(v, TRUE);
    return TRUE;
}

/*-
 *-----------------------------------------------------------------------
 * Var_Value --
 *	Return the unexpanded value of the given variable in the given
 *	context, or the usual contexts.
 *
 * Input:
 *	name		name to find, is not expanded any further
 *	ctxt		context in which to search for it
 *
 * Results:
 *	The value if the variable exists, NULL if it doesn't.
 *	If the returned value is not NULL, the caller must free
 *	out_freeIt when the returned value is no longer needed.
 *-----------------------------------------------------------------------
 */
const char *
Var_Value(const char *name, GNode *ctxt, void **out_freeIt)
{
    Var *v = VarFind(name, ctxt, TRUE);
    char *value;

    *out_freeIt = NULL;
    if (v == NULL)
	return NULL;

    value = Buf_GetAll(&v->val, NULL);
    if (VarFreeEnv(v, FALSE))
	*out_freeIt = value;
    return value;
}

/* Return the unexpanded variable value from this node, without trying to look
 * up the variable in any other context. */
const char *
Var_ValueDirect(const char *name, GNode *ctxt)
{
    Var *v = VarFind(name, ctxt, FALSE);
    return v != NULL ? Buf_GetAll(&v->val, NULL) : NULL;
}


/* SepBuf is a string being built from words, interleaved with separators. */
typedef struct SepBuf {
    Buffer buf;
    Boolean needSep;
    char sep;			/* usually ' ', but see the :ts modifier */
} SepBuf;

static void
SepBuf_Init(SepBuf *buf, char sep)
{
    Buf_InitSize(&buf->buf, 32);
    buf->needSep = FALSE;
    buf->sep = sep;
}

static void
SepBuf_Sep(SepBuf *buf)
{
    buf->needSep = TRUE;
}

static void
SepBuf_AddBytes(SepBuf *buf, const char *mem, size_t mem_size)
{
    if (mem_size == 0)
	return;
    if (buf->needSep && buf->sep != '\0') {
	Buf_AddByte(&buf->buf, buf->sep);
	buf->needSep = FALSE;
    }
    Buf_AddBytes(&buf->buf, mem, mem_size);
}

static void
SepBuf_AddBytesBetween(SepBuf *buf, const char *start, const char *end)
{
    SepBuf_AddBytes(buf, start, (size_t)(end - start));
}

static void
SepBuf_AddStr(SepBuf *buf, const char *str)
{
    SepBuf_AddBytes(buf, str, strlen(str));
}

static char *
SepBuf_Destroy(SepBuf *buf, Boolean free_buf)
{
    return Buf_Destroy(&buf->buf, free_buf);
}


/* This callback for ModifyWords gets a single word from a variable expression
 * and typically adds a modification of this word to the buffer. It may also
 * do nothing or add several words.
 *
 * For example, in ${:Ua b c:M*2}, the callback is called 3 times, once for
 * each word of "a b c". */
typedef void (*ModifyWordsCallback)(const char *word, SepBuf *buf, void *data);


/* Callback for ModifyWords to implement the :H modifier.
 * Add the dirname of the given word to the buffer. */
static void
ModifyWord_Head(const char *word, SepBuf *buf, void *dummy MAKE_ATTR_UNUSED)
{
    const char *slash = strrchr(word, '/');
    if (slash != NULL)
	SepBuf_AddBytesBetween(buf, word, slash);
    else
	SepBuf_AddStr(buf, ".");
}

/* Callback for ModifyWords to implement the :T modifier.
 * Add the basename of the given word to the buffer. */
static void
ModifyWord_Tail(const char *word, SepBuf *buf, void *dummy MAKE_ATTR_UNUSED)
{
    const char *slash = strrchr(word, '/');
    const char *base = slash != NULL ? slash + 1 : word;
    SepBuf_AddStr(buf, base);
}

/* Callback for ModifyWords to implement the :E modifier.
 * Add the filename suffix of the given word to the buffer, if it exists. */
static void
ModifyWord_Suffix(const char *word, SepBuf *buf, void *dummy MAKE_ATTR_UNUSED)
{
    const char *dot = strrchr(word, '.');
    if (dot != NULL)
	SepBuf_AddStr(buf, dot + 1);
}

/* Callback for ModifyWords to implement the :R modifier.
 * Add the basename of the given word to the buffer. */
static void
ModifyWord_Root(const char *word, SepBuf *buf, void *dummy MAKE_ATTR_UNUSED)
{
    const char *dot = strrchr(word, '.');
    size_t len = dot != NULL ? (size_t)(dot - word) : strlen(word);
    SepBuf_AddBytes(buf, word, len);
}

/* Callback for ModifyWords to implement the :M modifier.
 * Place the word in the buffer if it matches the given pattern. */
static void
ModifyWord_Match(const char *word, SepBuf *buf, void *data)
{
    const char *pattern = data;
    VAR_DEBUG2("VarMatch [%s] [%s]\n", word, pattern);
    if (Str_Match(word, pattern))
	SepBuf_AddStr(buf, word);
}

/* Callback for ModifyWords to implement the :N modifier.
 * Place the word in the buffer if it doesn't match the given pattern. */
static void
ModifyWord_NoMatch(const char *word, SepBuf *buf, void *data)
{
    const char *pattern = data;
    if (!Str_Match(word, pattern))
	SepBuf_AddStr(buf, word);
}

#ifdef SYSVVARSUB
/* Check word against pattern for a match (% is a wildcard).
 *
 * Input:
 *	word		Word to examine
 *	pattern		Pattern to examine against
 *
 * Results:
 *	Returns the start of the match, or NULL.
 *	out_match_len returns the length of the match, if any.
 *	out_hasPercent returns whether the pattern contains a percent.
 */
static const char *
SysVMatch(const char *word, const char *pattern,
	      size_t *out_match_len, Boolean *out_hasPercent)
{
    const char *p = pattern;
    const char *w = word;
    const char *percent;
    size_t w_len;
    size_t p_len;
    const char *w_tail;

    *out_hasPercent = FALSE;
    percent = strchr(p, '%');
    if (percent != NULL) {	/* ${VAR:...%...=...} */
	*out_hasPercent = TRUE;
	if (*w == '\0')
	    return NULL;	/* empty word does not match pattern */

	/* check that the prefix matches */
	for (; p != percent && *w != '\0' && *w == *p; w++, p++)
	    continue;
	if (p != percent)
	    return NULL;	/* No match */

	p++;			/* Skip the percent */
	if (*p == '\0') {
	    /* No more pattern, return the rest of the string */
	    *out_match_len = strlen(w);
	    return w;
	}
    }

    /* Test whether the tail matches */
    w_len = strlen(w);
    p_len = strlen(p);
    if (w_len < p_len)
	return NULL;

    w_tail = w + w_len - p_len;
    if (memcmp(p, w_tail, p_len) != 0)
	return NULL;

    *out_match_len = (size_t)(w_tail - w);
    return w;
}

struct ModifyWord_SYSVSubstArgs {
    GNode *ctx;
    const char *lhs;
    const char *rhs;
};

/* Callback for ModifyWords to implement the :%.from=%.to modifier. */
static void
ModifyWord_SYSVSubst(const char *word, SepBuf *buf, void *data)
{
    const struct ModifyWord_SYSVSubstArgs *args = data;
    char *rhs_expanded;
    const char *rhs;
    const char *percent;

    size_t match_len;
    Boolean lhsPercent;
    const char *match = SysVMatch(word, args->lhs, &match_len, &lhsPercent);
    if (match == NULL) {
	SepBuf_AddStr(buf, word);
	return;
    }

    /* Append rhs to the buffer, substituting the first '%' with the
     * match, but only if the lhs had a '%' as well. */

    (void)Var_Subst(args->rhs, args->ctx, VARE_WANTRES, &rhs_expanded);
    /* TODO: handle errors */

    rhs = rhs_expanded;
    percent = strchr(rhs, '%');

    if (percent != NULL && lhsPercent) {
	/* Copy the prefix of the replacement pattern */
	SepBuf_AddBytesBetween(buf, rhs, percent);
	rhs = percent + 1;
    }
    if (percent != NULL || !lhsPercent)
	SepBuf_AddBytes(buf, match, match_len);

    /* Append the suffix of the replacement pattern */
    SepBuf_AddStr(buf, rhs);

    free(rhs_expanded);
}
#endif


struct ModifyWord_SubstArgs {
    const char	*lhs;
    size_t	lhsLen;
    const char	*rhs;
    size_t	rhsLen;
    VarPatternFlags pflags;
    Boolean	matched;
};

/* Callback for ModifyWords to implement the :S,from,to, modifier.
 * Perform a string substitution on the given word. */
static void
ModifyWord_Subst(const char *word, SepBuf *buf, void *data)
{
    size_t wordLen = strlen(word);
    struct ModifyWord_SubstArgs *args = data;
    const char *match;

    if ((args->pflags & VARP_SUB_ONE) && args->matched)
	goto nosub;

    if (args->pflags & VARP_ANCHOR_START) {
	if (wordLen < args->lhsLen ||
	    memcmp(word, args->lhs, args->lhsLen) != 0)
	    goto nosub;

	if ((args->pflags & VARP_ANCHOR_END) && wordLen != args->lhsLen)
	    goto nosub;

	/* :S,^prefix,replacement, or :S,^whole$,replacement, */
	SepBuf_AddBytes(buf, args->rhs, args->rhsLen);
	SepBuf_AddBytes(buf, word + args->lhsLen, wordLen - args->lhsLen);
	args->matched = TRUE;
	return;
    }

    if (args->pflags & VARP_ANCHOR_END) {
	const char *start;

	if (wordLen < args->lhsLen)
	    goto nosub;

	start = word + (wordLen - args->lhsLen);
	if (memcmp(start, args->lhs, args->lhsLen) != 0)
	    goto nosub;

	/* :S,suffix$,replacement, */
	SepBuf_AddBytesBetween(buf, word, start);
	SepBuf_AddBytes(buf, args->rhs, args->rhsLen);
	args->matched = TRUE;
	return;
    }

    if (args->lhs[0] == '\0')
	goto nosub;

    /* unanchored case, may match more than once */
    while ((match = strstr(word, args->lhs)) != NULL) {
	SepBuf_AddBytesBetween(buf, word, match);
	SepBuf_AddBytes(buf, args->rhs, args->rhsLen);
	args->matched = TRUE;
	wordLen -= (size_t)(match - word) + args->lhsLen;
	word += (size_t)(match - word) + args->lhsLen;
	if (wordLen == 0 || !(args->pflags & VARP_SUB_GLOBAL))
	    break;
    }
nosub:
    SepBuf_AddBytes(buf, word, wordLen);
}

#ifndef NO_REGEX
/* Print the error caused by a regcomp or regexec call. */
static void
VarREError(int reerr, const regex_t *pat, const char *str)
{
    size_t errlen = regerror(reerr, pat, NULL, 0);
    char *errbuf = bmake_malloc(errlen);
    regerror(reerr, pat, errbuf, errlen);
    Error("%s: %s", str, errbuf);
    free(errbuf);
}

struct ModifyWord_SubstRegexArgs {
    regex_t re;
    size_t nsub;
    char *replace;
    VarPatternFlags pflags;
    Boolean matched;
};

/* Callback for ModifyWords to implement the :C/from/to/ modifier.
 * Perform a regex substitution on the given word. */
static void
ModifyWord_SubstRegex(const char *word, SepBuf *buf, void *data)
{
    struct ModifyWord_SubstRegexArgs *args = data;
    int xrv;
    const char *wp = word;
    char *rp;
    int flags = 0;
    regmatch_t m[10];

    if ((args->pflags & VARP_SUB_ONE) && args->matched)
	goto nosub;

tryagain:
    xrv = regexec(&args->re, wp, args->nsub, m, flags);

    switch (xrv) {
    case 0:
	args->matched = TRUE;
	SepBuf_AddBytes(buf, wp, (size_t)m[0].rm_so);

	for (rp = args->replace; *rp; rp++) {
	    if (*rp == '\\' && (rp[1] == '&' || rp[1] == '\\')) {
		SepBuf_AddBytes(buf, rp + 1, 1);
		rp++;
		continue;
	    }

	    if (*rp == '&') {
		SepBuf_AddBytesBetween(buf, wp + m[0].rm_so, wp + m[0].rm_eo);
		continue;
	    }

	    if (*rp != '\\' || !ch_isdigit(rp[1])) {
		SepBuf_AddBytes(buf, rp, 1);
		continue;
	    }

	    {			/* \0 to \9 backreference */
		size_t n = (size_t)(rp[1] - '0');
		rp++;

		if (n >= args->nsub) {
		    Error("No subexpression \\%zu", n);
		} else if (m[n].rm_so == -1) {
		    Error("No match for subexpression \\%zu", n);
		} else {
		    SepBuf_AddBytesBetween(buf, wp + m[n].rm_so,
					   wp + m[n].rm_eo);
		}
	    }
	}

	wp += m[0].rm_eo;
	if (args->pflags & VARP_SUB_GLOBAL) {
	    flags |= REG_NOTBOL;
	    if (m[0].rm_so == 0 && m[0].rm_eo == 0) {
		SepBuf_AddBytes(buf, wp, 1);
		wp++;
	    }
	    if (*wp)
		goto tryagain;
	}
	if (*wp) {
	    SepBuf_AddStr(buf, wp);
	}
	break;
    default:
	VarREError(xrv, &args->re, "Unexpected regex error");
	/* FALLTHROUGH */
    case REG_NOMATCH:
    nosub:
	SepBuf_AddStr(buf, wp);
	break;
    }
}
#endif


struct ModifyWord_LoopArgs {
    GNode	*ctx;
    char	*tvar;		/* name of temporary variable */
    char	*str;		/* string to expand */
    VarEvalFlags eflags;
};

/* Callback for ModifyWords to implement the :@var@...@ modifier of ODE make. */
static void
ModifyWord_Loop(const char *word, SepBuf *buf, void *data)
{
    const struct ModifyWord_LoopArgs *args;
    char *s;

    if (word[0] == '\0')
	return;

    args = data;
    Var_SetWithFlags(args->tvar, word, args->ctx, VAR_SET_NO_EXPORT);
    (void)Var_Subst(args->str, args->ctx, args->eflags, &s);
    /* TODO: handle errors */

    VAR_DEBUG4("ModifyWord_Loop: "
	       "in \"%s\", replace \"%s\" with \"%s\" to \"%s\"\n",
	       word, args->tvar, args->str, s);

    if (s[0] == '\n' || Buf_EndsWith(&buf->buf, '\n'))
	buf->needSep = FALSE;
    SepBuf_AddStr(buf, s);
    free(s);
}


/* The :[first..last] modifier selects words from the expression.
 * It can also reverse the words. */
static char *
VarSelectWords(char sep, Boolean oneBigWord, const char *str, int first,
	       int last)
{
    Words words;
    int len, start, end, step;
    int i;

    SepBuf buf;
    SepBuf_Init(&buf, sep);

    if (oneBigWord) {
	/* fake what Str_Words() would do if there were only one word */
	words.len = 1;
	words.words = bmake_malloc((words.len + 1) * sizeof(words.words[0]));
	words.freeIt = bmake_strdup(str);
	words.words[0] = words.freeIt;
	words.words[1] = NULL;
    } else {
	words = Str_Words(str, FALSE);
    }

    /*
     * Now sanitize the given range.
     * If first or last are negative, convert them to the positive equivalents
     * (-1 gets converted to ac, -2 gets converted to (ac - 1), etc.).
     */
    len = (int)words.len;
    if (first < 0)
	first += len + 1;
    if (last < 0)
	last += len + 1;

    /*
     * We avoid scanning more of the list than we need to.
     */
    if (first > last) {
	start = (first > len ? len : first) - 1;
	end = last < 1 ? 0 : last - 1;
	step = -1;
    } else {
	start = first < 1 ? 0 : first - 1;
	end = last > len ? len : last;
	step = 1;
    }

    for (i = start; (step < 0) == (i >= end); i += step) {
	SepBuf_AddStr(&buf, words.words[i]);
	SepBuf_Sep(&buf);
    }

    Words_Free(words);

    return SepBuf_Destroy(&buf, FALSE);
}


/* Callback for ModifyWords to implement the :tA modifier.
 * Replace each word with the result of realpath() if successful. */
static void
ModifyWord_Realpath(const char *word, SepBuf *buf, void *data MAKE_ATTR_UNUSED)
{
    struct stat st;
    char rbuf[MAXPATHLEN];

    const char *rp = cached_realpath(word, rbuf);
    if (rp != NULL && *rp == '/' && stat(rp, &st) == 0)
	word = rp;

    SepBuf_AddStr(buf, word);
}

/* Modify each of the words of the passed string using the given function.
 *
 * Input:
 *	str		String whose words should be modified
 *	modifyWord	Function that modifies a single word
 *	modifyWord_args Custom arguments for modifyWord
 *
 * Results:
 *	A string of all the words modified appropriately.
 *-----------------------------------------------------------------------
 */
static char *
ModifyWords(const char *str,
	    ModifyWordsCallback modifyWord, void *modifyWord_args,
	    Boolean oneBigWord, char sep)
{
    SepBuf result;
    Words words;
    size_t i;

    if (oneBigWord) {
	SepBuf_Init(&result, sep);
	modifyWord(str, &result, modifyWord_args);
	return SepBuf_Destroy(&result, FALSE);
    }

    SepBuf_Init(&result, sep);

    words = Str_Words(str, FALSE);

    VAR_DEBUG2("ModifyWords: split \"%s\" into %zu words\n", str, words.len);

    for (i = 0; i < words.len; i++) {
	modifyWord(words.words[i], &result, modifyWord_args);
	if (Buf_Len(&result.buf) > 0)
	    SepBuf_Sep(&result);
    }

    Words_Free(words);

    return SepBuf_Destroy(&result, FALSE);
}


static char *
Words_JoinFree(Words words)
{
    Buffer buf;
    size_t i;

    Buf_Init(&buf);

    for (i = 0; i < words.len; i++) {
	if (i != 0)
	    Buf_AddByte(&buf, ' ');	/* XXX: st->sep, for consistency */
	Buf_AddStr(&buf, words.words[i]);
    }

    Words_Free(words);

    return Buf_Destroy(&buf, FALSE);
}

/* Remove adjacent duplicate words. */
static char *
VarUniq(const char *str)
{
    Words words = Str_Words(str, FALSE);

    if (words.len > 1) {
	size_t i, j;
	for (j = 0, i = 1; i < words.len; i++)
	    if (strcmp(words.words[i], words.words[j]) != 0 && (++j != i))
		words.words[j] = words.words[i];
	words.len = j + 1;
    }

    return Words_JoinFree(words);
}


/* Quote shell meta-characters and space characters in the string.
 * If quoteDollar is set, also quote and double any '$' characters. */
static char *
VarQuote(const char *str, Boolean quoteDollar)
{
    Buffer buf;
    Buf_Init(&buf);

    for (; *str != '\0'; str++) {
	if (*str == '\n') {
	    const char *newline = Shell_GetNewline();
	    if (newline == NULL)
		newline = "\\\n";
	    Buf_AddStr(&buf, newline);
	    continue;
	}
	if (ch_isspace(*str) || is_shell_metachar((unsigned char)*str))
	    Buf_AddByte(&buf, '\\');
	Buf_AddByte(&buf, *str);
	if (quoteDollar && *str == '$')
	    Buf_AddStr(&buf, "\\$");
    }

    return Buf_Destroy(&buf, FALSE);
}

/* Compute the 32-bit hash of the given string, using the MurmurHash3
 * algorithm. Output is encoded as 8 hex digits, in Little Endian order. */
static char *
VarHash(const char *str)
{
    static const char    hexdigits[16] = "0123456789abcdef";
    const unsigned char *ustr = (const unsigned char *)str;

    uint32_t h  = 0x971e137bU;
    uint32_t c1 = 0x95543787U;
    uint32_t c2 = 0x2ad7eb25U;
    size_t len2 = strlen(str);

    char *buf;
    size_t i;

    size_t len;
    for (len = len2; len; ) {
	uint32_t k = 0;
	switch (len) {
	default:
	    k = ((uint32_t)ustr[3] << 24) |
		((uint32_t)ustr[2] << 16) |
		((uint32_t)ustr[1] << 8) |
		(uint32_t)ustr[0];
	    len -= 4;
	    ustr += 4;
	    break;
	case 3:
	    k |= (uint32_t)ustr[2] << 16;
	    /* FALLTHROUGH */
	case 2:
	    k |= (uint32_t)ustr[1] << 8;
	    /* FALLTHROUGH */
	case 1:
	    k |= (uint32_t)ustr[0];
	    len = 0;
	}
	c1 = c1 * 5 + 0x7b7d159cU;
	c2 = c2 * 5 + 0x6bce6396U;
	k *= c1;
	k = (k << 11) ^ (k >> 21);
	k *= c2;
	h = (h << 13) ^ (h >> 19);
	h = h * 5 + 0x52dce729U;
	h ^= k;
    }
    h ^= (uint32_t)len2;
    h *= 0x85ebca6b;
    h ^= h >> 13;
    h *= 0xc2b2ae35;
    h ^= h >> 16;

    buf = bmake_malloc(9);
    for (i = 0; i < 8; i++) {
	buf[i] = hexdigits[h & 0x0f];
	h >>= 4;
    }
    buf[8] = '\0';
    return buf;
}

static char *
VarStrftime(const char *fmt, Boolean zulu, time_t tim)
{
    char buf[BUFSIZ];

    if (tim == 0)
	time(&tim);
    if (*fmt == '\0')
	fmt = "%c";
    strftime(buf, sizeof buf, fmt, zulu ? gmtime(&tim) : localtime(&tim));

    buf[sizeof buf - 1] = '\0';
    return bmake_strdup(buf);
}

/*
 * The ApplyModifier functions take an expression that is being evaluated.
 * Their task is to apply a single modifier to the expression.
 * To do this, they parse the modifier and its parameters from pp and apply
 * the parsed modifier to the current value of the expression, generating a
 * new value from it.
 *
 * The modifier typically lasts until the next ':', or a closing '}' or ')'
 * (taken from st->endc), or the end of the string (parse error).
 *
 * The high-level behavior of these functions is:
 *
 * 1. parse the modifier
 * 2. evaluate the modifier
 * 3. housekeeping
 *
 * Parsing the modifier
 *
 * If parsing succeeds, the parsing position *pp is updated to point to the
 * first character following the modifier, which typically is either ':' or
 * st->endc.  The modifier doesn't have to check for this delimiter character,
 * this is done by ApplyModifiers.
 *
 * XXX: As of 2020-11-15, some modifiers such as :S, :C, :P, :L do not
 * need to be followed by a ':' or endc; this was an unintended mistake.
 *
 * If parsing fails because of a missing delimiter (as in the :S, :C or :@
 * modifiers), return AMR_CLEANUP.
 *
 * If parsing fails because the modifier is unknown, return AMR_UNKNOWN to
 * try the SysV modifier ${VAR:from=to} as fallback.  This should only be
 * done as long as there have been no side effects from evaluating nested
 * variables, to avoid evaluating them more than once.  In this case, the
 * parsing position may or may not be updated.  (XXX: Why not? The original
 * parsing position is well-known in ApplyModifiers.)
 *
 * If parsing fails and the SysV modifier ${VAR:from=to} should not be used
 * as a fallback, either issue an error message using Error or Parse_Error
 * and then return AMR_CLEANUP, or return AMR_BAD for the default error
 * message.  Both of these return values will stop processing the variable
 * expression.  (XXX: As of 2020-08-23, evaluation of the whole string
 * continues nevertheless after skipping a few bytes, which essentially is
 * undefined behavior.  Not in the sense of C, but still it's impossible to
 * predict what happens in the parser.)
 *
 * Evaluating the modifier
 *
 * After parsing, the modifier is evaluated.  The side effects from evaluating
 * nested variable expressions in the modifier text often already happen
 * during parsing though.
 *
 * Evaluating the modifier usually takes the current value of the variable
 * expression from st->val, or the variable name from st->var->name and stores
 * the result in st->newVal.
 *
 * If evaluating fails (as of 2020-08-23), an error message is printed using
 * Error.  This function has no side-effects, it really just prints the error
 * message.  Processing the expression continues as if everything were ok.
 * XXX: This should be fixed by adding proper error handling to Var_Subst,
 * Var_Parse, ApplyModifiers and ModifyWords.
 *
 * Housekeeping
 *
 * Some modifiers such as :D and :U turn undefined expressions into defined
 * expressions (see VEF_UNDEF, VEF_DEF).
 *
 * Some modifiers need to free some memory.
 */

typedef enum VarExprFlags {
    /* The variable expression is based on an undefined variable. */
    VEF_UNDEF = 0x01,
    /* The variable expression started as an undefined expression, but one
     * of the modifiers (such as :D or :U) has turned the expression from
     * undefined to defined. */
    VEF_DEF = 0x02
} VarExprFlags;

ENUM_FLAGS_RTTI_2(VarExprFlags,
		  VEF_UNDEF, VEF_DEF);


typedef struct ApplyModifiersState {
    const char startc;		/* '\0' or '{' or '(' */
    const char endc;		/* '\0' or '}' or ')' */
    Var * const var;
    GNode * const ctxt;
    const VarEvalFlags eflags;

    char *val;			/* The old value of the expression,
				 * before applying the modifier, never NULL */
    char *newVal;		/* The new value of the expression,
				 * after applying the modifier, never NULL */
    char sep;			/* Word separator in expansions
				 * (see the :ts modifier) */
    Boolean oneBigWord;		/* TRUE if some modifiers that otherwise split
				 * the variable value into words, like :S and
				 * :C, treat the variable value as a single big
				 * word, possibly containing spaces. */
    VarExprFlags exprFlags;
} ApplyModifiersState;

static void
ApplyModifiersState_Define(ApplyModifiersState *st)
{
    if (st->exprFlags & VEF_UNDEF)
	st->exprFlags |= VEF_DEF;
}

typedef enum ApplyModifierResult {
    AMR_OK,			/* Continue parsing */
    AMR_UNKNOWN,		/* Not a match, try other modifiers as well */
    AMR_BAD,			/* Error out with "Bad modifier" message */
    AMR_CLEANUP			/* Error out without error message */
} ApplyModifierResult;

/* Allow backslashes to escape the delimiter, $, and \, but don't touch other
 * backslashes. */
static Boolean
IsEscapedModifierPart(const char *p, char delim,
		      struct ModifyWord_SubstArgs *subst)
{
    if (p[0] != '\\')
	return FALSE;
    if (p[1] == delim || p[1] == '\\' || p[1] == '$')
	return TRUE;
    return p[1] == '&' && subst != NULL;
}

/*
 * Parse a part of a modifier such as the "from" and "to" in :S/from/to/ or
 * the "var" or "replacement ${var}" in :@var@replacement ${var}@, up to and
 * including the next unescaped delimiter.  The delimiter, as well as the
 * backslash or the dollar, can be escaped with a backslash.
 *
 * Return the parsed (and possibly expanded) string, or NULL if no delimiter
 * was found.  On successful return, the parsing position pp points right
 * after the delimiter.  The delimiter is not included in the returned
 * value though.
 */
static VarParseResult
ParseModifierPart(
    const char **pp,		/* The parsing position, updated upon return */
    char delim,			/* Parsing stops at this delimiter */
    VarEvalFlags eflags,	/* Flags for evaluating nested variables;
				 * if VARE_WANTRES is not set, the text is
				 * only parsed */
    ApplyModifiersState *st,
    char **out_part,
    size_t *out_length,		/* Optionally stores the length of the returned
				 * string, just to save another strlen call. */
    VarPatternFlags *out_pflags,/* For the first part of the :S modifier,
				 * sets the VARP_ANCHOR_END flag if the last
				 * character of the pattern is a $. */
    struct ModifyWord_SubstArgs *subst
				/* For the second part of the :S modifier,
				 * allow ampersands to be escaped and replace
				 * unescaped ampersands with subst->lhs. */
) {
    Buffer buf;
    const char *p;

    Buf_Init(&buf);

    /*
     * Skim through until the matching delimiter is found; pick up variable
     * expressions on the way.
     */
    p = *pp;
    while (*p != '\0' && *p != delim) {
	const char *varstart;

	if (IsEscapedModifierPart(p, delim, subst)) {
	    Buf_AddByte(&buf, p[1]);
	    p += 2;
	    continue;
	}

	if (*p != '$') {	/* Unescaped, simple text */
	    if (subst != NULL && *p == '&')
		Buf_AddBytes(&buf, subst->lhs, subst->lhsLen);
	    else
		Buf_AddByte(&buf, *p);
	    p++;
	    continue;
	}

	if (p[1] == delim) {	/* Unescaped $ at end of pattern */
	    if (out_pflags != NULL)
		*out_pflags |= VARP_ANCHOR_END;
	    else
		Buf_AddByte(&buf, *p);
	    p++;
	    continue;
	}

	if (eflags & VARE_WANTRES) {	/* Nested variable, evaluated */
	    const char *nested_p = p;
	    const char *nested_val;
	    void *nested_val_freeIt;
	    VarEvalFlags nested_eflags = eflags & ~(unsigned)VARE_KEEP_DOLLAR;

	    (void)Var_Parse(&nested_p, st->ctxt, nested_eflags,
			    &nested_val, &nested_val_freeIt);
	    /* TODO: handle errors */
	    Buf_AddStr(&buf, nested_val);
	    free(nested_val_freeIt);
	    p += nested_p - p;
	    continue;
	}

	/* XXX: This whole block is very similar to Var_Parse without
	 * VARE_WANTRES.  There may be subtle edge cases though that are
	 * not yet covered in the unit tests and that are parsed differently,
	 * depending on whether they are evaluated or not.
	 *
	 * This subtle difference is not documented in the manual page,
	 * neither is the difference between parsing :D and :M documented.
	 * No code should ever depend on these details, but who knows. */

	varstart = p;		/* Nested variable, only parsed */
	if (p[1] == '(' || p[1] == '{') {
	    /*
	     * Find the end of this variable reference
	     * and suck it in without further ado.
	     * It will be interpreted later.
	     */
	    char startc = p[1];
	    int endc = startc == '(' ? ')' : '}';
	    int depth = 1;

	    for (p += 2; *p != '\0' && depth > 0; p++) {
		if (p[-1] != '\\') {
		    if (*p == startc)
			depth++;
		    if (*p == endc)
			depth--;
		}
	    }
	    Buf_AddBytesBetween(&buf, varstart, p);
	} else {
	    Buf_AddByte(&buf, *varstart);
	    p++;
	}
    }

    if (*p != delim) {
	*pp = p;
	Error("Unfinished modifier for %s ('%c' missing)",
	      st->var->name, delim);
	*out_part = NULL;
	return VPR_PARSE_MSG;
    }

    *pp = ++p;
    if (out_length != NULL)
	*out_length = Buf_Len(&buf);

    *out_part = Buf_Destroy(&buf, FALSE);
    VAR_DEBUG1("Modifier part: \"%s\"\n", *out_part);
    return VPR_OK;
}

/* Test whether mod starts with modname, followed by a delimiter. */
MAKE_INLINE Boolean
ModMatch(const char *mod, const char *modname, char endc)
{
    size_t n = strlen(modname);
    return strncmp(mod, modname, n) == 0 &&
	   (mod[n] == endc || mod[n] == ':');
}

/* Test whether mod starts with modname, followed by a delimiter or '='. */
MAKE_INLINE Boolean
ModMatchEq(const char *mod, const char *modname, char endc)
{
    size_t n = strlen(modname);
    return strncmp(mod, modname, n) == 0 &&
	   (mod[n] == endc || mod[n] == ':' || mod[n] == '=');
}

static Boolean
TryParseIntBase0(const char **pp, int *out_num)
{
    char *end;
    long n;

    errno = 0;
    n = strtol(*pp, &end, 0);
    if ((n == LONG_MIN || n == LONG_MAX) && errno == ERANGE)
	return FALSE;
    if (n < INT_MIN || n > INT_MAX)
	return FALSE;

    *pp = end;
    *out_num = (int)n;
    return TRUE;
}

static Boolean
TryParseSize(const char **pp, size_t *out_num)
{
    char *end;
    unsigned long n;

    if (!ch_isdigit(**pp))
	return FALSE;

    errno = 0;
    n = strtoul(*pp, &end, 10);
    if (n == ULONG_MAX && errno == ERANGE)
	return FALSE;
    if (n > SIZE_MAX)
	return FALSE;

    *pp = end;
    *out_num = (size_t)n;
    return TRUE;
}

static Boolean
TryParseChar(const char **pp, int base, char *out_ch)
{
    char *end;
    unsigned long n;

    if (!ch_isalnum(**pp))
	return FALSE;

    errno = 0;
    n = strtoul(*pp, &end, base);
    if (n == ULONG_MAX && errno == ERANGE)
	return FALSE;
    if (n > UCHAR_MAX)
	return FALSE;

    *pp = end;
    *out_ch = (char)n;
    return TRUE;
}

/* :@var@...${var}...@ */
static ApplyModifierResult
ApplyModifier_Loop(const char **pp, ApplyModifiersState *st)
{
    struct ModifyWord_LoopArgs args;
    char prev_sep;
    VarParseResult res;

    args.ctx = st->ctxt;

    (*pp)++;			/* Skip the first '@' */
    res = ParseModifierPart(pp, '@', VARE_NONE, st,
			    &args.tvar, NULL, NULL, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;
    if (opts.lint && strchr(args.tvar, '$') != NULL) {
	Parse_Error(PARSE_FATAL,
		    "In the :@ modifier of \"%s\", the variable name \"%s\" "
		    "must not contain a dollar.",
		    st->var->name, args.tvar);
	return AMR_CLEANUP;
    }

    res = ParseModifierPart(pp, '@', VARE_NONE, st,
			    &args.str, NULL, NULL, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;

    args.eflags = st->eflags & ~(unsigned)VARE_KEEP_DOLLAR;
    prev_sep = st->sep;
    st->sep = ' ';		/* XXX: should be st->sep for consistency */
    st->newVal = ModifyWords(st->val, ModifyWord_Loop, &args,
			     st->oneBigWord, st->sep);
    st->sep = prev_sep;
    /* XXX: Consider restoring the previous variable instead of deleting. */
    Var_Delete(args.tvar, st->ctxt);
    free(args.tvar);
    free(args.str);
    return AMR_OK;
}

/* :Ddefined or :Uundefined */
static ApplyModifierResult
ApplyModifier_Defined(const char **pp, ApplyModifiersState *st)
{
    Buffer buf;
    const char *p;

    VarEvalFlags eflags = VARE_NONE;
    if (st->eflags & VARE_WANTRES)
	if ((**pp == 'D') == !(st->exprFlags & VEF_UNDEF))
	    eflags = st->eflags;

    Buf_Init(&buf);
    p = *pp + 1;
    while (*p != st->endc && *p != ':' && *p != '\0') {

	/* XXX: This code is similar to the one in Var_Parse.
	 * See if the code can be merged.
	 * See also ApplyModifier_Match. */

	/* Escaped delimiter or other special character */
	if (*p == '\\') {
	    char c = p[1];
	    if (c == st->endc || c == ':' || c == '$' || c == '\\') {
		Buf_AddByte(&buf, c);
		p += 2;
		continue;
	    }
	}

	/* Nested variable expression */
	if (*p == '$') {
	    const char *nested_val;
	    void *nested_val_freeIt;

	    (void)Var_Parse(&p, st->ctxt, eflags,
			    &nested_val, &nested_val_freeIt);
	    /* TODO: handle errors */
	    Buf_AddStr(&buf, nested_val);
	    free(nested_val_freeIt);
	    continue;
	}

	/* Ordinary text */
	Buf_AddByte(&buf, *p);
	p++;
    }
    *pp = p;

    ApplyModifiersState_Define(st);

    if (eflags & VARE_WANTRES) {
	st->newVal = Buf_Destroy(&buf, FALSE);
    } else {
	st->newVal = st->val;
	Buf_Destroy(&buf, TRUE);
    }
    return AMR_OK;
}

/* :L */
static ApplyModifierResult
ApplyModifier_Literal(const char **pp, ApplyModifiersState *st)
{
    ApplyModifiersState_Define(st);
    st->newVal = bmake_strdup(st->var->name);
    (*pp)++;
    return AMR_OK;
}

static Boolean
TryParseTime(const char **pp, time_t *out_time)
{
    char *end;
    unsigned long n;

    if (!ch_isdigit(**pp))
	return FALSE;

    errno = 0;
    n = strtoul(*pp, &end, 10);
    if (n == ULONG_MAX && errno == ERANGE)
	return FALSE;

    *pp = end;
    *out_time = (time_t)n;	/* ignore possible truncation for now */
    return TRUE;
}

/* :gmtime */
static ApplyModifierResult
ApplyModifier_Gmtime(const char **pp, ApplyModifiersState *st)
{
    time_t utc;

    const char *mod = *pp;
    if (!ModMatchEq(mod, "gmtime", st->endc))
	return AMR_UNKNOWN;

    if (mod[6] == '=') {
	const char *arg = mod + 7;
	if (!TryParseTime(&arg, &utc)) {
	    Parse_Error(PARSE_FATAL, "Invalid time value: %s\n", mod + 7);
	    return AMR_CLEANUP;
	}
	*pp = arg;
    } else {
	utc = 0;
	*pp = mod + 6;
    }
    st->newVal = VarStrftime(st->val, TRUE, utc);
    return AMR_OK;
}

/* :localtime */
static ApplyModifierResult
ApplyModifier_Localtime(const char **pp, ApplyModifiersState *st)
{
    time_t utc;

    const char *mod = *pp;
    if (!ModMatchEq(mod, "localtime", st->endc))
	return AMR_UNKNOWN;

    if (mod[9] == '=') {
	const char *arg = mod + 10;
	if (!TryParseTime(&arg, &utc)) {
	    Parse_Error(PARSE_FATAL, "Invalid time value: %s\n", mod + 10);
	    return AMR_CLEANUP;
	}
	*pp = arg;
    } else {
	utc = 0;
	*pp = mod + 9;
    }
    st->newVal = VarStrftime(st->val, FALSE, utc);
    return AMR_OK;
}

/* :hash */
static ApplyModifierResult
ApplyModifier_Hash(const char **pp, ApplyModifiersState *st)
{
    if (!ModMatch(*pp, "hash", st->endc))
	return AMR_UNKNOWN;

    st->newVal = VarHash(st->val);
    *pp += 4;
    return AMR_OK;
}

/* :P */
static ApplyModifierResult
ApplyModifier_Path(const char **pp, ApplyModifiersState *st)
{
    GNode *gn;
    char *path;

    ApplyModifiersState_Define(st);

    gn = Targ_FindNode(st->var->name);
    if (gn == NULL || gn->type & OP_NOPATH) {
	path = NULL;
    } else if (gn->path != NULL) {
	path = bmake_strdup(gn->path);
    } else {
	SearchPath *searchPath = Suff_FindPath(gn);
	path = Dir_FindFile(st->var->name, searchPath);
    }
    if (path == NULL)
	path = bmake_strdup(st->var->name);
    st->newVal = path;

    (*pp)++;
    return AMR_OK;
}

/* :!cmd! */
static ApplyModifierResult
ApplyModifier_ShellCommand(const char **pp, ApplyModifiersState *st)
{
    char *cmd;
    const char *errfmt;
    VarParseResult res;

    (*pp)++;
    res = ParseModifierPart(pp, '!', st->eflags, st,
			    &cmd, NULL, NULL, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;

    errfmt = NULL;
    if (st->eflags & VARE_WANTRES)
	st->newVal = Cmd_Exec(cmd, &errfmt);
    else
	st->newVal = bmake_strdup("");
    free(cmd);

    if (errfmt != NULL)
	Error(errfmt, st->val);	/* XXX: why still return AMR_OK? */

    ApplyModifiersState_Define(st);
    return AMR_OK;
}

/* The :range modifier generates an integer sequence as long as the words.
 * The :range=7 modifier generates an integer sequence from 1 to 7. */
static ApplyModifierResult
ApplyModifier_Range(const char **pp, ApplyModifiersState *st)
{
    size_t n;
    Buffer buf;
    size_t i;

    const char *mod = *pp;
    if (!ModMatchEq(mod, "range", st->endc))
	return AMR_UNKNOWN;

    if (mod[5] == '=') {
	const char *p = mod + 6;
	if (!TryParseSize(&p, &n)) {
	    Parse_Error(PARSE_FATAL, "Invalid number: %s\n", mod + 6);
	    return AMR_CLEANUP;
	}
	*pp = p;
    } else {
	n = 0;
	*pp = mod + 5;
    }

    if (n == 0) {
	Words words = Str_Words(st->val, FALSE);
	n = words.len;
	Words_Free(words);
    }

    Buf_Init(&buf);

    for (i = 0; i < n; i++) {
	if (i != 0)
	    Buf_AddByte(&buf, ' ');	/* XXX: st->sep, for consistency */
	Buf_AddInt(&buf, 1 + (int)i);
    }

    st->newVal = Buf_Destroy(&buf, FALSE);
    return AMR_OK;
}

/* :Mpattern or :Npattern */
static ApplyModifierResult
ApplyModifier_Match(const char **pp, ApplyModifiersState *st)
{
    const char *mod = *pp;
    Boolean copy = FALSE;	/* pattern should be, or has been, copied */
    Boolean needSubst = FALSE;
    const char *endpat;
    char *pattern;
    ModifyWordsCallback callback;

    /*
     * In the loop below, ignore ':' unless we are at (or back to) the
     * original brace level.
     * XXX: This will likely not work right if $() and ${} are intermixed.
     */
    /* XXX: This code is similar to the one in Var_Parse.
     * See if the code can be merged.
     * See also ApplyModifier_Defined. */
    int nest = 0;
    const char *p;
    for (p = mod + 1; *p != '\0' && !(*p == ':' && nest == 0); p++) {
	if (*p == '\\' &&
	    (p[1] == ':' || p[1] == st->endc || p[1] == st->startc)) {
	    if (!needSubst)
		copy = TRUE;
	    p++;
	    continue;
	}
	if (*p == '$')
	    needSubst = TRUE;
	if (*p == '(' || *p == '{')
	    nest++;
	if (*p == ')' || *p == '}') {
	    nest--;
	    if (nest < 0)
		break;
	}
    }
    *pp = p;
    endpat = p;

    if (copy) {
	char *dst;
	const char *src;

	/* Compress the \:'s out of the pattern. */
	pattern = bmake_malloc((size_t)(endpat - (mod + 1)) + 1);
	dst = pattern;
	src = mod + 1;
	for (; src < endpat; src++, dst++) {
	    if (src[0] == '\\' && src + 1 < endpat &&
		/* XXX: st->startc is missing here; see above */
		(src[1] == ':' || src[1] == st->endc))
		src++;
	    *dst = *src;
	}
	*dst = '\0';
	endpat = dst;
    } else {
	pattern = bmake_strsedup(mod + 1, endpat);
    }

    if (needSubst) {
	/* pattern contains embedded '$', so use Var_Subst to expand it. */
	char *old_pattern = pattern;
	(void)Var_Subst(pattern, st->ctxt, st->eflags, &pattern);
	/* TODO: handle errors */
	free(old_pattern);
    }

    VAR_DEBUG3("Pattern[%s] for [%s] is [%s]\n",
	       st->var->name, st->val, pattern);

    callback = mod[0] == 'M' ? ModifyWord_Match : ModifyWord_NoMatch;
    st->newVal = ModifyWords(st->val, callback, pattern,
			     st->oneBigWord, st->sep);
    free(pattern);
    return AMR_OK;
}

/* :S,from,to, */
static ApplyModifierResult
ApplyModifier_Subst(const char **pp, ApplyModifiersState *st)
{
    struct ModifyWord_SubstArgs args;
    char *lhs, *rhs;
    Boolean oneBigWord;
    VarParseResult res;

    char delim = (*pp)[1];
    if (delim == '\0') {
	Error("Missing delimiter for :S modifier");
	(*pp)++;
	return AMR_CLEANUP;
    }

    *pp += 2;

    args.pflags = 0;
    args.matched = FALSE;

    /*
     * If pattern begins with '^', it is anchored to the
     * start of the word -- skip over it and flag pattern.
     */
    if (**pp == '^') {
	args.pflags |= VARP_ANCHOR_START;
	(*pp)++;
    }

    res = ParseModifierPart(pp, delim, st->eflags, st,
			    &lhs, &args.lhsLen, &args.pflags, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;
    args.lhs = lhs;

    res = ParseModifierPart(pp, delim, st->eflags, st,
			    &rhs, &args.rhsLen, NULL, &args);
    if (res != VPR_OK)
	return AMR_CLEANUP;
    args.rhs = rhs;

    oneBigWord = st->oneBigWord;
    for (;; (*pp)++) {
	switch (**pp) {
	case 'g':
	    args.pflags |= VARP_SUB_GLOBAL;
	    continue;
	case '1':
	    args.pflags |= VARP_SUB_ONE;
	    continue;
	case 'W':
	    oneBigWord = TRUE;
	    continue;
	}
	break;
    }

    st->newVal = ModifyWords(st->val, ModifyWord_Subst, &args,
			     oneBigWord, st->sep);

    free(lhs);
    free(rhs);
    return AMR_OK;
}

#ifndef NO_REGEX

/* :C,from,to, */
static ApplyModifierResult
ApplyModifier_Regex(const char **pp, ApplyModifiersState *st)
{
    char *re;
    struct ModifyWord_SubstRegexArgs args;
    Boolean oneBigWord;
    int error;
    VarParseResult res;

    char delim = (*pp)[1];
    if (delim == '\0') {
	Error("Missing delimiter for :C modifier");
	(*pp)++;
	return AMR_CLEANUP;
    }

    *pp += 2;

    res = ParseModifierPart(pp, delim, st->eflags, st,
			    &re, NULL, NULL, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;

    res = ParseModifierPart(pp, delim, st->eflags, st,
			    &args.replace, NULL, NULL, NULL);
    if (args.replace == NULL) {
	free(re);
	return AMR_CLEANUP;
    }

    args.pflags = 0;
    args.matched = FALSE;
    oneBigWord = st->oneBigWord;
    for (;; (*pp)++) {
	switch (**pp) {
	case 'g':
	    args.pflags |= VARP_SUB_GLOBAL;
	    continue;
	case '1':
	    args.pflags |= VARP_SUB_ONE;
	    continue;
	case 'W':
	    oneBigWord = TRUE;
	    continue;
	}
	break;
    }

    error = regcomp(&args.re, re, REG_EXTENDED);
    free(re);
    if (error) {
	VarREError(error, &args.re, "Regex compilation error");
	free(args.replace);
	return AMR_CLEANUP;
    }

    args.nsub = args.re.re_nsub + 1;
    if (args.nsub > 10)
	args.nsub = 10;
    st->newVal = ModifyWords(st->val, ModifyWord_SubstRegex, &args,
			     oneBigWord, st->sep);
    regfree(&args.re);
    free(args.replace);
    return AMR_OK;
}
#endif

/* :Q, :q */
static ApplyModifierResult
ApplyModifier_Quote(const char **pp, ApplyModifiersState *st)
{
    if ((*pp)[1] == st->endc || (*pp)[1] == ':') {
	st->newVal = VarQuote(st->val, **pp == 'q');
	(*pp)++;
	return AMR_OK;
    } else
	return AMR_UNKNOWN;
}

static void
ModifyWord_Copy(const char *word, SepBuf *buf, void *data MAKE_ATTR_UNUSED)
{
    SepBuf_AddStr(buf, word);
}

/* :ts<separator> */
static ApplyModifierResult
ApplyModifier_ToSep(const char **pp, ApplyModifiersState *st)
{
    const char *sep = *pp + 2;

    /* ":ts<any><endc>" or ":ts<any>:" */
    if (sep[0] != st->endc && (sep[1] == st->endc || sep[1] == ':')) {
	st->sep = sep[0];
	*pp = sep + 1;
	goto ok;
    }

    /* ":ts<endc>" or ":ts:" */
    if (sep[0] == st->endc || sep[0] == ':') {
	st->sep = '\0';		/* no separator */
	*pp = sep;
	goto ok;
    }

    /* ":ts<unrecognised><unrecognised>". */
    if (sep[0] != '\\') {
	(*pp)++;		/* just for backwards compatibility */
	return AMR_BAD;
    }

    /* ":ts\n" */
    if (sep[1] == 'n') {
	st->sep = '\n';
	*pp = sep + 2;
	goto ok;
    }

    /* ":ts\t" */
    if (sep[1] == 't') {
	st->sep = '\t';
	*pp = sep + 2;
	goto ok;
    }

    /* ":ts\x40" or ":ts\100" */
    {
	const char *p = sep + 1;
	int base = 8;		/* assume octal */

	if (sep[1] == 'x') {
	    base = 16;
	    p++;
	} else if (!ch_isdigit(sep[1])) {
	    (*pp)++;		/* just for backwards compatibility */
	    return AMR_BAD;	/* ":ts<backslash><unrecognised>". */
	}

	if (!TryParseChar(&p, base, &st->sep)) {
	    Parse_Error(PARSE_FATAL, "Invalid character number: %s\n", p);
	    return AMR_CLEANUP;
	}
	if (*p != ':' && *p != st->endc) {
	    (*pp)++;		/* just for backwards compatibility */
	    return AMR_BAD;
	}

	*pp = p;
    }

ok:
    st->newVal = ModifyWords(st->val, ModifyWord_Copy, NULL,
			     st->oneBigWord, st->sep);
    return AMR_OK;
}

/* :tA, :tu, :tl, :ts<separator>, etc. */
static ApplyModifierResult
ApplyModifier_To(const char **pp, ApplyModifiersState *st)
{
    const char *mod = *pp;
    assert(mod[0] == 't');

    if (mod[1] == st->endc || mod[1] == ':' || mod[1] == '\0') {
	*pp = mod + 1;
	return AMR_BAD;		/* Found ":t<endc>" or ":t:". */
    }

    if (mod[1] == 's')
	return ApplyModifier_ToSep(pp, st);

    if (mod[2] != st->endc && mod[2] != ':') {
	*pp = mod + 1;
	return AMR_BAD;		/* Found ":t<unrecognised><unrecognised>". */
    }

    /* Check for two-character options: ":tu", ":tl" */
    if (mod[1] == 'A') {	/* absolute path */
	st->newVal = ModifyWords(st->val, ModifyWord_Realpath, NULL,
				 st->oneBigWord, st->sep);
	*pp = mod + 2;
	return AMR_OK;
    }

    if (mod[1] == 'u') {	/* :tu */
	size_t i;
	size_t len = strlen(st->val);
	st->newVal = bmake_malloc(len + 1);
	for (i = 0; i < len + 1; i++)
	    st->newVal[i] = ch_toupper(st->val[i]);
	*pp = mod + 2;
	return AMR_OK;
    }

    if (mod[1] == 'l') {	/* :tl */
	size_t i;
	size_t len = strlen(st->val);
	st->newVal = bmake_malloc(len + 1);
	for (i = 0; i < len + 1; i++)
	    st->newVal[i] = ch_tolower(st->val[i]);
	*pp = mod + 2;
	return AMR_OK;
    }

    if (mod[1] == 'W' || mod[1] == 'w') { /* :tW, :tw */
	st->oneBigWord = mod[1] == 'W';
	st->newVal = st->val;
	*pp = mod + 2;
	return AMR_OK;
    }

    /* Found ":t<unrecognised>:" or ":t<unrecognised><endc>". */
    *pp = mod + 1;
    return AMR_BAD;
}

/* :[#], :[1], :[-1..1], etc. */
static ApplyModifierResult
ApplyModifier_Words(const char **pp, ApplyModifiersState *st)
{
    char *estr;
    int first, last;
    VarParseResult res;
    const char *p;

    (*pp)++;			/* skip the '[' */
    res = ParseModifierPart(pp, ']', st->eflags, st,
			    &estr, NULL, NULL, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;

    /* now *pp points just after the closing ']' */
    if (**pp != ':' && **pp != st->endc)
	goto bad_modifier;	/* Found junk after ']' */

    if (estr[0] == '\0')
	goto bad_modifier;	/* empty square brackets in ":[]". */

    if (estr[0] == '#' && estr[1] == '\0') { /* Found ":[#]" */
	if (st->oneBigWord) {
	    st->newVal = bmake_strdup("1");
	} else {
	    Buffer buf;

	    Words words = Str_Words(st->val, FALSE);
	    size_t ac = words.len;
	    Words_Free(words);

	    Buf_InitSize(&buf, 4);	/* 3 digits + '\0' is usually enough */
	    Buf_AddInt(&buf, (int)ac);
	    st->newVal = Buf_Destroy(&buf, FALSE);
	}
	goto ok;
    }

    if (estr[0] == '*' && estr[1] == '\0') {
	/* Found ":[*]" */
	st->oneBigWord = TRUE;
	st->newVal = st->val;
	goto ok;
    }

    if (estr[0] == '@' && estr[1] == '\0') {
	/* Found ":[@]" */
	st->oneBigWord = FALSE;
	st->newVal = st->val;
	goto ok;
    }

    /*
     * We expect estr to contain a single integer for :[N], or two integers
     * separated by ".." for :[start..end].
     */
    p = estr;
    if (!TryParseIntBase0(&p, &first))
	goto bad_modifier;	/* Found junk instead of a number */

    if (p[0] == '\0') {	/* Found only one integer in :[N] */
	last = first;
    } else if (p[0] == '.' && p[1] == '.' && p[2] != '\0') {
	/* Expecting another integer after ".." */
	p += 2;
	if (!TryParseIntBase0(&p, &last) || *p != '\0')
	    goto bad_modifier;	/* Found junk after ".." */
    } else
	goto bad_modifier;	/* Found junk instead of ".." */

    /*
     * Now first and last are properly filled in, but we still have to check
     * for 0 as a special case.
     */
    if (first == 0 && last == 0) {
	/* ":[0]" or perhaps ":[0..0]" */
	st->oneBigWord = TRUE;
	st->newVal = st->val;
	goto ok;
    }

    /* ":[0..N]" or ":[N..0]" */
    if (first == 0 || last == 0)
	goto bad_modifier;

    /* Normal case: select the words described by first and last. */
    st->newVal = VarSelectWords(st->sep, st->oneBigWord, st->val, first, last);

ok:
    free(estr);
    return AMR_OK;

bad_modifier:
    free(estr);
    return AMR_BAD;
}

static int
str_cmp_asc(const void *a, const void *b)
{
    return strcmp(*(const char * const *)a, *(const char * const *)b);
}

static int
str_cmp_desc(const void *a, const void *b)
{
    return strcmp(*(const char * const *)b, *(const char * const *)a);
}

/* :O (order ascending) or :Or (order descending) or :Ox (shuffle) */
static ApplyModifierResult
ApplyModifier_Order(const char **pp, ApplyModifiersState *st)
{
    const char *mod = (*pp)++;	/* skip past the 'O' in any case */

    Words words = Str_Words(st->val, FALSE);

    if (mod[1] == st->endc || mod[1] == ':') {
	/* :O sorts ascending */
	qsort(words.words, words.len, sizeof words.words[0], str_cmp_asc);

    } else if ((mod[1] == 'r' || mod[1] == 'x') &&
	       (mod[2] == st->endc || mod[2] == ':')) {
	(*pp)++;

	if (mod[1] == 'r') {
	    /* :Or sorts descending */
	    qsort(words.words, words.len, sizeof words.words[0], str_cmp_desc);

	} else {
	    /* :Ox shuffles
	     *
	     * We will use [ac..2] range for mod factors. This will produce
	     * random numbers in [(ac-1)..0] interval, and minimal
	     * reasonable value for mod factor is 2 (the mod 1 will produce
	     * 0 with probability 1).
	     */
	    size_t i;
	    for (i = words.len - 1; i > 0; i--) {
		size_t rndidx = (size_t)random() % (i + 1);
		char *t = words.words[i];
		words.words[i] = words.words[rndidx];
		words.words[rndidx] = t;
	    }
	}
    } else {
	Words_Free(words);
	return AMR_BAD;
    }

    st->newVal = Words_JoinFree(words);
    return AMR_OK;
}

/* :? then : else */
static ApplyModifierResult
ApplyModifier_IfElse(const char **pp, ApplyModifiersState *st)
{
    char *then_expr, *else_expr;
    VarParseResult res;

    Boolean value = FALSE;
    VarEvalFlags then_eflags = VARE_NONE;
    VarEvalFlags else_eflags = VARE_NONE;

    int cond_rc = COND_PARSE;	/* anything other than COND_INVALID */
    if (st->eflags & VARE_WANTRES) {
	cond_rc = Cond_EvalCondition(st->var->name, &value);
	if (cond_rc != COND_INVALID && value)
	    then_eflags = st->eflags;
	if (cond_rc != COND_INVALID && !value)
	    else_eflags = st->eflags;
    }

    (*pp)++;			/* skip past the '?' */
    res = ParseModifierPart(pp, ':', then_eflags, st,
			    &then_expr, NULL, NULL, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;

    res = ParseModifierPart(pp, st->endc, else_eflags, st,
			    &else_expr, NULL, NULL, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;

    (*pp)--;
    if (cond_rc == COND_INVALID) {
	Error("Bad conditional expression `%s' in %s?%s:%s",
	      st->var->name, st->var->name, then_expr, else_expr);
	return AMR_CLEANUP;
    }

    if (value) {
	st->newVal = then_expr;
	free(else_expr);
    } else {
	st->newVal = else_expr;
	free(then_expr);
    }
    ApplyModifiersState_Define(st);
    return AMR_OK;
}

/*
 * The ::= modifiers actually assign a value to the variable.
 * Their main purpose is in supporting modifiers of .for loop
 * iterators and other obscure uses.  They always expand to
 * nothing.  In a target rule that would otherwise expand to an
 * empty line they can be preceded with @: to keep make happy.
 * Eg.
 *
 * foo:	.USE
 * .for i in ${.TARGET} ${.TARGET:R}.gz
 *	@: ${t::=$i}
 *	@echo blah ${t:T}
 * .endfor
 *
 *	  ::=<str>	Assigns <str> as the new value of variable.
 *	  ::?=<str>	Assigns <str> as value of variable if
 *			it was not already set.
 *	  ::+=<str>	Appends <str> to variable.
 *	  ::!=<cmd>	Assigns output of <cmd> as the new value of
 *			variable.
 */
static ApplyModifierResult
ApplyModifier_Assign(const char **pp, ApplyModifiersState *st)
{
    GNode *v_ctxt;
    char delim;
    char *val;
    VarParseResult res;

    const char *mod = *pp;
    const char *op = mod + 1;

    if (op[0] == '=')
	goto ok;
    if ((op[0] == '!' || op[0] == '+' || op[0] == '?') && op[1] == '=')
	goto ok;
    return AMR_UNKNOWN;		/* "::<unrecognised>" */
ok:

    if (st->var->name[0] == '\0') {
	*pp = mod + 1;
	return AMR_BAD;
    }

    v_ctxt = st->ctxt;		/* context where v belongs */
    if (!(st->exprFlags & VEF_UNDEF) && st->ctxt != VAR_GLOBAL) {
	Var *gv = VarFind(st->var->name, st->ctxt, FALSE);
	if (gv == NULL)
	    v_ctxt = VAR_GLOBAL;
	else
	    VarFreeEnv(gv, TRUE);
    }

    switch (op[0]) {
    case '+':
    case '?':
    case '!':
	*pp = mod + 3;
	break;
    default:
	*pp = mod + 2;
	break;
    }

    delim = st->startc == '(' ? ')' : '}';
    res = ParseModifierPart(pp, delim, st->eflags, st, &val, NULL, NULL, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;

    (*pp)--;

    if (st->eflags & VARE_WANTRES) {
	switch (op[0]) {
	case '+':
	    Var_Append(st->var->name, val, v_ctxt);
	    break;
	case '!': {
	    const char *errfmt;
	    char *cmd_output = Cmd_Exec(val, &errfmt);
	    if (errfmt)
		Error(errfmt, val);
	    else
		Var_Set(st->var->name, cmd_output, v_ctxt);
	    free(cmd_output);
	    break;
	}
	case '?':
	    if (!(st->exprFlags & VEF_UNDEF))
		break;
	    /* FALLTHROUGH */
	default:
	    Var_Set(st->var->name, val, v_ctxt);
	    break;
	}
    }
    free(val);
    st->newVal = bmake_strdup("");
    return AMR_OK;
}

/* :_=...
 * remember current value */
static ApplyModifierResult
ApplyModifier_Remember(const char **pp, ApplyModifiersState *st)
{
    const char *mod = *pp;
    if (!ModMatchEq(mod, "_", st->endc))
	return AMR_UNKNOWN;

    if (mod[1] == '=') {
	size_t n = strcspn(mod + 2, ":)}");
	char *name = bmake_strldup(mod + 2, n);
	Var_Set(name, st->val, st->ctxt);
	free(name);
	*pp = mod + 2 + n;
    } else {
	Var_Set("_", st->val, st->ctxt);
	*pp = mod + 1;
    }
    st->newVal = st->val;
    return AMR_OK;
}

/* Apply the given function to each word of the variable value,
 * for a single-letter modifier such as :H, :T. */
static ApplyModifierResult
ApplyModifier_WordFunc(const char **pp, ApplyModifiersState *st,
		       ModifyWordsCallback modifyWord)
{
    char delim = (*pp)[1];
    if (delim != st->endc && delim != ':')
	return AMR_UNKNOWN;

    st->newVal = ModifyWords(st->val, modifyWord, NULL,
			     st->oneBigWord, st->sep);
    (*pp)++;
    return AMR_OK;
}

static ApplyModifierResult
ApplyModifier_Unique(const char **pp, ApplyModifiersState *st)
{
    if ((*pp)[1] == st->endc || (*pp)[1] == ':') {
	st->newVal = VarUniq(st->val);
	(*pp)++;
	return AMR_OK;
    } else
	return AMR_UNKNOWN;
}

#ifdef SYSVVARSUB
/* :from=to */
static ApplyModifierResult
ApplyModifier_SysV(const char **pp, ApplyModifiersState *st)
{
    char *lhs, *rhs;
    VarParseResult res;

    const char *mod = *pp;
    Boolean eqFound = FALSE;

    /*
     * First we make a pass through the string trying to verify it is a
     * SysV-make-style translation. It must be: <lhs>=<rhs>
     */
    int depth = 1;
    const char *p = mod;
    while (*p != '\0' && depth > 0) {
	if (*p == '=') {	/* XXX: should also test depth == 1 */
	    eqFound = TRUE;
	    /* continue looking for st->endc */
	} else if (*p == st->endc)
	    depth--;
	else if (*p == st->startc)
	    depth++;
	if (depth > 0)
	    p++;
    }
    if (*p != st->endc || !eqFound)
	return AMR_UNKNOWN;

    *pp = mod;
    res = ParseModifierPart(pp, '=', st->eflags, st,
			    &lhs, NULL, NULL, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;

    /* The SysV modifier lasts until the end of the variable expression. */
    res = ParseModifierPart(pp, st->endc, st->eflags, st,
			    &rhs, NULL, NULL, NULL);
    if (res != VPR_OK)
	return AMR_CLEANUP;

    (*pp)--;
    if (lhs[0] == '\0' && st->val[0] == '\0') {
	st->newVal = st->val;	/* special case */
    } else {
	struct ModifyWord_SYSVSubstArgs args = {st->ctxt, lhs, rhs};
	st->newVal = ModifyWords(st->val, ModifyWord_SYSVSubst, &args,
				 st->oneBigWord, st->sep);
    }
    free(lhs);
    free(rhs);
    return AMR_OK;
}
#endif

#ifdef SUNSHCMD
/* :sh */
static ApplyModifierResult
ApplyModifier_SunShell(const char **pp, ApplyModifiersState *st)
{
    const char *p = *pp;
    if (p[1] == 'h' && (p[2] == st->endc || p[2] == ':')) {
	if (st->eflags & VARE_WANTRES) {
	    const char *errfmt;
	    st->newVal = Cmd_Exec(st->val, &errfmt);
	    if (errfmt)
		Error(errfmt, st->val);
	} else
	    st->newVal = bmake_strdup("");
	*pp = p + 2;
	return AMR_OK;
    } else
	return AMR_UNKNOWN;
}
#endif

static void
LogBeforeApply(const ApplyModifiersState *st, const char *mod, const char endc)
{
    char eflags_str[VarEvalFlags_ToStringSize];
    char vflags_str[VarFlags_ToStringSize];
    char exprflags_str[VarExprFlags_ToStringSize];
    Boolean is_single_char = mod[0] != '\0' &&
			     (mod[1] == endc || mod[1] == ':');

    /* At this point, only the first character of the modifier can
     * be used since the end of the modifier is not yet known. */
    debug_printf("Applying ${%s:%c%s} to \"%s\" (%s, %s, %s)\n",
		 st->var->name, mod[0], is_single_char ? "" : "...", st->val,
		 Enum_FlagsToString(eflags_str, sizeof eflags_str,
				    st->eflags, VarEvalFlags_ToStringSpecs),
		 Enum_FlagsToString(vflags_str, sizeof vflags_str,
				    st->var->flags, VarFlags_ToStringSpecs),
		 Enum_FlagsToString(exprflags_str, sizeof exprflags_str,
				    st->exprFlags,
				    VarExprFlags_ToStringSpecs));
}

static void
LogAfterApply(ApplyModifiersState *st, const char *p, const char *mod)
{
    char eflags_str[VarEvalFlags_ToStringSize];
    char vflags_str[VarFlags_ToStringSize];
    char exprflags_str[VarExprFlags_ToStringSize];
    const char *quot = st->newVal == var_Error ? "" : "\"";
    const char *newVal = st->newVal == var_Error ? "error" : st->newVal;

    debug_printf("Result of ${%s:%.*s} is %s%s%s (%s, %s, %s)\n",
		 st->var->name, (int)(p - mod), mod, quot, newVal, quot,
		 Enum_FlagsToString(eflags_str, sizeof eflags_str,
				    st->eflags, VarEvalFlags_ToStringSpecs),
		 Enum_FlagsToString(vflags_str, sizeof vflags_str,
				    st->var->flags, VarFlags_ToStringSpecs),
		 Enum_FlagsToString(exprflags_str, sizeof exprflags_str,
				    st->exprFlags,
				    VarExprFlags_ToStringSpecs));
}

static ApplyModifierResult
ApplyModifier(const char **pp, ApplyModifiersState *st)
{
    switch (**pp) {
    case ':':
	return ApplyModifier_Assign(pp, st);
    case '@':
	return ApplyModifier_Loop(pp, st);
    case '_':
	return ApplyModifier_Remember(pp, st);
    case 'D':
    case 'U':
	return ApplyModifier_Defined(pp, st);
    case 'L':
	return ApplyModifier_Literal(pp, st);
    case 'P':
	return ApplyModifier_Path(pp, st);
    case '!':
	return ApplyModifier_ShellCommand(pp, st);
    case '[':
	return ApplyModifier_Words(pp, st);
    case 'g':
	return ApplyModifier_Gmtime(pp, st);
    case 'h':
	return ApplyModifier_Hash(pp, st);
    case 'l':
	return ApplyModifier_Localtime(pp, st);
    case 't':
	return ApplyModifier_To(pp, st);
    case 'N':
    case 'M':
	return ApplyModifier_Match(pp, st);
    case 'S':
	return ApplyModifier_Subst(pp, st);
    case '?':
	return ApplyModifier_IfElse(pp, st);
#ifndef NO_REGEX
    case 'C':
	return ApplyModifier_Regex(pp, st);
#endif
    case 'q':
    case 'Q':
	return ApplyModifier_Quote(pp, st);
    case 'T':
	return ApplyModifier_WordFunc(pp, st, ModifyWord_Tail);
    case 'H':
	return ApplyModifier_WordFunc(pp, st, ModifyWord_Head);
    case 'E':
	return ApplyModifier_WordFunc(pp, st, ModifyWord_Suffix);
    case 'R':
	return ApplyModifier_WordFunc(pp, st, ModifyWord_Root);
    case 'r':
	return ApplyModifier_Range(pp, st);
    case 'O':
	return ApplyModifier_Order(pp, st);
    case 'u':
	return ApplyModifier_Unique(pp, st);
#ifdef SUNSHCMD
    case 's':
	return ApplyModifier_SunShell(pp, st);
#endif
    default:
	return AMR_UNKNOWN;
    }
}

static char *ApplyModifiers(const char **, char *, char, char, Var *,
			    VarExprFlags *, GNode *, VarEvalFlags, void **);

typedef enum ApplyModifiersIndirectResult {
    AMIR_CONTINUE,
    AMIR_APPLY_MODS,
    AMIR_OUT
} ApplyModifiersIndirectResult;

/* While expanding a variable expression, expand and apply indirect
 * modifiers such as in ${VAR:${M_indirect}}. */
static ApplyModifiersIndirectResult
ApplyModifiersIndirect(
	ApplyModifiersState *const st,
	const char **const inout_p,
	void **const inout_freeIt
) {
    const char *p = *inout_p;
    const char *mods;
    void *mods_freeIt;

    (void)Var_Parse(&p, st->ctxt, st->eflags, &mods, &mods_freeIt);
    /* TODO: handle errors */

    /*
     * If we have not parsed up to st->endc or ':', we are not
     * interested.  This means the expression ${VAR:${M_1}${M_2}}
     * is not accepted, but ${VAR:${M_1}:${M_2}} is.
     */
    if (mods[0] != '\0' && *p != '\0' && *p != ':' && *p != st->endc) {
	if (opts.lint)
	    Parse_Error(PARSE_FATAL,
			"Missing delimiter ':' after indirect modifier \"%.*s\"",
			(int)(p - *inout_p), *inout_p);

	free(mods_freeIt);
	/* XXX: apply_mods doesn't sound like "not interested". */
	/* XXX: Why is the indirect modifier parsed once more by
	 * apply_mods?  If any, p should be advanced to nested_p. */
	return AMIR_APPLY_MODS;
    }

    VAR_DEBUG3("Indirect modifier \"%s\" from \"%.*s\"\n",
	       mods, (int)(p - *inout_p), *inout_p);

    if (mods[0] != '\0') {
	const char *rval_pp = mods;
	st->val = ApplyModifiers(&rval_pp, st->val, '\0', '\0', st->var,
				 &st->exprFlags, st->ctxt, st->eflags,
				 inout_freeIt);
	if (st->val == var_Error || st->val == varUndefined ||
	    *rval_pp != '\0') {
	    free(mods_freeIt);
	    *inout_p = p;
	    return AMIR_OUT;	/* error already reported */
	}
    }
    free(mods_freeIt);

    if (*p == ':')
	p++;
    else if (*p == '\0' && st->endc != '\0') {
	Error("Unclosed variable specification after complex "
	      "modifier (expecting '%c') for %s", st->endc, st->var->name);
	*inout_p = p;
	return AMIR_OUT;
    }

    *inout_p = p;
    return AMIR_CONTINUE;
}

/* Apply any modifiers (such as :Mpattern or :@var@loop@ or :Q or ::=value). */
static char *
ApplyModifiers(
    const char **const pp,	/* the parsing position, updated upon return */
    char *const val,		/* the current value of the expression */
    char const startc,		/* '(' or '{', or '\0' for indirect modifiers */
    char const endc,		/* ')' or '}', or '\0' for indirect modifiers */
    Var *const v,
    VarExprFlags *const exprFlags,
    GNode *const ctxt,		/* for looking up and modifying variables */
    VarEvalFlags const eflags,
    void **const inout_freeIt	/* free this after using the return value */
) {
    ApplyModifiersState st = {
	startc, endc, v, ctxt, eflags,
	val,			/* .val */
	var_Error,		/* .newVal */
	' ',			/* .sep */
	FALSE,			/* .oneBigWord */
	*exprFlags		/* .exprFlags */
    };
    const char *p;
    const char *mod;
    ApplyModifierResult res;

    assert(startc == '(' || startc == '{' || startc == '\0');
    assert(endc == ')' || endc == '}' || endc == '\0');
    assert(val != NULL);

    p = *pp;

    if (*p == '\0' && endc != '\0') {
	Error("Unclosed variable expression (expecting '%c') for \"%s\"",
	      st.endc, st.var->name);
	goto cleanup;
    }

    while (*p != '\0' && *p != endc) {

	if (*p == '$') {
	    ApplyModifiersIndirectResult amir;
	    amir = ApplyModifiersIndirect(&st, &p, inout_freeIt);
	    if (amir == AMIR_CONTINUE)
		continue;
	    if (amir == AMIR_OUT)
	        goto out;
	}
	st.newVal = var_Error;	/* default value, in case of errors */
	mod = p;

	if (DEBUG(VAR))
	    LogBeforeApply(&st, mod, endc);

	res = ApplyModifier(&p, &st);

#ifdef SYSVVARSUB
	if (res == AMR_UNKNOWN) {
	    assert(p == mod);
	    res = ApplyModifier_SysV(&p, &st);
	}
#endif

	if (res == AMR_UNKNOWN) {
	    Error("Unknown modifier '%c'", *mod);
	    /* Guess the end of the current modifier.
	     * XXX: Skipping the rest of the modifier hides errors and leads
	     * to wrong results.  Parsing should rather stop here. */
	    for (p++; *p != ':' && *p != st.endc && *p != '\0'; p++)
		continue;
	    st.newVal = var_Error;
	}
	if (res == AMR_CLEANUP)
	    goto cleanup;
	if (res == AMR_BAD)
	    goto bad_modifier;

	if (DEBUG(VAR))
	    LogAfterApply(&st, p, mod);

	if (st.newVal != st.val) {
	    if (*inout_freeIt != NULL) {
		free(st.val);
		*inout_freeIt = NULL;
	    }
	    st.val = st.newVal;
	    if (st.val != var_Error && st.val != varUndefined)
		*inout_freeIt = st.val;
	}
	if (*p == '\0' && st.endc != '\0') {
	    Error("Unclosed variable specification (expecting '%c') "
		  "for \"%s\" (value \"%s\") modifier %c",
		  st.endc, st.var->name, st.val, *mod);
	} else if (*p == ':') {
	    p++;
	} else if (opts.lint && *p != '\0' && *p != endc) {
	    Parse_Error(PARSE_FATAL,
			"Missing delimiter ':' after modifier \"%.*s\"",
			(int)(p - mod), mod);
	    /* TODO: propagate parse error to the enclosing expression */
	}
    }
out:
    *pp = p;
    assert(st.val != NULL);	/* Use var_Error or varUndefined instead. */
    *exprFlags = st.exprFlags;
    return st.val;

bad_modifier:
    /* XXX: The modifier end is only guessed. */
    Error("Bad modifier `:%.*s' for %s",
	  (int)strcspn(mod, ":)}"), mod, st.var->name);

cleanup:
    *pp = p;
    free(*inout_freeIt);
    *inout_freeIt = NULL;
    *exprFlags = st.exprFlags;
    return var_Error;
}

/* Only four of the local variables are treated specially as they are the
 * only four that will be set when dynamic sources are expanded. */
static Boolean
VarnameIsDynamic(const char *name, size_t len)
{
    if (len == 1 || (len == 2 && (name[1] == 'F' || name[1] == 'D'))) {
	switch (name[0]) {
	case '@':
	case '%':
	case '*':
	case '!':
	    return TRUE;
	}
	return FALSE;
    }

    if ((len == 7 || len == 8) && name[0] == '.' && ch_isupper(name[1])) {
	return strcmp(name, ".TARGET") == 0 ||
	       strcmp(name, ".ARCHIVE") == 0 ||
	       strcmp(name, ".PREFIX") == 0 ||
	       strcmp(name, ".MEMBER") == 0;
    }

    return FALSE;
}

static const char *
UndefinedShortVarValue(char varname, const GNode *ctxt, VarEvalFlags eflags)
{
    if (ctxt == VAR_CMDLINE || ctxt == VAR_GLOBAL) {
	/*
	 * If substituting a local variable in a non-local context,
	 * assume it's for dynamic source stuff. We have to handle
	 * this specially and return the longhand for the variable
	 * with the dollar sign escaped so it makes it back to the
	 * caller. Only four of the local variables are treated
	 * specially as they are the only four that will be set
	 * when dynamic sources are expanded.
	 */
	switch (varname) {
	case '@':
	    return "$(.TARGET)";
	case '%':
	    return "$(.MEMBER)";
	case '*':
	    return "$(.PREFIX)";
	case '!':
	    return "$(.ARCHIVE)";
	}
    }
    return eflags & VARE_UNDEFERR ? var_Error : varUndefined;
}

/* Parse a variable name, until the end character or a colon, whichever
 * comes first. */
static char *
ParseVarname(const char **pp, char startc, char endc,
	     GNode *ctxt, VarEvalFlags eflags,
	     size_t *out_varname_len)
{
    Buffer buf;
    const char *p = *pp;
    int depth = 1;

    Buf_Init(&buf);

    while (*p != '\0') {
	/* Track depth so we can spot parse errors. */
	if (*p == startc)
	    depth++;
	if (*p == endc) {
	    if (--depth == 0)
		break;
	}
	if (*p == ':' && depth == 1)
	    break;

	/* A variable inside a variable, expand. */
	if (*p == '$') {
	    const char *nested_val;
	    void *nested_val_freeIt;
	    (void)Var_Parse(&p, ctxt, eflags, &nested_val, &nested_val_freeIt);
	    /* TODO: handle errors */
	    Buf_AddStr(&buf, nested_val);
	    free(nested_val_freeIt);
	} else {
	    Buf_AddByte(&buf, *p);
	    p++;
	}
    }
    *pp = p;
    *out_varname_len = Buf_Len(&buf);
    return Buf_Destroy(&buf, FALSE);
}

static VarParseResult
ValidShortVarname(char varname, const char *start)
{
    switch (varname) {
    case '\0':
    case ')':
    case '}':
    case ':':
    case '$':
	break;			/* and continue below */
    default:
	return VPR_OK;
    }

    if (!opts.lint)
	return VPR_PARSE_SILENT;

    if (varname == '$')
	Parse_Error(PARSE_FATAL,
		    "To escape a dollar, use \\$, not $$, at \"%s\"", start);
    else if (varname == '\0')
	Parse_Error(PARSE_FATAL, "Dollar followed by nothing");
    else
	Parse_Error(PARSE_FATAL,
		    "Invalid variable name '%c', at \"%s\"", varname, start);

    return VPR_PARSE_MSG;
}

/* Parse a single-character variable name such as $V or $@.
 * Return whether to continue parsing. */
static Boolean
ParseVarnameShort(char startc, const char **pp, GNode *ctxt,
		  VarEvalFlags eflags,
		  VarParseResult *out_FALSE_res, const char **out_FALSE_val,
		  Var **out_TRUE_var)
{
    char name[2];
    Var *v;
    VarParseResult vpr;

    /*
     * If it's not bounded by braces of some sort, life is much simpler.
     * We just need to check for the first character and return the
     * value if it exists.
     */

    vpr = ValidShortVarname(startc, *pp);
    if (vpr != VPR_OK) {
	(*pp)++;
	*out_FALSE_val = var_Error;
	*out_FALSE_res = vpr;
	return FALSE;
    }

    name[0] = startc;
    name[1] = '\0';
    v = VarFind(name, ctxt, TRUE);
    if (v == NULL) {
	*pp += 2;

	*out_FALSE_val = UndefinedShortVarValue(startc, ctxt, eflags);
	if (opts.lint && *out_FALSE_val == var_Error) {
	    Parse_Error(PARSE_FATAL, "Variable \"%s\" is undefined", name);
	    *out_FALSE_res = VPR_UNDEF_MSG;
	    return FALSE;
	}
	*out_FALSE_res = eflags & VARE_UNDEFERR ? VPR_UNDEF_SILENT : VPR_OK;
	return FALSE;
    }

    *out_TRUE_var = v;
    return TRUE;
}

/* Find variables like @F or <D. */
static Var *
FindLocalLegacyVar(const char *varname, size_t namelen, GNode *ctxt,
		   const char **out_extraModifiers)
{
    /* Only resolve these variables if ctxt is a "real" target. */
    if (ctxt == VAR_CMDLINE || ctxt == VAR_GLOBAL)
	return NULL;

    if (namelen != 2)
	return NULL;
    if (varname[1] != 'F' && varname[1] != 'D')
	return NULL;
    if (strchr("@%?*!<>", varname[0]) == NULL)
	return NULL;

    {
	char name[] = { varname[0], '\0' };
	Var *v = VarFind(name, ctxt, FALSE);

	if (v != NULL) {
	    if (varname[1] == 'D') {
		*out_extraModifiers = "H:";
	    } else { /* F */
		*out_extraModifiers = "T:";
	    }
	}
	return v;
    }
}

static VarParseResult
EvalUndefined(Boolean dynamic, const char *start, const char *p, char *varname,
	      VarEvalFlags eflags,
	      void **out_freeIt, const char **out_val)
{
    if (dynamic) {
	char *pstr = bmake_strsedup(start, p);
	free(varname);
	*out_freeIt = pstr;
	*out_val = pstr;
	return VPR_OK;
    }

    if ((eflags & VARE_UNDEFERR) && opts.lint) {
	Parse_Error(PARSE_FATAL, "Variable \"%s\" is undefined", varname);
	free(varname);
	*out_val = var_Error;
	return VPR_UNDEF_MSG;
    }

    if (eflags & VARE_UNDEFERR) {
	free(varname);
	*out_val = var_Error;
	return VPR_UNDEF_SILENT;
    }

    free(varname);
    *out_val = varUndefined;
    return VPR_OK;
}

/* Parse a long variable name enclosed in braces or parentheses such as $(VAR)
 * or ${VAR}, up to the closing brace or parenthesis, or in the case of
 * ${VAR:Modifiers}, up to the ':' that starts the modifiers.
 * Return whether to continue parsing. */
static Boolean
ParseVarnameLong(
	const char *p,
	char startc,
	GNode *ctxt,
	VarEvalFlags eflags,

	const char **out_FALSE_pp,
	VarParseResult *out_FALSE_res,
	const char **out_FALSE_val,
	void **out_FALSE_freeIt,

	char *out_TRUE_endc,
	const char **out_TRUE_p,
	Var **out_TRUE_v,
	Boolean *out_TRUE_haveModifier,
	const char **out_TRUE_extraModifiers,
	Boolean *out_TRUE_dynamic,
	VarExprFlags *out_TRUE_exprFlags
) {
    size_t namelen;
    char *varname;
    Var *v;
    Boolean haveModifier;
    Boolean dynamic = FALSE;

    const char *const start = p;
    char endc = startc == '(' ? ')' : '}';

    p += 2;			/* skip "${" or "$(" or "y(" */
    varname = ParseVarname(&p, startc, endc, ctxt, eflags, &namelen);

    if (*p == ':') {
	haveModifier = TRUE;
    } else if (*p == endc) {
	haveModifier = FALSE;
    } else {
	Parse_Error(PARSE_FATAL, "Unclosed variable \"%s\"", varname);
	free(varname);
	*out_FALSE_pp = p;
	*out_FALSE_val = var_Error;
	*out_FALSE_res = VPR_PARSE_MSG;
	return FALSE;
    }

    v = VarFind(varname, ctxt, TRUE);

    /* At this point, p points just after the variable name,
     * either at ':' or at endc. */

    if (v == NULL)
	v = FindLocalLegacyVar(varname, namelen, ctxt, out_TRUE_extraModifiers);

    if (v == NULL) {
	/* Defer expansion of dynamic variables if they appear in non-local
	 * context since they are not defined there. */
	dynamic = VarnameIsDynamic(varname, namelen) &&
		  (ctxt == VAR_CMDLINE || ctxt == VAR_GLOBAL);

	if (!haveModifier) {
	    p++;		/* skip endc */
	    *out_FALSE_pp = p;
	    *out_FALSE_res = EvalUndefined(dynamic, start, p, varname, eflags,
					   out_FALSE_freeIt, out_FALSE_val);
	    return FALSE;
	}

	/* The variable expression is based on an undefined variable.
	 * Nevertheless it needs a Var, for modifiers that access the
	 * variable name, such as :L or :?.
	 *
	 * Most modifiers leave this expression in the "undefined" state
	 * (VEF_UNDEF), only a few modifiers like :D, :U, :L, :P turn this
	 * undefined expression into a defined expression (VEF_DEF).
	 *
	 * At the end, after applying all modifiers, if the expression
	 * is still undefined, Var_Parse will return an empty string
	 * instead of the actually computed value. */
	v = VarNew(varname, varname, "", 0);
	*out_TRUE_exprFlags = VEF_UNDEF;
    } else
	free(varname);

    *out_TRUE_endc = endc;
    *out_TRUE_p = p;
    *out_TRUE_v = v;
    *out_TRUE_haveModifier = haveModifier;
    *out_TRUE_dynamic = dynamic;
    return TRUE;
}

/*
 * Given the start of a variable expression (such as $v, $(VAR),
 * ${VAR:Mpattern}), extract the variable name and value, and the modifiers,
 * if any.  While doing that, apply the modifiers to the value of the
 * expression, forming its final value.  A few of the modifiers such as :!cmd!
 * or ::= have side effects.
 *
 * Input:
 *	*pp		The string to parse.
 *			When parsing a condition in ParseEmptyArg, it may also
 *			point to the "y" of "empty(VARNAME:Modifiers)", which
 *			is syntactically the same.
 *	ctxt		The context for finding variables
 *	eflags		Control the exact details of parsing
 *
 * Output:
 *	*pp		The position where to continue parsing.
 *			TODO: After a parse error, the value of *pp is
 *			unspecified.  It may not have been updated at all,
 *			point to some random character in the string, to the
 *			location of the parse error, or at the end of the
 *			string.
 *	*out_val	The value of the variable expression, never NULL.
 *	*out_val	var_Error if there was a parse error.
 *	*out_val	var_Error if the base variable of the expression was
 *			undefined, eflags contains VARE_UNDEFERR, and none of
 *			the modifiers turned the undefined expression into a
 *			defined expression.
 *			XXX: It is not guaranteed that an error message has
 *			been printed.
 *	*out_val	varUndefined if the base variable of the expression
 *			was undefined, eflags did not contain VARE_UNDEFERR,
 *			and none of the modifiers turned the undefined
 *			expression into a defined expression.
 *			XXX: It is not guaranteed that an error message has
 *			been printed.
 *	*out_val_freeIt	Must be freed by the caller after using *out_val.
 */
/* coverity[+alloc : arg-*4] */
VarParseResult
Var_Parse(const char **pp, GNode *ctxt, VarEvalFlags eflags,
	  const char **out_val, void **out_val_freeIt)
{
    const char *p = *pp;
    const char *const start = p;
    Boolean haveModifier;	/* TRUE if have modifiers for the variable */
    char startc;		/* Starting character if variable in parens
				 * or braces */
    char endc;			/* Ending character if variable in parens
				 * or braces */
    Boolean dynamic;		/* TRUE if the variable is local and we're
				 * expanding it in a non-local context. This
				 * is done to support dynamic sources. The
				 * result is just the expression, unaltered */
    const char *extramodifiers;
    Var *v;
    char *value;
    char eflags_str[VarEvalFlags_ToStringSize];
    VarExprFlags exprFlags = 0;

    VAR_DEBUG2("Var_Parse: %s with %s\n", start,
	       Enum_FlagsToString(eflags_str, sizeof eflags_str, eflags,
				  VarEvalFlags_ToStringSpecs));

    *out_val_freeIt = NULL;
    extramodifiers = NULL;	/* extra modifiers to apply first */
    dynamic = FALSE;

    /* Appease GCC, which thinks that the variable might not be
     * initialized. */
    endc = '\0';

    startc = p[1];
    if (startc != '(' && startc != '{') {
	VarParseResult res;
	if (!ParseVarnameShort(startc, pp, ctxt, eflags, &res, out_val, &v))
	    return res;
	haveModifier = FALSE;
	p++;
    } else {
	VarParseResult res;
	if (!ParseVarnameLong(p, startc, ctxt, eflags,
			      pp, &res, out_val, out_val_freeIt,
			      &endc, &p, &v, &haveModifier, &extramodifiers,
			      &dynamic, &exprFlags))
	    return res;
    }

    if (v->flags & VAR_IN_USE)
	Fatal("Variable %s is recursive.", v->name);

    /* XXX: This assignment creates an alias to the current value of the
     * variable.  This means that as long as the value of the expression stays
     * the same, the value of the variable must not change.
     * Using the '::=' modifier, it could be possible to do exactly this.
     * At the bottom of this function, the resulting value is compared to the
     * then-current value of the variable.  This might also invoke undefined
     * behavior. */
    value = Buf_GetAll(&v->val, NULL);

    /* Before applying any modifiers, expand any nested expressions from the
     * variable value. */
    if (strchr(value, '$') != NULL && (eflags & VARE_WANTRES)) {
	VarEvalFlags nested_eflags = eflags;
	if (opts.lint)
	    nested_eflags &= ~(unsigned)VARE_UNDEFERR;
	v->flags |= VAR_IN_USE;
	(void)Var_Subst(value, ctxt, nested_eflags, &value);
	v->flags &= ~(unsigned)VAR_IN_USE;
	/* TODO: handle errors */
	*out_val_freeIt = value;
    }

    if (haveModifier || extramodifiers != NULL) {
	void *extraFree;

	extraFree = NULL;
	if (extramodifiers != NULL) {
	    const char *em = extramodifiers;
	    value = ApplyModifiers(&em, value, '\0', '\0',
				   v, &exprFlags, ctxt, eflags, &extraFree);
	}

	if (haveModifier) {
	    /* Skip initial colon. */
	    p++;

	    value = ApplyModifiers(&p, value, startc, endc,
				   v, &exprFlags, ctxt, eflags, out_val_freeIt);
	    free(extraFree);
	} else {
	    *out_val_freeIt = extraFree;
	}
    }

    if (*p != '\0')		/* Skip past endc if possible. */
	p++;

    *pp = p;

    if (v->flags & VAR_FROM_ENV) {
	/* Free the environment variable now since we own it,
	 * but don't free the variable value if it will be returned. */
	Boolean keepValue = value == Buf_GetAll(&v->val, NULL);
	if (keepValue)
	    *out_val_freeIt = value;
	(void)VarFreeEnv(v, !keepValue);

    } else if (exprFlags & VEF_UNDEF) {
	if (!(exprFlags & VEF_DEF)) {
	    /* TODO: Use a local variable instead of out_val_freeIt.
	     * Variables named out_* must only be written to. */
	    if (*out_val_freeIt != NULL) {
		free(*out_val_freeIt);
		*out_val_freeIt = NULL;
	    }
	    if (dynamic) {
		value = bmake_strsedup(start, p);
		*out_val_freeIt = value;
	    } else {
		/* The expression is still undefined, therefore discard the
		 * actual value and return an error marker instead. */
		value = eflags & VARE_UNDEFERR ? var_Error : varUndefined;
	    }
	}
	if (value != Buf_GetAll(&v->val, NULL))
	    Buf_Destroy(&v->val, TRUE);
	free(v->name_freeIt);
	free(v);
    }
    *out_val = value;
    return VPR_UNKNOWN;
}

static void
VarSubstNested(const char **const pp, Buffer *const buf, GNode *const ctxt,
	       VarEvalFlags const eflags, Boolean *inout_errorReported)
{
    const char *p = *pp;
    const char *nested_p = p;
    const char *val;
    void *val_freeIt;

    (void)Var_Parse(&nested_p, ctxt, eflags, &val, &val_freeIt);
    /* TODO: handle errors */

    if (val == var_Error || val == varUndefined) {
	if (!preserveUndefined) {
	    p = nested_p;
	} else if ((eflags & VARE_UNDEFERR) || val == var_Error) {
	    /* XXX: This condition is wrong.  If val == var_Error,
	     * this doesn't necessarily mean there was an undefined
	     * variable.  It could equally well be a parse error; see
	     * unit-tests/varmod-order.exp. */

	    /*
	     * If variable is undefined, complain and skip the
	     * variable. The complaint will stop us from doing anything
	     * when the file is parsed.
	     */
	    if (!*inout_errorReported) {
		Parse_Error(PARSE_FATAL, "Undefined variable \"%.*s\"",
			    (int)(size_t)(nested_p - p), p);
	    }
	    p = nested_p;
	    *inout_errorReported = TRUE;
	} else {
	    /* Copy the initial '$' of the undefined expression,
	     * thereby deferring expansion of the expression, but
	     * expand nested expressions if already possible.
	     * See unit-tests/varparse-undef-partial.mk. */
	    Buf_AddByte(buf, *p);
	    p++;
	}
    } else {
	p = nested_p;
	Buf_AddStr(buf, val);
    }

    free(val_freeIt);

    *pp = p;
}

/* Expand all variable expressions like $V, ${VAR}, $(VAR:Modifiers) in the
 * given string.
 *
 * Input:
 *	str		The string in which the variable expressions are
 *			expanded.
 *	ctxt		The context in which to start searching for
 *			variables.  The other contexts are searched as well.
 *	eflags		Special effects during expansion.
 */
VarParseResult
Var_Subst(const char *str, GNode *ctxt, VarEvalFlags eflags, char **out_res)
{
    const char *p = str;
    Buffer buf;			/* Buffer for forming things */

    /* Set true if an error has already been reported,
     * to prevent a plethora of messages when recursing */
    /* XXX: Why is the 'static' necessary here? */
    static Boolean errorReported;

    Buf_Init(&buf);
    errorReported = FALSE;

    while (*p != '\0') {
	if (p[0] == '$' && p[1] == '$') {
	    /* A dollar sign may be escaped with another dollar sign. */
	    if (save_dollars && (eflags & VARE_KEEP_DOLLAR))
		Buf_AddByte(&buf, '$');
	    Buf_AddByte(&buf, '$');
	    p += 2;

	} else if (p[0] == '$') {
	    VarSubstNested(&p, &buf, ctxt, eflags, &errorReported);

	} else {
	    /*
	     * Skip as many characters as possible -- either to the end of
	     * the string or to the next dollar sign (variable expression).
	     */
	    const char *plainStart = p;

	    for (p++; *p != '$' && *p != '\0'; p++)
		continue;
	    Buf_AddBytesBetween(&buf, plainStart, p);
	}
    }

    *out_res = Buf_DestroyCompact(&buf);
    return VPR_OK;
}

/* Initialize the variables module. */
void
Var_Init(void)
{
    VAR_INTERNAL = GNode_New("Internal");
    VAR_GLOBAL = GNode_New("Global");
    VAR_CMDLINE = GNode_New("Command");
}

/* Clean up the variables module. */
void
Var_End(void)
{
    Var_Stats();
}

void
Var_Stats(void)
{
    HashTable_DebugStats(&VAR_GLOBAL->context, "VAR_GLOBAL");
}

/* Print all variables in a context, sorted by name. */
void
Var_Dump(GNode *ctxt)
{
    Vector /* of const char * */ vec;
    HashIter hi;
    size_t i;
    const char **varnames;

    Vector_Init(&vec, sizeof(const char *));

    HashIter_Init(&hi, &ctxt->context);
    while (HashIter_Next(&hi) != NULL)
	*(const char **)Vector_Push(&vec) = hi.entry->key;
    varnames = vec.items;

    qsort(varnames, vec.len, sizeof varnames[0], str_cmp_asc);

    for (i = 0; i < vec.len; i++) {
	const char *varname = varnames[i];
	Var *var = HashTable_FindValue(&ctxt->context, varname);
	debug_printf("%-16s = %s\n", varname, Buf_GetAll(&var->val, NULL));
    }

    Vector_Done(&vec);
}