xref: /llvm-project/flang/lib/Evaluate/check-expression.cpp (revision 0f973ac783aa100cfbce1cd2c6e8a3a8f648fae7) 
1 //===-- lib/Evaluate/check-expression.cpp ---------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "flang/Evaluate/check-expression.h"
10 #include "flang/Evaluate/characteristics.h"
11 #include "flang/Evaluate/intrinsics.h"
12 #include "flang/Evaluate/tools.h"
13 #include "flang/Evaluate/traverse.h"
14 #include "flang/Evaluate/type.h"
15 #include "flang/Semantics/semantics.h"
16 #include "flang/Semantics/symbol.h"
17 #include "flang/Semantics/tools.h"
18 #include <set>
19 #include <string>
20 
21 namespace Fortran::evaluate {
22 
23 // Constant expression predicates IsConstantExpr() & IsScopeInvariantExpr().
24 // This code determines whether an expression is a "constant expression"
25 // in the sense of section 10.1.12.  This is not the same thing as being
26 // able to fold it (yet) into a known constant value; specifically,
27 // the expression may reference derived type kind parameters whose values
28 // are not yet known.
29 //
30 // The variant form (IsScopeInvariantExpr()) also accepts symbols that are
31 // INTENT(IN) dummy arguments without the VALUE attribute.
32 template <bool INVARIANT>
33 class IsConstantExprHelper
34     : public AllTraverse<IsConstantExprHelper<INVARIANT>, true> {
35 public:
36   using Base = AllTraverse<IsConstantExprHelper, true>;
37   IsConstantExprHelper() : Base{*this} {}
38   using Base::operator();
39 
40   // A missing expression is not considered to be constant.
41   template <typename A> bool operator()(const std::optional<A> &x) const {
42     return x && (*this)(*x);
43   }
44 
45   bool operator()(const TypeParamInquiry &inq) const {
46     return INVARIANT || semantics::IsKindTypeParameter(inq.parameter());
47   }
48   bool operator()(const semantics::Symbol &symbol) const {
49     const auto &ultimate{GetAssociationRoot(symbol)};
50     return IsNamedConstant(ultimate) || IsImpliedDoIndex(ultimate) ||
51         IsInitialProcedureTarget(ultimate) ||
52         ultimate.has<semantics::TypeParamDetails>() ||
53         (INVARIANT && IsIntentIn(symbol) && !IsOptional(symbol) &&
54             !symbol.attrs().test(semantics::Attr::VALUE));
55   }
56   bool operator()(const CoarrayRef &) const { return false; }
57   bool operator()(const semantics::ParamValue &param) const {
58     return param.isExplicit() && (*this)(param.GetExplicit());
59   }
60   bool operator()(const ProcedureRef &) const;
61   bool operator()(const StructureConstructor &constructor) const {
62     for (const auto &[symRef, expr] : constructor) {
63       if (!IsConstantStructureConstructorComponent(*symRef, expr.value())) {
64         return false;
65       }
66     }
67     return true;
68   }
69   bool operator()(const Component &component) const {
70     return (*this)(component.base());
71   }
72   // Forbid integer division by zero in constants.
73   template <int KIND>
74   bool operator()(
75       const Divide<Type<TypeCategory::Integer, KIND>> &division) const {
76     using T = Type<TypeCategory::Integer, KIND>;
77     if (const auto divisor{GetScalarConstantValue<T>(division.right())}) {
78       return !divisor->IsZero() && (*this)(division.left());
79     } else {
80       return false;
81     }
82   }
83 
84   bool operator()(const Constant<SomeDerived> &) const { return true; }
85   bool operator()(const DescriptorInquiry &x) const {
86     const Symbol &sym{x.base().GetLastSymbol()};
87     return INVARIANT && !IsAllocatable(sym) &&
88         (!IsDummy(sym) ||
89             (IsIntentIn(sym) && !IsOptional(sym) &&
90                 !sym.attrs().test(semantics::Attr::VALUE)));
91   }
92 
93 private:
94   bool IsConstantStructureConstructorComponent(
95       const Symbol &, const Expr<SomeType> &) const;
96   bool IsConstantExprShape(const Shape &) const;
97 };
98 
99 template <bool INVARIANT>
100 bool IsConstantExprHelper<INVARIANT>::IsConstantStructureConstructorComponent(
101     const Symbol &component, const Expr<SomeType> &expr) const {
102   if (IsAllocatable(component)) {
103     return IsNullObjectPointer(expr);
104   } else if (IsPointer(component)) {
105     return IsNullPointer(expr) || IsInitialDataTarget(expr) ||
106         IsInitialProcedureTarget(expr);
107   } else {
108     return (*this)(expr);
109   }
110 }
111 
112 template <bool INVARIANT>
113 bool IsConstantExprHelper<INVARIANT>::operator()(
114     const ProcedureRef &call) const {
115   // LBOUND, UBOUND, and SIZE with truly constant DIM= arguments will have
116   // been rewritten into DescriptorInquiry operations.
117   if (const auto *intrinsic{std::get_if<SpecificIntrinsic>(&call.proc().u)}) {
118     const characteristics::Procedure &proc{intrinsic->characteristics.value()};
119     if (intrinsic->name == "kind" ||
120         intrinsic->name == IntrinsicProcTable::InvalidName ||
121         call.arguments().empty() || !call.arguments()[0]) {
122       // kind is always a constant, and we avoid cascading errors by considering
123       // invalid calls to intrinsics to be constant
124       return true;
125     } else if (intrinsic->name == "lbound") {
126       auto base{ExtractNamedEntity(call.arguments()[0]->UnwrapExpr())};
127       return base && IsConstantExprShape(GetLBOUNDs(*base));
128     } else if (intrinsic->name == "ubound") {
129       auto base{ExtractNamedEntity(call.arguments()[0]->UnwrapExpr())};
130       return base && IsConstantExprShape(GetUBOUNDs(*base));
131     } else if (intrinsic->name == "shape" || intrinsic->name == "size") {
132       auto shape{GetShape(call.arguments()[0]->UnwrapExpr())};
133       return shape && IsConstantExprShape(*shape);
134     } else if (proc.IsPure()) {
135       for (const auto &arg : call.arguments()) {
136         if (!arg) {
137           return false;
138         } else if (const auto *expr{arg->UnwrapExpr()};
139                    !expr || !(*this)(*expr)) {
140           return false;
141         }
142       }
143       return true;
144     }
145     // TODO: STORAGE_SIZE
146   }
147   return false;
148 }
149 
150 template <bool INVARIANT>
151 bool IsConstantExprHelper<INVARIANT>::IsConstantExprShape(
152     const Shape &shape) const {
153   for (const auto &extent : shape) {
154     if (!(*this)(extent)) {
155       return false;
156     }
157   }
158   return true;
159 }
160 
161 template <typename A> bool IsConstantExpr(const A &x) {
162   return IsConstantExprHelper<false>{}(x);
163 }
164 template bool IsConstantExpr(const Expr<SomeType> &);
165 template bool IsConstantExpr(const Expr<SomeInteger> &);
166 template bool IsConstantExpr(const Expr<SubscriptInteger> &);
167 template bool IsConstantExpr(const StructureConstructor &);
168 
169 // IsScopeInvariantExpr()
170 template <typename A> bool IsScopeInvariantExpr(const A &x) {
171   return IsConstantExprHelper<true>{}(x);
172 }
173 template bool IsScopeInvariantExpr(const Expr<SomeType> &);
174 template bool IsScopeInvariantExpr(const Expr<SomeInteger> &);
175 template bool IsScopeInvariantExpr(const Expr<SubscriptInteger> &);
176 
177 // IsActuallyConstant()
178 struct IsActuallyConstantHelper {
179   template <typename A> bool operator()(const A &) { return false; }
180   template <typename T> bool operator()(const Constant<T> &) { return true; }
181   template <typename T> bool operator()(const Parentheses<T> &x) {
182     return (*this)(x.left());
183   }
184   template <typename T> bool operator()(const Expr<T> &x) {
185     return common::visit([=](const auto &y) { return (*this)(y); }, x.u);
186   }
187   bool operator()(const Expr<SomeType> &x) {
188     return common::visit([this](const auto &y) { return (*this)(y); }, x.u);
189   }
190   bool operator()(const StructureConstructor &x) {
191     for (const auto &pair : x) {
192       const Expr<SomeType> &y{pair.second.value()};
193       const auto sym{pair.first};
194       const bool compIsConstant{(*this)(y)};
195       // If an allocatable component is initialized by a constant,
196       // the structure constructor is not a constant.
197       if ((!compIsConstant && !IsNullPointer(y)) ||
198           (compIsConstant && IsAllocatable(sym))) {
199         return false;
200       }
201     }
202     return true;
203   }
204   template <typename A> bool operator()(const A *x) { return x && (*this)(*x); }
205   template <typename A> bool operator()(const std::optional<A> &x) {
206     return x && (*this)(*x);
207   }
208 };
209 
210 template <typename A> bool IsActuallyConstant(const A &x) {
211   return IsActuallyConstantHelper{}(x);
212 }
213 
214 template bool IsActuallyConstant(const Expr<SomeType> &);
215 template bool IsActuallyConstant(const Expr<SomeInteger> &);
216 template bool IsActuallyConstant(const Expr<SubscriptInteger> &);
217 template bool IsActuallyConstant(const std::optional<Expr<SubscriptInteger>> &);
218 
219 // Object pointer initialization checking predicate IsInitialDataTarget().
220 // This code determines whether an expression is allowable as the static
221 // data address used to initialize a pointer with "=> x".  See C765.
222 class IsInitialDataTargetHelper
223     : public AllTraverse<IsInitialDataTargetHelper, true> {
224 public:
225   using Base = AllTraverse<IsInitialDataTargetHelper, true>;
226   using Base::operator();
227   explicit IsInitialDataTargetHelper(parser::ContextualMessages *m)
228       : Base{*this}, messages_{m} {}
229 
230   bool emittedMessage() const { return emittedMessage_; }
231 
232   bool operator()(const BOZLiteralConstant &) const { return false; }
233   bool operator()(const NullPointer &) const { return true; }
234   template <typename T> bool operator()(const Constant<T> &) const {
235     return false;
236   }
237   bool operator()(const semantics::Symbol &symbol) {
238     // This function checks only base symbols, not components.
239     const Symbol &ultimate{symbol.GetUltimate()};
240     if (const auto *assoc{
241             ultimate.detailsIf<semantics::AssocEntityDetails>()}) {
242       if (const auto &expr{assoc->expr()}) {
243         if (IsVariable(*expr)) {
244           return (*this)(*expr);
245         } else if (messages_) {
246           messages_->Say(
247               "An initial data target may not be an associated expression ('%s')"_err_en_US,
248               ultimate.name());
249           emittedMessage_ = true;
250         }
251       }
252       return false;
253     } else if (!CheckVarOrComponent(ultimate)) {
254       return false;
255     } else if (!ultimate.attrs().test(semantics::Attr::TARGET)) {
256       if (messages_) {
257         messages_->Say(
258             "An initial data target may not be a reference to an object '%s' that lacks the TARGET attribute"_err_en_US,
259             ultimate.name());
260         emittedMessage_ = true;
261       }
262       return false;
263     } else if (!IsSaved(ultimate)) {
264       if (messages_) {
265         messages_->Say(
266             "An initial data target may not be a reference to an object '%s' that lacks the SAVE attribute"_err_en_US,
267             ultimate.name());
268         emittedMessage_ = true;
269       }
270       return false;
271     } else {
272       return true;
273     }
274   }
275   bool operator()(const StaticDataObject &) const { return false; }
276   bool operator()(const TypeParamInquiry &) const { return false; }
277   bool operator()(const Triplet &x) const {
278     return IsConstantExpr(x.lower()) && IsConstantExpr(x.upper()) &&
279         IsConstantExpr(x.stride());
280   }
281   bool operator()(const Subscript &x) const {
282     return common::visit(common::visitors{
283                              [&](const Triplet &t) { return (*this)(t); },
284                              [&](const auto &y) {
285                                return y.value().Rank() == 0 &&
286                                    IsConstantExpr(y.value());
287                              },
288                          },
289         x.u);
290   }
291   bool operator()(const CoarrayRef &) const { return false; }
292   bool operator()(const Component &x) {
293     return CheckVarOrComponent(x.GetLastSymbol()) && (*this)(x.base());
294   }
295   bool operator()(const Substring &x) const {
296     return IsConstantExpr(x.lower()) && IsConstantExpr(x.upper()) &&
297         (*this)(x.parent());
298   }
299   bool operator()(const DescriptorInquiry &) const { return false; }
300   template <typename T> bool operator()(const ArrayConstructor<T> &) const {
301     return false;
302   }
303   bool operator()(const StructureConstructor &) const { return false; }
304   template <typename D, typename R, typename... O>
305   bool operator()(const Operation<D, R, O...> &) const {
306     return false;
307   }
308   template <typename T> bool operator()(const Parentheses<T> &x) const {
309     return (*this)(x.left());
310   }
311   bool operator()(const ProcedureRef &x) const {
312     if (const SpecificIntrinsic * intrinsic{x.proc().GetSpecificIntrinsic()}) {
313       return intrinsic->characteristics.value().attrs.test(
314           characteristics::Procedure::Attr::NullPointer);
315     }
316     return false;
317   }
318   bool operator()(const Relational<SomeType> &) const { return false; }
319 
320 private:
321   bool CheckVarOrComponent(const semantics::Symbol &symbol) {
322     const Symbol &ultimate{symbol.GetUltimate()};
323     const char *unacceptable{nullptr};
324     if (ultimate.Corank() > 0) {
325       unacceptable = "a coarray";
326     } else if (IsAllocatable(ultimate)) {
327       unacceptable = "an ALLOCATABLE";
328     } else if (IsPointer(ultimate)) {
329       unacceptable = "a POINTER";
330     } else {
331       return true;
332     }
333     if (messages_) {
334       messages_->Say(
335           "An initial data target may not be a reference to %s '%s'"_err_en_US,
336           unacceptable, ultimate.name());
337       emittedMessage_ = true;
338     }
339     return false;
340   }
341 
342   parser::ContextualMessages *messages_;
343   bool emittedMessage_{false};
344 };
345 
346 bool IsInitialDataTarget(
347     const Expr<SomeType> &x, parser::ContextualMessages *messages) {
348   IsInitialDataTargetHelper helper{messages};
349   bool result{helper(x)};
350   if (!result && messages && !helper.emittedMessage()) {
351     messages->Say(
352         "An initial data target must be a designator with constant subscripts"_err_en_US);
353   }
354   return result;
355 }
356 
357 bool IsInitialProcedureTarget(const semantics::Symbol &symbol) {
358   const auto &ultimate{symbol.GetUltimate()};
359   return common::visit(
360       common::visitors{
361           [&](const semantics::SubprogramDetails &subp) {
362             return !subp.isDummy() && !subp.stmtFunction() &&
363                 symbol.owner().kind() != semantics::Scope::Kind::MainProgram &&
364                 symbol.owner().kind() != semantics::Scope::Kind::Subprogram;
365           },
366           [](const semantics::SubprogramNameDetails &x) {
367             return x.kind() != semantics::SubprogramKind::Internal;
368           },
369           [&](const semantics::ProcEntityDetails &proc) {
370             return !semantics::IsPointer(ultimate) && !proc.isDummy();
371           },
372           [](const auto &) { return false; },
373       },
374       ultimate.details());
375 }
376 
377 bool IsInitialProcedureTarget(const ProcedureDesignator &proc) {
378   if (const auto *intrin{proc.GetSpecificIntrinsic()}) {
379     return !intrin->isRestrictedSpecific;
380   } else if (proc.GetComponent()) {
381     return false;
382   } else {
383     return IsInitialProcedureTarget(DEREF(proc.GetSymbol()));
384   }
385 }
386 
387 bool IsInitialProcedureTarget(const Expr<SomeType> &expr) {
388   if (const auto *proc{std::get_if<ProcedureDesignator>(&expr.u)}) {
389     return IsInitialProcedureTarget(*proc);
390   } else {
391     return IsNullProcedurePointer(expr);
392   }
393 }
394 
395 // Converts, folds, and then checks type, rank, and shape of an
396 // initialization expression for a named constant, a non-pointer
397 // variable static initialization, a component default initializer,
398 // a type parameter default value, or instantiated type parameter value.
399 std::optional<Expr<SomeType>> NonPointerInitializationExpr(const Symbol &symbol,
400     Expr<SomeType> &&x, FoldingContext &context,
401     const semantics::Scope *instantiation) {
402   CHECK(!IsPointer(symbol));
403   if (auto symTS{
404           characteristics::TypeAndShape::Characterize(symbol, context)}) {
405     auto xType{x.GetType()};
406     auto converted{ConvertToType(symTS->type(), Expr<SomeType>{x})};
407     if (!converted &&
408         symbol.owner().context().IsEnabled(
409             common::LanguageFeature::LogicalIntegerAssignment)) {
410       converted = DataConstantConversionExtension(context, symTS->type(), x);
411       if (converted &&
412           symbol.owner().context().ShouldWarn(
413               common::LanguageFeature::LogicalIntegerAssignment)) {
414         context.messages().Say(
415             common::LanguageFeature::LogicalIntegerAssignment,
416             "nonstandard usage: initialization of %s with %s"_port_en_US,
417             symTS->type().AsFortran(), x.GetType().value().AsFortran());
418       }
419     }
420     if (converted) {
421       auto folded{Fold(context, std::move(*converted))};
422       if (IsActuallyConstant(folded)) {
423         int symRank{symTS->Rank()};
424         if (IsImpliedShape(symbol)) {
425           if (folded.Rank() == symRank) {
426             return ArrayConstantBoundChanger{
427                 std::move(*AsConstantExtents(
428                     context, GetRawLowerBounds(context, NamedEntity{symbol})))}
429                 .ChangeLbounds(std::move(folded));
430           } else {
431             context.messages().Say(
432                 "Implied-shape parameter '%s' has rank %d but its initializer has rank %d"_err_en_US,
433                 symbol.name(), symRank, folded.Rank());
434           }
435         } else if (auto extents{AsConstantExtents(context, symTS->shape())}) {
436           if (folded.Rank() == 0 && symRank == 0) {
437             // symbol and constant are both scalars
438             return {std::move(folded)};
439           } else if (folded.Rank() == 0 && symRank > 0) {
440             // expand the scalar constant to an array
441             return ScalarConstantExpander{std::move(*extents),
442                 AsConstantExtents(
443                     context, GetRawLowerBounds(context, NamedEntity{symbol}))}
444                 .Expand(std::move(folded));
445           } else if (auto resultShape{GetShape(context, folded)}) {
446             CHECK(symTS->shape()); // Assumed-ranks cannot be initialized.
447             if (CheckConformance(context.messages(), *symTS->shape(),
448                     *resultShape, CheckConformanceFlags::None,
449                     "initialized object", "initialization expression")
450                     .value_or(false /*fail if not known now to conform*/)) {
451               // make a constant array with adjusted lower bounds
452               return ArrayConstantBoundChanger{
453                   std::move(*AsConstantExtents(context,
454                       GetRawLowerBounds(context, NamedEntity{symbol})))}
455                   .ChangeLbounds(std::move(folded));
456             }
457           }
458         } else if (IsNamedConstant(symbol)) {
459           if (IsExplicitShape(symbol)) {
460             context.messages().Say(
461                 "Named constant '%s' array must have constant shape"_err_en_US,
462                 symbol.name());
463           } else {
464             // Declaration checking handles other cases
465           }
466         } else {
467           context.messages().Say(
468               "Shape of initialized object '%s' must be constant"_err_en_US,
469               symbol.name());
470         }
471       } else if (IsErrorExpr(folded)) {
472       } else if (IsLenTypeParameter(symbol)) {
473         return {std::move(folded)};
474       } else if (IsKindTypeParameter(symbol)) {
475         if (instantiation) {
476           context.messages().Say(
477               "Value of kind type parameter '%s' (%s) must be a scalar INTEGER constant"_err_en_US,
478               symbol.name(), folded.AsFortran());
479         } else {
480           return {std::move(folded)};
481         }
482       } else if (IsNamedConstant(symbol)) {
483         if (symbol.name() == "numeric_storage_size" &&
484             symbol.owner().IsModule() &&
485             DEREF(symbol.owner().symbol()).name() == "iso_fortran_env") {
486           // Very special case: numeric_storage_size is not folded until
487           // it read from the iso_fortran_env module file, as its value
488           // depends on compilation options.
489           return {std::move(folded)};
490         }
491         context.messages().Say(
492             "Value of named constant '%s' (%s) cannot be computed as a constant value"_err_en_US,
493             symbol.name(), folded.AsFortran());
494       } else {
495         context.messages().Say(
496             "Initialization expression for '%s' (%s) cannot be computed as a constant value"_err_en_US,
497             symbol.name(), x.AsFortran());
498       }
499     } else if (xType) {
500       context.messages().Say(
501           "Initialization expression cannot be converted to declared type of '%s' from %s"_err_en_US,
502           symbol.name(), xType->AsFortran());
503     } else {
504       context.messages().Say(
505           "Initialization expression cannot be converted to declared type of '%s'"_err_en_US,
506           symbol.name());
507     }
508   }
509   return std::nullopt;
510 }
511 
512 // Specification expression validation (10.1.11(2), C1010)
513 class CheckSpecificationExprHelper
514     : public AnyTraverse<CheckSpecificationExprHelper,
515           std::optional<std::string>> {
516 public:
517   using Result = std::optional<std::string>;
518   using Base = AnyTraverse<CheckSpecificationExprHelper, Result>;
519   explicit CheckSpecificationExprHelper(const semantics::Scope &s,
520       FoldingContext &context, bool forElementalFunctionResult)
521       : Base{*this}, scope_{s}, context_{context},
522         forElementalFunctionResult_{forElementalFunctionResult} {}
523   using Base::operator();
524 
525   Result operator()(const CoarrayRef &) const { return "coindexed reference"; }
526 
527   Result operator()(const semantics::Symbol &symbol) const {
528     const auto &ultimate{symbol.GetUltimate()};
529     const auto *object{ultimate.detailsIf<semantics::ObjectEntityDetails>()};
530     bool isInitialized{semantics::IsSaved(ultimate) &&
531         !IsAllocatable(ultimate) && object &&
532         (ultimate.test(Symbol::Flag::InDataStmt) ||
533             object->init().has_value())};
534     if (const auto *assoc{
535             ultimate.detailsIf<semantics::AssocEntityDetails>()}) {
536       return (*this)(assoc->expr());
537     } else if (semantics::IsNamedConstant(ultimate) ||
538         ultimate.owner().IsModule() || ultimate.owner().IsSubmodule()) {
539       return std::nullopt;
540     } else if (scope_.IsDerivedType() &&
541         IsVariableName(ultimate)) { // C750, C754
542       return "derived type component or type parameter value not allowed to "
543              "reference variable '"s +
544           ultimate.name().ToString() + "'";
545     } else if (IsDummy(ultimate)) {
546       if (!inInquiry_ && forElementalFunctionResult_) {
547         return "dependence on value of dummy argument '"s +
548             ultimate.name().ToString() + "'";
549       } else if (ultimate.attrs().test(semantics::Attr::OPTIONAL)) {
550         return "reference to OPTIONAL dummy argument '"s +
551             ultimate.name().ToString() + "'";
552       } else if (!inInquiry_ &&
553           ultimate.attrs().test(semantics::Attr::INTENT_OUT)) {
554         return "reference to INTENT(OUT) dummy argument '"s +
555             ultimate.name().ToString() + "'";
556       } else if (ultimate.has<semantics::ObjectEntityDetails>()) {
557         return std::nullopt;
558       } else {
559         return "dummy procedure argument";
560       }
561     } else if (&symbol.owner() != &scope_ || &ultimate.owner() != &scope_) {
562       return std::nullopt; // host association is in play
563     } else if (isInitialized &&
564         context_.languageFeatures().IsEnabled(
565             common::LanguageFeature::SavedLocalInSpecExpr)) {
566       if (!scope_.IsModuleFile() &&
567           context_.languageFeatures().ShouldWarn(
568               common::LanguageFeature::SavedLocalInSpecExpr)) {
569         context_.messages().Say(common::LanguageFeature::SavedLocalInSpecExpr,
570             "specification expression refers to local object '%s' (initialized and saved)"_port_en_US,
571             ultimate.name().ToString());
572       }
573       return std::nullopt;
574     } else if (const auto *object{
575                    ultimate.detailsIf<semantics::ObjectEntityDetails>()}) {
576       if (object->commonBlock()) {
577         return std::nullopt;
578       }
579     }
580     if (inInquiry_) {
581       return std::nullopt;
582     } else {
583       return "reference to local entity '"s + ultimate.name().ToString() + "'";
584     }
585   }
586 
587   Result operator()(const Component &x) const {
588     // Don't look at the component symbol.
589     return (*this)(x.base());
590   }
591   Result operator()(const ArrayRef &x) const {
592     if (auto result{(*this)(x.base())}) {
593       return result;
594     }
595     // The subscripts don't get special protection for being in a
596     // specification inquiry context;
597     auto restorer{common::ScopedSet(inInquiry_, false)};
598     return (*this)(x.subscript());
599   }
600   Result operator()(const Substring &x) const {
601     if (auto result{(*this)(x.parent())}) {
602       return result;
603     }
604     // The bounds don't get special protection for being in a
605     // specification inquiry context;
606     auto restorer{common::ScopedSet(inInquiry_, false)};
607     if (auto result{(*this)(x.lower())}) {
608       return result;
609     }
610     return (*this)(x.upper());
611   }
612   Result operator()(const DescriptorInquiry &x) const {
613     // Many uses of SIZE(), LBOUND(), &c. that are valid in specification
614     // expressions will have been converted to expressions over descriptor
615     // inquiries by Fold().
616     // Catch REAL, ALLOCATABLE :: X(:); REAL :: Y(SIZE(X))
617     if (IsPermissibleInquiry(
618             x.base().GetFirstSymbol(), x.base().GetLastSymbol(), x.field())) {
619       auto restorer{common::ScopedSet(inInquiry_, true)};
620       return (*this)(x.base());
621     } else if (IsConstantExpr(x)) {
622       return std::nullopt;
623     } else {
624       return "non-constant descriptor inquiry not allowed for local object";
625     }
626   }
627 
628   Result operator()(const TypeParamInquiry &inq) const {
629     if (scope_.IsDerivedType()) {
630       if (!IsConstantExpr(inq) &&
631           inq.base() /* X%T, not local T */) { // C750, C754
632         return "non-constant reference to a type parameter inquiry not allowed "
633                "for derived type components or type parameter values";
634       }
635     } else if (inq.base() &&
636         IsInquiryAlwaysPermissible(inq.base()->GetFirstSymbol())) {
637       auto restorer{common::ScopedSet(inInquiry_, true)};
638       return (*this)(inq.base());
639     } else if (!IsConstantExpr(inq)) {
640       return "non-constant type parameter inquiry not allowed for local object";
641     }
642     return std::nullopt;
643   }
644 
645   Result operator()(const ProcedureRef &x) const {
646     bool inInquiry{false};
647     if (const auto *symbol{x.proc().GetSymbol()}) {
648       const Symbol &ultimate{symbol->GetUltimate()};
649       if (!semantics::IsPureProcedure(ultimate)) {
650         return "reference to impure function '"s + ultimate.name().ToString() +
651             "'";
652       }
653       if (semantics::IsStmtFunction(ultimate)) {
654         return "reference to statement function '"s +
655             ultimate.name().ToString() + "'";
656       }
657       if (scope_.IsDerivedType()) { // C750, C754
658         return "reference to function '"s + ultimate.name().ToString() +
659             "' not allowed for derived type components or type parameter"
660             " values";
661       }
662       if (auto procChars{characteristics::Procedure::Characterize(
663               x.proc(), context_, /*emitError=*/true)}) {
664         const auto iter{std::find_if(procChars->dummyArguments.begin(),
665             procChars->dummyArguments.end(),
666             [](const characteristics::DummyArgument &dummy) {
667               return std::holds_alternative<characteristics::DummyProcedure>(
668                   dummy.u);
669             })};
670         if (iter != procChars->dummyArguments.end() &&
671             ultimate.name().ToString() != "__builtin_c_funloc") {
672           return "reference to function '"s + ultimate.name().ToString() +
673               "' with dummy procedure argument '" + iter->name + '\'';
674         }
675       }
676       // References to internal functions are caught in expression semantics.
677       // TODO: other checks for standard module procedures
678     } else { // intrinsic
679       const SpecificIntrinsic &intrin{DEREF(x.proc().GetSpecificIntrinsic())};
680       inInquiry = context_.intrinsics().GetIntrinsicClass(intrin.name) ==
681           IntrinsicClass::inquiryFunction;
682       if (scope_.IsDerivedType()) { // C750, C754
683         if ((context_.intrinsics().IsIntrinsic(intrin.name) &&
684                 badIntrinsicsForComponents_.find(intrin.name) !=
685                     badIntrinsicsForComponents_.end())) {
686           return "reference to intrinsic '"s + intrin.name +
687               "' not allowed for derived type components or type parameter"
688               " values";
689         }
690         if (inInquiry && !IsConstantExpr(x)) {
691           return "non-constant reference to inquiry intrinsic '"s +
692               intrin.name +
693               "' not allowed for derived type components or type"
694               " parameter values";
695         }
696       }
697       // Type-determined inquiries (DIGITS, HUGE, &c.) will have already been
698       // folded and won't arrive here.  Inquiries that are represented with
699       // DescriptorInquiry operations (LBOUND) are checked elsewhere.  If a
700       // call that makes it to here satisfies the requirements of a constant
701       // expression (as Fortran defines it), it's fine.
702       if (IsConstantExpr(x)) {
703         return std::nullopt;
704       }
705       if (intrin.name == "present") {
706         return std::nullopt; // always ok
707       }
708       // Catch CHARACTER(:), ALLOCATABLE :: X; CHARACTER(LEN(X)) :: Y
709       if (inInquiry && x.arguments().size() >= 1) {
710         if (const auto &arg{x.arguments().at(0)}) {
711           if (auto dataRef{ExtractDataRef(*arg, true, true)}) {
712             if (intrin.name == "allocated" || intrin.name == "associated" ||
713                 intrin.name == "is_contiguous") { // ok
714             } else if (intrin.name == "len" &&
715                 IsPermissibleInquiry(dataRef->GetFirstSymbol(),
716                     dataRef->GetLastSymbol(),
717                     DescriptorInquiry::Field::Len)) { // ok
718             } else if (intrin.name == "lbound" &&
719                 IsPermissibleInquiry(dataRef->GetFirstSymbol(),
720                     dataRef->GetLastSymbol(),
721                     DescriptorInquiry::Field::LowerBound)) { // ok
722             } else if ((intrin.name == "shape" || intrin.name == "size" ||
723                            intrin.name == "sizeof" ||
724                            intrin.name == "storage_size" ||
725                            intrin.name == "ubound") &&
726                 IsPermissibleInquiry(dataRef->GetFirstSymbol(),
727                     dataRef->GetLastSymbol(),
728                     DescriptorInquiry::Field::Extent)) { // ok
729             } else {
730               return "non-constant inquiry function '"s + intrin.name +
731                   "' not allowed for local object";
732             }
733           }
734         }
735       }
736     }
737     auto restorer{common::ScopedSet(inInquiry_, inInquiry)};
738     return (*this)(x.arguments());
739   }
740 
741 private:
742   const semantics::Scope &scope_;
743   FoldingContext &context_;
744   // Contextual information: this flag is true when in an argument to
745   // an inquiry intrinsic like SIZE().
746   mutable bool inInquiry_{false};
747   bool forElementalFunctionResult_{false}; // F'2023 C15121
748   const std::set<std::string> badIntrinsicsForComponents_{
749       "allocated", "associated", "extends_type_of", "present", "same_type_as"};
750 
751   bool IsInquiryAlwaysPermissible(const semantics::Symbol &) const;
752   bool IsPermissibleInquiry(const semantics::Symbol &firstSymbol,
753       const semantics::Symbol &lastSymbol,
754       DescriptorInquiry::Field field) const;
755 };
756 
757 bool CheckSpecificationExprHelper::IsInquiryAlwaysPermissible(
758     const semantics::Symbol &symbol) const {
759   if (&symbol.owner() != &scope_ || symbol.has<semantics::UseDetails>() ||
760       symbol.owner().kind() == semantics::Scope::Kind::Module ||
761       semantics::FindCommonBlockContaining(symbol) ||
762       symbol.has<semantics::HostAssocDetails>()) {
763     return true; // it's nonlocal
764   } else if (semantics::IsDummy(symbol) && !forElementalFunctionResult_) {
765     return true;
766   } else {
767     return false;
768   }
769 }
770 
771 bool CheckSpecificationExprHelper::IsPermissibleInquiry(
772     const semantics::Symbol &firstSymbol, const semantics::Symbol &lastSymbol,
773     DescriptorInquiry::Field field) const {
774   if (IsInquiryAlwaysPermissible(firstSymbol)) {
775     return true;
776   }
777   // Inquiries on local objects may not access a deferred bound or length.
778   // (This code used to be a switch, but it proved impossible to write it
779   // thus without running afoul of bogus warnings from different C++
780   // compilers.)
781   if (field == DescriptorInquiry::Field::Rank) {
782     return true; // always known
783   }
784   const auto *object{lastSymbol.detailsIf<semantics::ObjectEntityDetails>()};
785   if (field == DescriptorInquiry::Field::LowerBound ||
786       field == DescriptorInquiry::Field::Extent ||
787       field == DescriptorInquiry::Field::Stride) {
788     return object && !object->shape().CanBeDeferredShape();
789   }
790   if (field == DescriptorInquiry::Field::Len) {
791     return object && object->type() &&
792         object->type()->category() == semantics::DeclTypeSpec::Character &&
793         !object->type()->characterTypeSpec().length().isDeferred();
794   }
795   return false;
796 }
797 
798 template <typename A>
799 void CheckSpecificationExpr(const A &x, const semantics::Scope &scope,
800     FoldingContext &context, bool forElementalFunctionResult) {
801   CheckSpecificationExprHelper helper{
802       scope, context, forElementalFunctionResult};
803   if (auto why{helper(x)}) {
804     context.messages().Say("Invalid specification expression%s: %s"_err_en_US,
805         forElementalFunctionResult ? " for elemental function result" : "",
806         *why);
807   }
808 }
809 
810 template void CheckSpecificationExpr(const Expr<SomeType> &,
811     const semantics::Scope &, FoldingContext &,
812     bool forElementalFunctionResult);
813 template void CheckSpecificationExpr(const Expr<SomeInteger> &,
814     const semantics::Scope &, FoldingContext &,
815     bool forElementalFunctionResult);
816 template void CheckSpecificationExpr(const Expr<SubscriptInteger> &,
817     const semantics::Scope &, FoldingContext &,
818     bool forElementalFunctionResult);
819 template void CheckSpecificationExpr(const std::optional<Expr<SomeType>> &,
820     const semantics::Scope &, FoldingContext &,
821     bool forElementalFunctionResult);
822 template void CheckSpecificationExpr(const std::optional<Expr<SomeInteger>> &,
823     const semantics::Scope &, FoldingContext &,
824     bool forElementalFunctionResult);
825 template void CheckSpecificationExpr(
826     const std::optional<Expr<SubscriptInteger>> &, const semantics::Scope &,
827     FoldingContext &, bool forElementalFunctionResult);
828 
829 // IsContiguous() -- 9.5.4
830 class IsContiguousHelper
831     : public AnyTraverse<IsContiguousHelper, std::optional<bool>> {
832 public:
833   using Result = std::optional<bool>; // tri-state
834   using Base = AnyTraverse<IsContiguousHelper, Result>;
835   explicit IsContiguousHelper(FoldingContext &c) : Base{*this}, context_{c} {}
836   using Base::operator();
837 
838   template <typename T> Result operator()(const Constant<T> &) const {
839     return true;
840   }
841   Result operator()(const StaticDataObject &) const { return true; }
842   Result operator()(const semantics::Symbol &symbol) const {
843     const auto &ultimate{symbol.GetUltimate()};
844     if (ultimate.attrs().test(semantics::Attr::CONTIGUOUS)) {
845       return true;
846     } else if (!IsVariable(symbol)) {
847       return true;
848     } else if (ultimate.Rank() == 0) {
849       // Extension: accept scalars as a degenerate case of
850       // simple contiguity to allow their use in contexts like
851       // data targets in pointer assignments with remapping.
852       return true;
853     } else if (const auto *details{
854                    ultimate.detailsIf<semantics::AssocEntityDetails>()}) {
855       // RANK(*) associating entity is contiguous.
856       if (details->IsAssumedSize()) {
857         return true;
858       } else {
859         return Base::operator()(ultimate); // use expr
860       }
861     } else if (semantics::IsPointer(ultimate) ||
862         semantics::IsAssumedShape(ultimate) || IsAssumedRank(ultimate)) {
863       return std::nullopt;
864     } else if (ultimate.has<semantics::ObjectEntityDetails>()) {
865       return true;
866     } else {
867       return Base::operator()(ultimate);
868     }
869   }
870 
871   Result operator()(const ArrayRef &x) const {
872     if (x.Rank() == 0) {
873       return true; // scalars considered contiguous
874     }
875     int subscriptRank{0};
876     auto baseLbounds{GetLBOUNDs(context_, x.base())};
877     auto baseUbounds{GetUBOUNDs(context_, x.base())};
878     auto subscripts{CheckSubscripts(
879         x.subscript(), subscriptRank, &baseLbounds, &baseUbounds)};
880     if (!subscripts.value_or(false)) {
881       return subscripts; // subscripts not known to be contiguous
882     } else if (subscriptRank > 0) {
883       // a(1)%b(:,:) is contiguous if and only if a(1)%b is contiguous.
884       return (*this)(x.base());
885     } else {
886       // a(:)%b(1,1) is (probably) not contiguous.
887       return std::nullopt;
888     }
889   }
890   Result operator()(const CoarrayRef &x) const {
891     int rank{0};
892     return CheckSubscripts(x.subscript(), rank).has_value();
893   }
894   Result operator()(const Component &x) const {
895     if (x.base().Rank() == 0) {
896       return (*this)(x.GetLastSymbol());
897     } else {
898       if (Result baseIsContiguous{(*this)(x.base())}) {
899         if (!*baseIsContiguous) {
900           return false;
901         }
902         // TODO could be true if base contiguous and this is only component, or
903         // if base has only one element?
904       }
905       return std::nullopt;
906     }
907   }
908   Result operator()(const ComplexPart &x) const {
909     return x.complex().Rank() == 0;
910   }
911   Result operator()(const Substring &) const { return std::nullopt; }
912 
913   Result operator()(const ProcedureRef &x) const {
914     if (auto chars{characteristics::Procedure::Characterize(
915             x.proc(), context_, /*emitError=*/true)}) {
916       if (chars->functionResult) {
917         const auto &result{*chars->functionResult};
918         if (!result.IsProcedurePointer()) {
919           if (result.attrs.test(
920                   characteristics::FunctionResult::Attr::Contiguous)) {
921             return true;
922           }
923           if (!result.attrs.test(
924                   characteristics::FunctionResult::Attr::Pointer)) {
925             return true;
926           }
927           if (const auto *type{result.GetTypeAndShape()};
928               type && type->Rank() == 0) {
929             return true; // pointer to scalar
930           }
931           // Must be non-CONTIGUOUS pointer to array
932         }
933       }
934     }
935     return std::nullopt;
936   }
937 
938   Result operator()(const NullPointer &) const { return true; }
939 
940 private:
941   // Returns "true" for a provably empty or simply contiguous array section;
942   // return "false" for a provably nonempty discontiguous section or for use
943   // of a vector subscript.
944   std::optional<bool> CheckSubscripts(const std::vector<Subscript> &subscript,
945       int &rank, const Shape *baseLbounds = nullptr,
946       const Shape *baseUbounds = nullptr) const {
947     bool anyTriplet{false};
948     rank = 0;
949     // Detect any provably empty dimension in this array section, which would
950     // render the whole section empty and therefore vacuously contiguous.
951     std::optional<bool> result;
952     bool mayBeEmpty{false};
953     auto dims{subscript.size()};
954     std::vector<bool> knownPartialSlice(dims, false);
955     for (auto j{dims}; j-- > 0;) {
956       std::optional<ConstantSubscript> dimLbound;
957       std::optional<ConstantSubscript> dimUbound;
958       std::optional<ConstantSubscript> dimExtent;
959       if (baseLbounds && j < baseLbounds->size()) {
960         if (const auto &lb{baseLbounds->at(j)}) {
961           dimLbound = ToInt64(Fold(context_, Expr<SubscriptInteger>{*lb}));
962         }
963       }
964       if (baseUbounds && j < baseUbounds->size()) {
965         if (const auto &ub{baseUbounds->at(j)}) {
966           dimUbound = ToInt64(Fold(context_, Expr<SubscriptInteger>{*ub}));
967         }
968       }
969       if (dimLbound && dimUbound) {
970         if (*dimLbound <= *dimUbound) {
971           dimExtent = *dimUbound - *dimLbound + 1;
972         } else {
973           // This is an empty dimension.
974           result = true;
975           dimExtent = 0;
976         }
977       }
978 
979       if (const auto *triplet{std::get_if<Triplet>(&subscript[j].u)}) {
980         ++rank;
981         if (auto stride{ToInt64(triplet->stride())}) {
982           const Expr<SubscriptInteger> *lowerBound{triplet->GetLower()};
983           const Expr<SubscriptInteger> *upperBound{triplet->GetUpper()};
984           std::optional<ConstantSubscript> lowerVal{lowerBound
985                   ? ToInt64(Fold(context_, Expr<SubscriptInteger>{*lowerBound}))
986                   : dimLbound};
987           std::optional<ConstantSubscript> upperVal{upperBound
988                   ? ToInt64(Fold(context_, Expr<SubscriptInteger>{*upperBound}))
989                   : dimUbound};
990           if (lowerVal && upperVal) {
991             if (*lowerVal < *upperVal) {
992               if (*stride < 0) {
993                 result = true; // empty dimension
994               } else if (!result && *stride > 1 &&
995                   *lowerVal + *stride <= *upperVal) {
996                 result = false; // discontiguous if not empty
997               }
998             } else if (*lowerVal > *upperVal) {
999               if (*stride > 0) {
1000                 result = true; // empty dimension
1001               } else if (!result && *stride < 0 &&
1002                   *lowerVal + *stride >= *upperVal) {
1003                 result = false; // discontiguous if not empty
1004               }
1005             } else {
1006               mayBeEmpty = true;
1007             }
1008           } else {
1009             mayBeEmpty = true;
1010           }
1011         } else {
1012           mayBeEmpty = true;
1013         }
1014       } else if (subscript[j].Rank() > 0) {
1015         ++rank;
1016         if (!result) {
1017           result = false; // vector subscript
1018         }
1019         mayBeEmpty = true;
1020       } else {
1021         // Scalar subscript.
1022         if (dimExtent && *dimExtent > 1) {
1023           knownPartialSlice[j] = true;
1024         }
1025       }
1026     }
1027     if (rank == 0) {
1028       result = true; // scalar
1029     }
1030     if (result) {
1031       return result;
1032     }
1033     // Not provably discontiguous at this point.
1034     // Return "true" if simply contiguous, otherwise nullopt.
1035     for (auto j{subscript.size()}; j-- > 0;) {
1036       if (const auto *triplet{std::get_if<Triplet>(&subscript[j].u)}) {
1037         auto stride{ToInt64(triplet->stride())};
1038         if (!stride || stride != 1) {
1039           return std::nullopt;
1040         } else if (anyTriplet) {
1041           if (triplet->GetLower() || triplet->GetUpper()) {
1042             // all triplets before the last one must be just ":" for
1043             // simple contiguity
1044             return std::nullopt;
1045           }
1046         } else {
1047           anyTriplet = true;
1048         }
1049         ++rank;
1050       } else if (anyTriplet) {
1051         // If the section cannot be empty, and this dimension's
1052         // scalar subscript is known not to cover the whole
1053         // dimension, then the array section is provably
1054         // discontiguous.
1055         return (mayBeEmpty || !knownPartialSlice[j])
1056             ? std::nullopt
1057             : std::make_optional(false);
1058       }
1059     }
1060     return true; // simply contiguous
1061   }
1062 
1063   FoldingContext &context_;
1064 };
1065 
1066 template <typename A>
1067 std::optional<bool> IsContiguous(const A &x, FoldingContext &context) {
1068   return IsContiguousHelper{context}(x);
1069 }
1070 
1071 template std::optional<bool> IsContiguous(
1072     const Expr<SomeType> &, FoldingContext &);
1073 template std::optional<bool> IsContiguous(const ArrayRef &, FoldingContext &);
1074 template std::optional<bool> IsContiguous(const Substring &, FoldingContext &);
1075 template std::optional<bool> IsContiguous(const Component &, FoldingContext &);
1076 template std::optional<bool> IsContiguous(
1077     const ComplexPart &, FoldingContext &);
1078 template std::optional<bool> IsContiguous(const CoarrayRef &, FoldingContext &);
1079 template std::optional<bool> IsContiguous(const Symbol &, FoldingContext &);
1080 
1081 // IsErrorExpr()
1082 struct IsErrorExprHelper : public AnyTraverse<IsErrorExprHelper, bool> {
1083   using Result = bool;
1084   using Base = AnyTraverse<IsErrorExprHelper, Result>;
1085   IsErrorExprHelper() : Base{*this} {}
1086   using Base::operator();
1087 
1088   bool operator()(const SpecificIntrinsic &x) {
1089     return x.name == IntrinsicProcTable::InvalidName;
1090   }
1091 };
1092 
1093 template <typename A> bool IsErrorExpr(const A &x) {
1094   return IsErrorExprHelper{}(x);
1095 }
1096 
1097 template bool IsErrorExpr(const Expr<SomeType> &);
1098 
1099 // C1577
1100 // TODO: Also check C1579 & C1582 here
1101 class StmtFunctionChecker
1102     : public AnyTraverse<StmtFunctionChecker, std::optional<parser::Message>> {
1103 public:
1104   using Result = std::optional<parser::Message>;
1105   using Base = AnyTraverse<StmtFunctionChecker, Result>;
1106 
1107   static constexpr auto feature{
1108       common::LanguageFeature::StatementFunctionExtensions};
1109 
1110   StmtFunctionChecker(const Symbol &sf, FoldingContext &context)
1111       : Base{*this}, sf_{sf}, context_{context} {
1112     if (!context_.languageFeatures().IsEnabled(feature)) {
1113       severity_ = parser::Severity::Error;
1114     } else if (context_.languageFeatures().ShouldWarn(feature)) {
1115       severity_ = parser::Severity::Portability;
1116     }
1117   }
1118   using Base::operator();
1119 
1120   Result Return(parser::Message &&msg) const {
1121     if (severity_) {
1122       msg.set_severity(*severity_);
1123       if (*severity_ != parser::Severity::Error) {
1124         msg.set_languageFeature(feature);
1125       }
1126     }
1127     return std::move(msg);
1128   }
1129 
1130   template <typename T> Result operator()(const ArrayConstructor<T> &) const {
1131     if (severity_) {
1132       return Return(parser::Message{sf_.name(),
1133           "Statement function '%s' should not contain an array constructor"_port_en_US,
1134           sf_.name()});
1135     } else {
1136       return std::nullopt;
1137     }
1138   }
1139   Result operator()(const StructureConstructor &) const {
1140     if (severity_) {
1141       return Return(parser::Message{sf_.name(),
1142           "Statement function '%s' should not contain a structure constructor"_port_en_US,
1143           sf_.name()});
1144     } else {
1145       return std::nullopt;
1146     }
1147   }
1148   Result operator()(const TypeParamInquiry &) const {
1149     if (severity_) {
1150       return Return(parser::Message{sf_.name(),
1151           "Statement function '%s' should not contain a type parameter inquiry"_port_en_US,
1152           sf_.name()});
1153     } else {
1154       return std::nullopt;
1155     }
1156   }
1157   Result operator()(const ProcedureDesignator &proc) const {
1158     if (const Symbol * symbol{proc.GetSymbol()}) {
1159       const Symbol &ultimate{symbol->GetUltimate()};
1160       if (const auto *subp{
1161               ultimate.detailsIf<semantics::SubprogramDetails>()}) {
1162         if (subp->stmtFunction() && &ultimate.owner() == &sf_.owner()) {
1163           if (ultimate.name().begin() > sf_.name().begin()) {
1164             return parser::Message{sf_.name(),
1165                 "Statement function '%s' may not reference another statement function '%s' that is defined later"_err_en_US,
1166                 sf_.name(), ultimate.name()};
1167           }
1168         }
1169       }
1170       if (auto chars{characteristics::Procedure::Characterize(
1171               proc, context_, /*emitError=*/true)}) {
1172         if (!chars->CanBeCalledViaImplicitInterface()) {
1173           if (severity_) {
1174             return Return(parser::Message{sf_.name(),
1175                 "Statement function '%s' should not reference function '%s' that requires an explicit interface"_port_en_US,
1176                 sf_.name(), symbol->name()});
1177           }
1178         }
1179       }
1180     }
1181     if (proc.Rank() > 0) {
1182       if (severity_) {
1183         return Return(parser::Message{sf_.name(),
1184             "Statement function '%s' should not reference a function that returns an array"_port_en_US,
1185             sf_.name()});
1186       }
1187     }
1188     return std::nullopt;
1189   }
1190   Result operator()(const ActualArgument &arg) const {
1191     if (const auto *expr{arg.UnwrapExpr()}) {
1192       if (auto result{(*this)(*expr)}) {
1193         return result;
1194       }
1195       if (expr->Rank() > 0 && !UnwrapWholeSymbolOrComponentDataRef(*expr)) {
1196         if (severity_) {
1197           return Return(parser::Message{sf_.name(),
1198               "Statement function '%s' should not pass an array argument that is not a whole array"_port_en_US,
1199               sf_.name()});
1200         }
1201       }
1202     }
1203     return std::nullopt;
1204   }
1205 
1206 private:
1207   const Symbol &sf_;
1208   FoldingContext &context_;
1209   std::optional<parser::Severity> severity_;
1210 };
1211 
1212 std::optional<parser::Message> CheckStatementFunction(
1213     const Symbol &sf, const Expr<SomeType> &expr, FoldingContext &context) {
1214   return StmtFunctionChecker{sf, context}(expr);
1215 }
1216 
1217 } // namespace Fortran::evaluate
1218