xref: /openbsd-src/gnu/usr.bin/perl/lib/warnings.pm (revision ff0e7be1ebbcc809ea8ad2b6dafe215824da9e46) 
1# -*- buffer-read-only: t -*-
2# !!!!!!!   DO NOT EDIT THIS FILE   !!!!!!!
3# This file is built by regen/warnings.pl.
4# Any changes made here will be lost!
5
6package warnings;
7
8our $VERSION = "1.58";
9
10# Verify that we're called correctly so that warnings will work.
11# Can't use Carp, since Carp uses us!
12# String regexps because constant folding = smaller optree = less memory vs regexp literal
13# see also strict.pm.
14die sprintf "Incorrect use of pragma '%s' at %s line %d.\n", __PACKAGE__, +(caller)[1,2]
15    if __FILE__ !~ ( '(?x) \b     '.__PACKAGE__.'  \.pmc? \z' )
16    && __FILE__ =~ ( '(?x) \b (?i:'.__PACKAGE__.') \.pmc? \z' );
17
18our %Offsets = (
19    # Warnings Categories added in Perl 5.008
20    'all'				=> 0,
21    'closure'				=> 2,
22    'deprecated'			=> 4,
23    'exiting'				=> 6,
24    'glob'				=> 8,
25    'io'				=> 10,
26    'closed'				=> 12,
27    'exec'				=> 14,
28    'layer'				=> 16,
29    'newline'				=> 18,
30    'pipe'				=> 20,
31    'unopened'				=> 22,
32    'misc'				=> 24,
33    'numeric'				=> 26,
34    'once'				=> 28,
35    'overflow'				=> 30,
36    'pack'				=> 32,
37    'portable'				=> 34,
38    'recursion'				=> 36,
39    'redefine'				=> 38,
40    'regexp'				=> 40,
41    'severe'				=> 42,
42    'debugging'				=> 44,
43    'inplace'				=> 46,
44    'internal'				=> 48,
45    'malloc'				=> 50,
46    'signal'				=> 52,
47    'substr'				=> 54,
48    'syntax'				=> 56,
49    'ambiguous'				=> 58,
50    'bareword'				=> 60,
51    'digit'				=> 62,
52    'parenthesis'			=> 64,
53    'precedence'			=> 66,
54    'printf'				=> 68,
55    'prototype'				=> 70,
56    'qw'				=> 72,
57    'reserved'				=> 74,
58    'semicolon'				=> 76,
59    'taint'				=> 78,
60    'threads'				=> 80,
61    'uninitialized'			=> 82,
62    'unpack'				=> 84,
63    'untie'				=> 86,
64    'utf8'				=> 88,
65    'void'				=> 90,
66
67    # Warnings Categories added in Perl 5.011
68    'imprecision'			=> 92,
69    'illegalproto'			=> 94,
70
71    # Warnings Categories added in Perl 5.013
72    'non_unicode'			=> 96,
73    'nonchar'				=> 98,
74    'surrogate'				=> 100,
75
76    # Warnings Categories added in Perl 5.017
77    'experimental'			=> 102,
78    'experimental::lexical_subs'	=> 104,
79    'experimental::regex_sets'		=> 106,
80    'experimental::smartmatch'		=> 108,
81
82    # Warnings Categories added in Perl 5.019
83    'experimental::postderef'		=> 110,
84    'experimental::signatures'		=> 112,
85    'syscalls'				=> 114,
86
87    # Warnings Categories added in Perl 5.021
88    'experimental::bitwise'		=> 116,
89    'experimental::const_attr'		=> 118,
90    'experimental::re_strict'		=> 120,
91    'experimental::refaliasing'		=> 122,
92    'locale'				=> 124,
93    'missing'				=> 126,
94    'redundant'				=> 128,
95
96    # Warnings Categories added in Perl 5.025
97    'experimental::declared_refs'	=> 130,
98
99    # Warnings Categories added in Perl 5.027
100    'experimental::alpha_assertions'	=> 132,
101    'experimental::script_run'		=> 134,
102    'shadow'				=> 136,
103
104    # Warnings Categories added in Perl 5.029
105    'experimental::private_use'		=> 138,
106    'experimental::uniprop_wildcards'	=> 140,
107    'experimental::vlb'			=> 142,
108
109    # Warnings Categories added in Perl 5.031
110    'experimental::isa'			=> 144,
111
112    # Warnings Categories added in Perl 5.033
113    'experimental::try'			=> 146,
114
115    # Warnings Categories added in Perl 5.035
116    'experimental::args_array_with_signatures'=> 148,
117    'experimental::builtin'		=> 150,
118    'experimental::defer'		=> 152,
119    'experimental::extra_paired_delimiters'=> 154,
120    'experimental::for_list'		=> 156,
121    'scalar'				=> 158,
122);
123
124our %Bits = (
125    'all'				=> "\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55\x55", # [0..79]
126    'ambiguous'				=> "\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [29]
127    'bareword'				=> "\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [30]
128    'closed'				=> "\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [6]
129    'closure'				=> "\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [1]
130    'debugging'				=> "\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [22]
131    'deprecated'			=> "\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [2]
132    'digit'				=> "\x00\x00\x00\x00\x00\x00\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [31]
133    'exec'				=> "\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [7]
134    'exiting'				=> "\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [3]
135    'experimental'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40\x55\x51\x05\x54\x54\x55\x15", # [51..56,58..61,65..67,69..78]
136    'experimental::alpha_assertions'	=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00", # [66]
137    'experimental::args_array_with_signatures'=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00", # [74]
138    'experimental::bitwise'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00", # [58]
139    'experimental::builtin'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40\x00", # [75]
140    'experimental::const_attr'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40\x00\x00\x00\x00\x00", # [59]
141    'experimental::declared_refs'	=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00", # [65]
142    'experimental::defer'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01", # [76]
143    'experimental::extra_paired_delimiters'=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04", # [77]
144    'experimental::for_list'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10", # [78]
145    'experimental::isa'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00", # [72]
146    'experimental::lexical_subs'	=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00", # [52]
147    'experimental::postderef'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40\x00\x00\x00\x00\x00\x00", # [55]
148    'experimental::private_use'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00", # [69]
149    'experimental::re_strict'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00", # [60]
150    'experimental::refaliasing'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00", # [61]
151    'experimental::regex_sets'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00", # [53]
152    'experimental::script_run'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40\x00\x00\x00", # [67]
153    'experimental::signatures'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00", # [56]
154    'experimental::smartmatch'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00", # [54]
155    'experimental::try'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00", # [73]
156    'experimental::uniprop_wildcards'	=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00", # [70]
157    'experimental::vlb'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40\x00\x00", # [71]
158    'glob'				=> "\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [4]
159    'illegalproto'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00", # [47]
160    'imprecision'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00", # [46]
161    'inplace'				=> "\x00\x00\x00\x00\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [23]
162    'internal'				=> "\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [24]
163    'io'				=> "\x00\x54\x55\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00", # [5..11,57]
164    'layer'				=> "\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [8]
165    'locale'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00", # [62]
166    'malloc'				=> "\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [25]
167    'misc'				=> "\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [12]
168    'missing'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40\x00\x00\x00\x00", # [63]
169    'newline'				=> "\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [9]
170    'non_unicode'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00", # [48]
171    'nonchar'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00", # [49]
172    'numeric'				=> "\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [13]
173    'once'				=> "\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [14]
174    'overflow'				=> "\x00\x00\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [15]
175    'pack'				=> "\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [16]
176    'parenthesis'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [32]
177    'pipe'				=> "\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [10]
178    'portable'				=> "\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [17]
179    'precedence'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [33]
180    'printf'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [34]
181    'prototype'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [35]
182    'qw'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [36]
183    'recursion'				=> "\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [18]
184    'redefine'				=> "\x00\x00\x00\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [19]
185    'redundant'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00", # [64]
186    'regexp'				=> "\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [20]
187    'reserved'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [37]
188    'scalar'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40", # [79]
189    'semicolon'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [38]
190    'severe'				=> "\x00\x00\x00\x00\x00\x54\x05\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [21..25]
191    'shadow'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00", # [68]
192    'signal'				=> "\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [26]
193    'substr'				=> "\x00\x00\x00\x00\x00\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [27]
194    'surrogate'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00", # [50]
195    'syntax'				=> "\x00\x00\x00\x00\x00\x00\x00\x55\x55\x15\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00", # [28..38,47]
196    'syscalls'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00", # [57]
197    'taint'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [39]
198    'threads'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [40]
199    'uninitialized'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [41]
200    'unopened'				=> "\x00\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [11]
201    'unpack'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [42]
202    'untie'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x40\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [43]
203    'utf8'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x15\x00\x00\x00\x00\x00\x00\x00", # [44,48..50]
204    'void'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00", # [45]
205);
206
207our %DeadBits = (
208    'all'				=> "\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa", # [0..79]
209    'ambiguous'				=> "\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [29]
210    'bareword'				=> "\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [30]
211    'closed'				=> "\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [6]
212    'closure'				=> "\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [1]
213    'debugging'				=> "\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [22]
214    'deprecated'			=> "\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [2]
215    'digit'				=> "\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [31]
216    'exec'				=> "\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [7]
217    'exiting'				=> "\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [3]
218    'experimental'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\xaa\xa2\x0a\xa8\xa8\xaa\x2a", # [51..56,58..61,65..67,69..78]
219    'experimental::alpha_assertions'	=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00", # [66]
220    'experimental::args_array_with_signatures'=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00", # [74]
221    'experimental::bitwise'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00", # [58]
222    'experimental::builtin'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00", # [75]
223    'experimental::const_attr'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00\x00\x00", # [59]
224    'experimental::declared_refs'	=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00", # [65]
225    'experimental::defer'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02", # [76]
226    'experimental::extra_paired_delimiters'=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08", # [77]
227    'experimental::for_list'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20", # [78]
228    'experimental::isa'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00", # [72]
229    'experimental::lexical_subs'	=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00", # [52]
230    'experimental::postderef'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00", # [55]
231    'experimental::private_use'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00", # [69]
232    'experimental::re_strict'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00", # [60]
233    'experimental::refaliasing'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00", # [61]
234    'experimental::regex_sets'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00", # [53]
235    'experimental::script_run'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00", # [67]
236    'experimental::signatures'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00", # [56]
237    'experimental::smartmatch'		=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00", # [54]
238    'experimental::try'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00", # [73]
239    'experimental::uniprop_wildcards'	=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00", # [70]
240    'experimental::vlb'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00", # [71]
241    'glob'				=> "\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [4]
242    'illegalproto'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00", # [47]
243    'imprecision'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00", # [46]
244    'inplace'				=> "\x00\x00\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [23]
245    'internal'				=> "\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [24]
246    'io'				=> "\x00\xa8\xaa\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00", # [5..11,57]
247    'layer'				=> "\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [8]
248    'locale'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00", # [62]
249    'malloc'				=> "\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [25]
250    'misc'				=> "\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [12]
251    'missing'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00\x00", # [63]
252    'newline'				=> "\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [9]
253    'non_unicode'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00", # [48]
254    'nonchar'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00", # [49]
255    'numeric'				=> "\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [13]
256    'once'				=> "\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [14]
257    'overflow'				=> "\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [15]
258    'pack'				=> "\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [16]
259    'parenthesis'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [32]
260    'pipe'				=> "\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [10]
261    'portable'				=> "\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [17]
262    'precedence'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [33]
263    'printf'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [34]
264    'prototype'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [35]
265    'qw'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [36]
266    'recursion'				=> "\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [18]
267    'redefine'				=> "\x00\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [19]
268    'redundant'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00", # [64]
269    'regexp'				=> "\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [20]
270    'reserved'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [37]
271    'scalar'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80", # [79]
272    'semicolon'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [38]
273    'severe'				=> "\x00\x00\x00\x00\x00\xa8\x0a\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [21..25]
274    'shadow'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00", # [68]
275    'signal'				=> "\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [26]
276    'substr'				=> "\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [27]
277    'surrogate'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00", # [50]
278    'syntax'				=> "\x00\x00\x00\x00\x00\x00\x00\xaa\xaa\x2a\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00", # [28..38,47]
279    'syscalls'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00", # [57]
280    'taint'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [39]
281    'threads'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [40]
282    'uninitialized'			=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [41]
283    'unopened'				=> "\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [11]
284    'unpack'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x20\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [42]
285    'untie'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00", # [43]
286    'utf8'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x2a\x00\x00\x00\x00\x00\x00\x00", # [44,48..50]
287    'void'				=> "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00\x00", # [45]
288);
289
290# These are used by various things, including our own tests
291our $NONE				=  "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
292our $DEFAULT				=  "\x10\x01\x00\x00\x00\x50\x04\x00\x00\x00\x00\x00\x00\x51\x51\x15\x54\x54\x55\x15"; # [2,4,22,23,25,52,54..56,58..62,65..67,69..78]
293our $LAST_BIT				=  160 ;
294our $BYTES				=  20 ;
295
296sub Croaker
297{
298    require Carp; # this initializes %CarpInternal
299    local $Carp::CarpInternal{'warnings'};
300    delete $Carp::CarpInternal{'warnings'};
301    Carp::croak(@_);
302}
303
304sub _expand_bits {
305    my $bits = shift;
306    my $want_len = ($LAST_BIT + 7) >> 3;
307    my $len = length($bits);
308    if ($len != $want_len) {
309        if ($bits eq "") {
310            $bits = "\x00" x $want_len;
311        } elsif ($len > $want_len) {
312            substr $bits, $want_len, $len-$want_len, "";
313        } else {
314            my $x = vec($bits, $Offsets{all} >> 1, 2);
315            $x |= $x << 2;
316            $x |= $x << 4;
317            $bits .= chr($x) x ($want_len - $len);
318        }
319    }
320    return $bits;
321}
322
323sub _bits {
324    my $mask = shift ;
325    my $catmask ;
326    my $fatal = 0 ;
327    my $no_fatal = 0 ;
328
329    $mask = _expand_bits($mask);
330    foreach my $word ( @_ ) {
331        if ($word eq 'FATAL') {
332            $fatal = 1;
333            $no_fatal = 0;
334        }
335        elsif ($word eq 'NONFATAL') {
336            $fatal = 0;
337            $no_fatal = 1;
338        }
339        elsif ($catmask = $Bits{$word}) {
340            $mask |= $catmask ;
341            $mask |= $DeadBits{$word} if $fatal ;
342            $mask = ~(~$mask | $DeadBits{$word}) if $no_fatal ;
343        }
344        else
345          { Croaker("Unknown warnings category '$word'")}
346    }
347
348    return $mask ;
349}
350
351sub bits
352{
353    # called from B::Deparse.pm
354    push @_, 'all' unless @_ ;
355    return _bits("", @_) ;
356}
357
358sub import
359{
360    my $invocant = shift;
361
362    # append 'all' when implied (empty import list or after a lone
363    # "FATAL" or "NONFATAL")
364    push @_, 'all'
365        if !@_ || (@_==1 && ($_[0] eq 'FATAL' || $_[0] eq 'NONFATAL'));
366
367    my @fatal = ();
368    foreach my $warning (@_) {
369        if($warning =~ /^(NON)?FATAL$/) {
370            @fatal = ($warning);
371        } elsif(substr($warning, 0, 1) ne '-') {
372            my $mask = ${^WARNING_BITS} // ($^W ? $Bits{all} : $DEFAULT) ;
373            ${^WARNING_BITS} = _bits($mask, @fatal, $warning);
374        } else {
375            $invocant->unimport(substr($warning, 1));
376        }
377    }
378}
379
380sub unimport
381{
382    shift;
383
384    my $catmask ;
385    my $mask = ${^WARNING_BITS} // ($^W ? $Bits{all} : $DEFAULT) ;
386
387    # append 'all' when implied (empty import list or after a lone "FATAL")
388    push @_, 'all' if !@_ || @_==1 && $_[0] eq 'FATAL';
389
390    $mask = _expand_bits($mask);
391    foreach my $word ( @_ ) {
392        if ($word eq 'FATAL') {
393            next;
394        }
395        elsif ($catmask = $Bits{$word}) {
396            $mask = ~(~$mask | $catmask | $DeadBits{$word});
397        }
398        else
399          { Croaker("Unknown warnings category '$word'")}
400    }
401
402    ${^WARNING_BITS} = $mask ;
403}
404
405my %builtin_type; @builtin_type{qw(SCALAR ARRAY HASH CODE REF GLOB LVALUE Regexp)} = ();
406
407sub LEVEL () { 8 };
408sub MESSAGE () { 4 };
409sub FATAL () { 2 };
410sub NORMAL () { 1 };
411
412sub __chk
413{
414    my $category ;
415    my $offset ;
416    my $isobj = 0 ;
417    my $wanted = shift;
418    my $has_message = $wanted & MESSAGE;
419    my $has_level   = $wanted & LEVEL  ;
420
421    if ($has_level) {
422        if (@_ != ($has_message ? 3 : 2)) {
423            my $sub = (caller 1)[3];
424            my $syntax = $has_message
425                ? "category, level, 'message'"
426                : 'category, level';
427            Croaker("Usage: $sub($syntax)");
428        }
429    }
430    elsif (not @_ == 1 || @_ == ($has_message ? 2 : 0)) {
431        my $sub = (caller 1)[3];
432        my $syntax = $has_message ? "[category,] 'message'" : '[category]';
433        Croaker("Usage: $sub($syntax)");
434    }
435
436    my $message = pop if $has_message;
437
438    if (@_) {
439        # check the category supplied.
440        $category = shift ;
441        if (my $type = ref $category) {
442            Croaker("not an object")
443                if exists $builtin_type{$type};
444            $category = $type;
445            $isobj = 1 ;
446        }
447        $offset = $Offsets{$category};
448        Croaker("Unknown warnings category '$category'")
449            unless defined $offset;
450    }
451    else {
452        $category = (caller(1))[0] ;
453        $offset = $Offsets{$category};
454        Croaker("package '$category' not registered for warnings")
455            unless defined $offset ;
456    }
457
458    my $i;
459
460    if ($isobj) {
461        my $pkg;
462        $i = 2;
463        while (do { { package DB; $pkg = (caller($i++))[0] } } ) {
464            last unless @DB::args && $DB::args[0] =~ /^$category=/ ;
465        }
466        $i -= 2 ;
467    }
468    elsif ($has_level) {
469        $i = 2 + shift;
470    }
471    else {
472        $i = _error_loc(); # see where Carp will allocate the error
473    }
474
475    # Default to 0 if caller returns nothing.  Default to $DEFAULT if it
476    # explicitly returns undef.
477    my(@callers_bitmask) = (caller($i))[9] ;
478    my $callers_bitmask =
479         @callers_bitmask ? $callers_bitmask[0] // $DEFAULT : 0 ;
480    length($callers_bitmask) > ($offset >> 3) or $offset = $Offsets{all};
481
482    my @results;
483    foreach my $type (FATAL, NORMAL) {
484        next unless $wanted & $type;
485
486        push @results, vec($callers_bitmask, $offset + $type - 1, 1);
487    }
488
489    # &enabled and &fatal_enabled
490    return $results[0] unless $has_message;
491
492    # &warnif, and the category is neither enabled as warning nor as fatal
493    return if ($wanted & (NORMAL | FATAL | MESSAGE))
494                      == (NORMAL | FATAL | MESSAGE)
495        && !($results[0] || $results[1]);
496
497    # If we have an explicit level, bypass Carp.
498    if ($has_level and @callers_bitmask) {
499        # logic copied from util.c:mess_sv
500        my $stuff = " at " . join " line ", (caller $i)[1,2];
501        $stuff .= sprintf ", <%s> %s %d",
502                           *${^LAST_FH}{NAME},
503                           ($/ eq "\n" ? "line" : "chunk"), $.
504            if $. && ${^LAST_FH};
505        die "$message$stuff.\n" if $results[0];
506        return warn "$message$stuff.\n";
507    }
508
509    require Carp;
510    Carp::croak($message) if $results[0];
511    # will always get here for &warn. will only get here for &warnif if the
512    # category is enabled
513    Carp::carp($message);
514}
515
516sub _mkMask
517{
518    my ($bit) = @_;
519    my $mask = "";
520
521    vec($mask, $bit, 1) = 1;
522    return $mask;
523}
524
525sub register_categories
526{
527    my @names = @_;
528
529    for my $name (@names) {
530        if (! defined $Bits{$name}) {
531            $Offsets{$name}  = $LAST_BIT;
532            $Bits{$name}     = _mkMask($LAST_BIT++);
533            $DeadBits{$name} = _mkMask($LAST_BIT++);
534            if (length($Bits{$name}) > length($Bits{all})) {
535                $Bits{all} .= "\x55";
536                $DeadBits{all} .= "\xaa";
537            }
538        }
539    }
540}
541
542sub _error_loc {
543    require Carp;
544    goto &Carp::short_error_loc; # don't introduce another stack frame
545}
546
547sub enabled
548{
549    return __chk(NORMAL, @_);
550}
551
552sub fatal_enabled
553{
554    return __chk(FATAL, @_);
555}
556
557sub warn
558{
559    return __chk(FATAL | MESSAGE, @_);
560}
561
562sub warnif
563{
564    return __chk(NORMAL | FATAL | MESSAGE, @_);
565}
566
567sub enabled_at_level
568{
569    return __chk(NORMAL | LEVEL, @_);
570}
571
572sub fatal_enabled_at_level
573{
574    return __chk(FATAL | LEVEL, @_);
575}
576
577sub warn_at_level
578{
579    return __chk(FATAL | MESSAGE | LEVEL, @_);
580}
581
582sub warnif_at_level
583{
584    return __chk(NORMAL | FATAL | MESSAGE | LEVEL, @_);
585}
586
587# These are not part of any public interface, so we can delete them to save
588# space.
589delete @warnings::{qw(NORMAL FATAL MESSAGE LEVEL)};
590
5911;
592__END__
593
594=head1 NAME
595
596warnings - Perl pragma to control optional warnings
597
598=head1 SYNOPSIS
599
600    use warnings;
601    no warnings;
602
603    # Standard warnings are enabled by use v5.35 or above
604    use v5.35;
605
606    use warnings "all";
607    no warnings "uninitialized";
608
609    # or equivalent to those last two ...
610    use warnings qw(all -uninitialized);
611
612    use warnings::register;
613    if (warnings::enabled()) {
614        warnings::warn("some warning");
615    }
616
617    if (warnings::enabled("void")) {
618        warnings::warn("void", "some warning");
619    }
620
621    if (warnings::enabled($object)) {
622        warnings::warn($object, "some warning");
623    }
624
625    warnings::warnif("some warning");
626    warnings::warnif("void", "some warning");
627    warnings::warnif($object, "some warning");
628
629=head1 DESCRIPTION
630
631The C<warnings> pragma gives control over which warnings are enabled in
632which parts of a Perl program.  It's a more flexible alternative for
633both the command line flag B<-w> and the equivalent Perl variable,
634C<$^W>.
635
636This pragma works just like the C<strict> pragma.
637This means that the scope of the warning pragma is limited to the
638enclosing block.  It also means that the pragma setting will not
639leak across files (via C<use>, C<require> or C<do>).  This allows
640authors to independently define the degree of warning checks that will
641be applied to their module.
642
643By default, optional warnings are disabled, so any legacy code that
644doesn't attempt to control the warnings will work unchanged.
645
646All warnings are enabled in a block by either of these:
647
648    use warnings;
649    use warnings 'all';
650
651Similarly all warnings are disabled in a block by either of these:
652
653    no warnings;
654    no warnings 'all';
655
656For example, consider the code below:
657
658    use warnings;
659    my @x;
660    {
661        no warnings;
662        my $y = @x[0];
663    }
664    my $z = @x[0];
665
666The code in the enclosing block has warnings enabled, but the inner
667block has them disabled.  In this case that means the assignment to the
668scalar C<$z> will trip the C<"Scalar value @x[0] better written as $x[0]">
669warning, but the assignment to the scalar C<$y> will not.
670
671All warnings are enabled automatically within the scope of
672a C<L<use v5.35|perlfunc/use VERSION>> (or higher) declaration.
673
674=head2 Default Warnings and Optional Warnings
675
676Before the introduction of lexical warnings, Perl had two classes of
677warnings: mandatory and optional.
678
679As its name suggests, if your code tripped a mandatory warning, you
680would get a warning whether you wanted it or not.
681For example, the code below would always produce an C<"isn't numeric">
682warning about the "2:".
683
684    my $x = "2:" + 3;
685
686With the introduction of lexical warnings, mandatory warnings now become
687I<default> warnings.  The difference is that although the previously
688mandatory warnings are still enabled by default, they can then be
689subsequently enabled or disabled with the lexical warning pragma.  For
690example, in the code below, an C<"isn't numeric"> warning will only
691be reported for the C<$x> variable.
692
693    my $x = "2:" + 3;
694    no warnings;
695    my $y = "2:" + 3;
696
697Note that neither the B<-w> flag or the C<$^W> can be used to
698disable/enable default warnings.  They are still mandatory in this case.
699
700=head2 "Negative warnings"
701
702As a convenience, you can (as of Perl 5.34) pass arguments to the
703C<import()> method both positively and negatively. Negative warnings
704are those with a C<-> sign prepended to their names; positive warnings
705are anything else. This lets you turn on some warnings and turn off
706others in one command. So, assuming that you've already turned on a
707bunch of warnings but want to tweak them a bit in some block, you can
708do this:
709
710    {
711        use warnings qw(uninitialized -redefine);
712        ...
713    }
714
715which is equivalent to:
716
717    {
718        use warnings qw(uninitialized);
719        no warnings qw(redefine);
720        ...
721    }
722
723The argument list is processed in the order you specify. So, for example, if you
724don't want to be warned about use of experimental features, except for C<somefeature>
725that you really dislike, you can say this:
726
727    use warnings qw(all -experimental experimental::somefeature);
728
729which is equivalent to:
730
731    use warnings 'all';
732    no warnings  'experimental';
733    use warnings 'experimental::somefeature';
734
735=head2 What's wrong with B<-w> and C<$^W>
736
737Although very useful, the big problem with using B<-w> on the command
738line to enable warnings is that it is all or nothing.  Take the typical
739scenario when you are writing a Perl program.  Parts of the code you
740will write yourself, but it's very likely that you will make use of
741pre-written Perl modules.  If you use the B<-w> flag in this case, you
742end up enabling warnings in pieces of code that you haven't written.
743
744Similarly, using C<$^W> to either disable or enable blocks of code is
745fundamentally flawed.  For a start, say you want to disable warnings in
746a block of code.  You might expect this to be enough to do the trick:
747
748     {
749         local ($^W) = 0;
750         my $x =+ 2;
751         my $y; chop $y;
752     }
753
754When this code is run with the B<-w> flag, a warning will be produced
755for the C<$x> line:  C<"Reversed += operator">.
756
757The problem is that Perl has both compile-time and run-time warnings.  To
758disable compile-time warnings you need to rewrite the code like this:
759
760     {
761         BEGIN { $^W = 0 }
762         my $x =+ 2;
763         my $y; chop $y;
764     }
765
766And note that unlike the first example, this will permanently set C<$^W>
767since it cannot both run during compile-time and be localized to a
768run-time block.
769
770The other big problem with C<$^W> is the way you can inadvertently
771change the warning setting in unexpected places in your code.  For example,
772when the code below is run (without the B<-w> flag), the second call
773to C<doit> will trip a C<"Use of uninitialized value"> warning, whereas
774the first will not.
775
776    sub doit
777    {
778        my $y; chop $y;
779    }
780
781    doit();
782
783    {
784        local ($^W) = 1;
785        doit()
786    }
787
788This is a side-effect of C<$^W> being dynamically scoped.
789
790Lexical warnings get around these limitations by allowing finer control
791over where warnings can or can't be tripped.
792
793=head2 Controlling Warnings from the Command Line
794
795There are three Command Line flags that can be used to control when
796warnings are (or aren't) produced:
797
798=over 5
799
800=item B<-w>
801X<-w>
802
803This is  the existing flag.  If the lexical warnings pragma is B<not>
804used in any of your code, or any of the modules that you use, this flag
805will enable warnings everywhere.  See L</Backward Compatibility> for
806details of how this flag interacts with lexical warnings.
807
808=item B<-W>
809X<-W>
810
811If the B<-W> flag is used on the command line, it will enable all warnings
812throughout the program regardless of whether warnings were disabled
813locally using C<no warnings> or C<$^W =0>.
814This includes all files that get
815included via C<use>, C<require> or C<do>.
816Think of it as the Perl equivalent of the "lint" command.
817
818=item B<-X>
819X<-X>
820
821Does the exact opposite to the B<-W> flag, i.e. it disables all warnings.
822
823=back
824
825=head2 Backward Compatibility
826
827If you are used to working with a version of Perl prior to the
828introduction of lexically scoped warnings, or have code that uses both
829lexical warnings and C<$^W>, this section will describe how they interact.
830
831How Lexical Warnings interact with B<-w>/C<$^W>:
832
833=over 5
834
835=item 1.
836
837If none of the three command line flags (B<-w>, B<-W> or B<-X>) that
838control warnings is used and neither C<$^W> nor the C<warnings> pragma
839are used, then default warnings will be enabled and optional warnings
840disabled.
841This means that legacy code that doesn't attempt to control the warnings
842will work unchanged.
843
844=item 2.
845
846The B<-w> flag just sets the global C<$^W> variable as in 5.005.  This
847means that any legacy code that currently relies on manipulating C<$^W>
848to control warning behavior will still work as is.
849
850=item 3.
851
852Apart from now being a boolean, the C<$^W> variable operates in exactly
853the same horrible uncontrolled global way, except that it cannot
854disable/enable default warnings.
855
856=item 4.
857
858If a piece of code is under the control of the C<warnings> pragma,
859both the C<$^W> variable and the B<-w> flag will be ignored for the
860scope of the lexical warning.
861
862=item 5.
863
864The only way to override a lexical warnings setting is with the B<-W>
865or B<-X> command line flags.
866
867=back
868
869The combined effect of 3 & 4 is that it will allow code which uses
870the C<warnings> pragma to control the warning behavior of $^W-type
871code (using a C<local $^W=0>) if it really wants to, but not vice-versa.
872
873=head2 Category Hierarchy
874X<warning, categories>
875
876A hierarchy of "categories" have been defined to allow groups of warnings
877to be enabled/disabled in isolation.
878
879The current hierarchy is:
880
881    all -+
882         |
883         +- closure
884         |
885         +- deprecated
886         |
887         +- exiting
888         |
889         +- experimental --+
890         |                 |
891         |                 +- experimental::alpha_assertions
892         |                 |
893         |                 +- experimental::args_array_with_signatures
894         |                 |
895         |                 +- experimental::bitwise
896         |                 |
897         |                 +- experimental::builtin
898         |                 |
899         |                 +- experimental::const_attr
900         |                 |
901         |                 +- experimental::declared_refs
902         |                 |
903         |                 +- experimental::defer
904         |                 |
905         |                 +- experimental::extra_paired_delimiters
906         |                 |
907         |                 +- experimental::for_list
908         |                 |
909         |                 +- experimental::isa
910         |                 |
911         |                 +- experimental::lexical_subs
912         |                 |
913         |                 +- experimental::postderef
914         |                 |
915         |                 +- experimental::private_use
916         |                 |
917         |                 +- experimental::re_strict
918         |                 |
919         |                 +- experimental::refaliasing
920         |                 |
921         |                 +- experimental::regex_sets
922         |                 |
923         |                 +- experimental::script_run
924         |                 |
925         |                 +- experimental::signatures
926         |                 |
927         |                 +- experimental::smartmatch
928         |                 |
929         |                 +- experimental::try
930         |                 |
931         |                 +- experimental::uniprop_wildcards
932         |                 |
933         |                 +- experimental::vlb
934         |
935         +- glob
936         |
937         +- imprecision
938         |
939         +- io ------------+
940         |                 |
941         |                 +- closed
942         |                 |
943         |                 +- exec
944         |                 |
945         |                 +- layer
946         |                 |
947         |                 +- newline
948         |                 |
949         |                 +- pipe
950         |                 |
951         |                 +- syscalls
952         |                 |
953         |                 +- unopened
954         |
955         +- locale
956         |
957         +- misc
958         |
959         +- missing
960         |
961         +- numeric
962         |
963         +- once
964         |
965         +- overflow
966         |
967         +- pack
968         |
969         +- portable
970         |
971         +- recursion
972         |
973         +- redefine
974         |
975         +- redundant
976         |
977         +- regexp
978         |
979         +- scalar
980         |
981         +- severe --------+
982         |                 |
983         |                 +- debugging
984         |                 |
985         |                 +- inplace
986         |                 |
987         |                 +- internal
988         |                 |
989         |                 +- malloc
990         |
991         +- shadow
992         |
993         +- signal
994         |
995         +- substr
996         |
997         +- syntax --------+
998         |                 |
999         |                 +- ambiguous
1000         |                 |
1001         |                 +- bareword
1002         |                 |
1003         |                 +- digit
1004         |                 |
1005         |                 +- illegalproto
1006         |                 |
1007         |                 +- parenthesis
1008         |                 |
1009         |                 +- precedence
1010         |                 |
1011         |                 +- printf
1012         |                 |
1013         |                 +- prototype
1014         |                 |
1015         |                 +- qw
1016         |                 |
1017         |                 +- reserved
1018         |                 |
1019         |                 +- semicolon
1020         |
1021         +- taint
1022         |
1023         +- threads
1024         |
1025         +- uninitialized
1026         |
1027         +- unpack
1028         |
1029         +- untie
1030         |
1031         +- utf8 ----------+
1032         |                 |
1033         |                 +- non_unicode
1034         |                 |
1035         |                 +- nonchar
1036         |                 |
1037         |                 +- surrogate
1038         |
1039         +- void
1040
1041Just like the "strict" pragma any of these categories can be combined
1042
1043    use warnings qw(void redefine);
1044    no warnings qw(io syntax untie);
1045
1046Also like the "strict" pragma, if there is more than one instance of the
1047C<warnings> pragma in a given scope the cumulative effect is additive.
1048
1049    use warnings qw(void); # only "void" warnings enabled
1050    ...
1051    use warnings qw(io);   # only "void" & "io" warnings enabled
1052    ...
1053    no warnings qw(void);  # only "io" warnings enabled
1054
1055To determine which category a specific warning has been assigned to see
1056L<perldiag>.
1057
1058Note: Before Perl 5.8.0, the lexical warnings category "deprecated" was a
1059sub-category of the "syntax" category.  It is now a top-level category
1060in its own right.
1061
1062Note: Before 5.21.0, the "missing" lexical warnings category was
1063internally defined to be the same as the "uninitialized" category. It
1064is now a top-level category in its own right.
1065
1066=head2 Fatal Warnings
1067X<warning, fatal>
1068
1069The presence of the word "FATAL" in the category list will escalate
1070warnings in those categories into fatal errors in that lexical scope.
1071
1072B<NOTE:> FATAL warnings should be used with care, particularly
1073C<< FATAL => 'all' >>.
1074
1075Libraries using L<warnings::warn|/FUNCTIONS> for custom warning categories
1076generally don't expect L<warnings::warn|/FUNCTIONS> to be fatal and can wind up
1077in an unexpected state as a result.  For XS modules issuing categorized
1078warnings, such unanticipated exceptions could also expose memory leak bugs.
1079
1080Moreover, the Perl interpreter itself has had serious bugs involving
1081fatalized warnings.  For a summary of resolved and unresolved problems as
1082of January 2015, please see
1083L<this perl5-porters post|http://www.nntp.perl.org/group/perl.perl5.porters/2015/01/msg225235.html>.
1084
1085While some developers find fatalizing some warnings to be a useful
1086defensive programming technique, using C<< FATAL => 'all' >> to fatalize
1087all possible warning categories -- including custom ones -- is particularly
1088risky.  Therefore, the use of C<< FATAL => 'all' >> is
1089L<discouraged|perlpolicy/discouraged>.
1090
1091The L<strictures|strictures/VERSION-2> module on CPAN offers one example of
1092a warnings subset that the module's authors believe is relatively safe to
1093fatalize.
1094
1095B<NOTE:> Users of FATAL warnings, especially those using
1096C<< FATAL => 'all' >>, should be fully aware that they are risking future
1097portability of their programs by doing so.  Perl makes absolutely no
1098commitments to not introduce new warnings or warnings categories in the
1099future; indeed, we explicitly reserve the right to do so.  Code that may
1100not warn now may warn in a future release of Perl if the Perl5 development
1101team deems it in the best interests of the community to do so.  Should code
1102using FATAL warnings break due to the introduction of a new warning we will
1103NOT consider it an incompatible change.  Users of FATAL warnings should
1104take special caution during upgrades to check to see if their code triggers
1105any new warnings and should pay particular attention to the fine print of
1106the documentation of the features they use to ensure they do not exploit
1107features that are documented as risky, deprecated, or unspecified, or where
1108the documentation says "so don't do that", or anything with the same sense
1109and spirit.  Use of such features in combination with FATAL warnings is
1110ENTIRELY AT THE USER'S RISK.
1111
1112The following documentation describes how to use FATAL warnings but the
1113perl5 porters strongly recommend that you understand the risks before doing
1114so, especially for library code intended for use by others, as there is no
1115way for downstream users to change the choice of fatal categories.
1116
1117In the code below, the use of C<time>, C<length>
1118and C<join> can all produce a C<"Useless use of xxx in void context">
1119warning.
1120
1121    use warnings;
1122
1123    time;
1124
1125    {
1126        use warnings FATAL => qw(void);
1127        length "abc";
1128    }
1129
1130    join "", 1,2,3;
1131
1132    print "done\n";
1133
1134When run it produces this output
1135
1136    Useless use of time in void context at fatal line 3.
1137    Useless use of length in void context at fatal line 7.
1138
1139The scope where C<length> is used has escalated the C<void> warnings
1140category into a fatal error, so the program terminates immediately when it
1141encounters the warning.
1142
1143To explicitly turn off a "FATAL" warning you just disable the warning
1144it is associated with.  So, for example, to disable the "void" warning
1145in the example above, either of these will do the trick:
1146
1147    no warnings qw(void);
1148    no warnings FATAL => qw(void);
1149
1150If you want to downgrade a warning that has been escalated into a fatal
1151error back to a normal warning, you can use the "NONFATAL" keyword.  For
1152example, the code below will promote all warnings into fatal errors,
1153except for those in the "syntax" category.
1154
1155    use warnings FATAL => 'all', NONFATAL => 'syntax';
1156
1157As of Perl 5.20, instead of C<< use warnings FATAL => 'all'; >> you can
1158use:
1159
1160   use v5.20;       # Perl 5.20 or greater is required for the following
1161   use warnings 'FATAL';  # short form of "use warnings FATAL => 'all';"
1162
1163However, you should still heed the guidance earlier in this section against
1164using C<< use warnings FATAL => 'all'; >>.
1165
1166If you want your program to be compatible with versions of Perl before
11675.20, you must use C<< use warnings FATAL => 'all'; >> instead.  (In
1168previous versions of Perl, the behavior of the statements
1169C<< use warnings 'FATAL'; >>, C<< use warnings 'NONFATAL'; >> and
1170C<< no warnings 'FATAL'; >> was unspecified; they did not behave as if
1171they included the C<< => 'all' >> portion.  As of 5.20, they do.)
1172
1173=head2 Reporting Warnings from a Module
1174X<warning, reporting> X<warning, registering>
1175
1176The C<warnings> pragma provides a number of functions that are useful for
1177module authors.  These are used when you want to report a module-specific
1178warning to a calling module has enabled warnings via the C<warnings>
1179pragma.
1180
1181Consider the module C<MyMod::Abc> below.
1182
1183    package MyMod::Abc;
1184
1185    use warnings::register;
1186
1187    sub open {
1188        my $path = shift;
1189        if ($path !~ m#^/#) {
1190            warnings::warn("changing relative path to /var/abc")
1191                if warnings::enabled();
1192            $path = "/var/abc/$path";
1193        }
1194    }
1195
1196    1;
1197
1198The call to C<warnings::register> will create a new warnings category
1199called "MyMod::Abc", i.e. the new category name matches the current
1200package name.  The C<open> function in the module will display a warning
1201message if it gets given a relative path as a parameter.  This warnings
1202will only be displayed if the code that uses C<MyMod::Abc> has actually
1203enabled them with the C<warnings> pragma like below.
1204
1205    use MyMod::Abc;
1206    use warnings 'MyMod::Abc';
1207    ...
1208    abc::open("../fred.txt");
1209
1210It is also possible to test whether the pre-defined warnings categories are
1211set in the calling module with the C<warnings::enabled> function.  Consider
1212this snippet of code:
1213
1214    package MyMod::Abc;
1215
1216    sub open {
1217        if (warnings::enabled("deprecated")) {
1218            warnings::warn("deprecated",
1219                           "open is deprecated, use new instead");
1220        }
1221        new(@_);
1222    }
1223
1224    sub new
1225    ...
1226    1;
1227
1228The function C<open> has been deprecated, so code has been included to
1229display a warning message whenever the calling module has (at least) the
1230"deprecated" warnings category enabled.  Something like this, say.
1231
1232    use warnings 'deprecated';
1233    use MyMod::Abc;
1234    ...
1235    MyMod::Abc::open($filename);
1236
1237Either the C<warnings::warn> or C<warnings::warnif> function should be
1238used to actually display the warnings message.  This is because they can
1239make use of the feature that allows warnings to be escalated into fatal
1240errors.  So in this case
1241
1242    use MyMod::Abc;
1243    use warnings FATAL => 'MyMod::Abc';
1244    ...
1245    MyMod::Abc::open('../fred.txt');
1246
1247the C<warnings::warnif> function will detect this and die after
1248displaying the warning message.
1249
1250The three warnings functions, C<warnings::warn>, C<warnings::warnif>
1251and C<warnings::enabled> can optionally take an object reference in place
1252of a category name.  In this case the functions will use the class name
1253of the object as the warnings category.
1254
1255Consider this example:
1256
1257    package Original;
1258
1259    no warnings;
1260    use warnings::register;
1261
1262    sub new
1263    {
1264        my $class = shift;
1265        bless [], $class;
1266    }
1267
1268    sub check
1269    {
1270        my $self = shift;
1271        my $value = shift;
1272
1273        if ($value % 2 && warnings::enabled($self))
1274          { warnings::warn($self, "Odd numbers are unsafe") }
1275    }
1276
1277    sub doit
1278    {
1279        my $self = shift;
1280        my $value = shift;
1281        $self->check($value);
1282        # ...
1283    }
1284
1285    1;
1286
1287    package Derived;
1288
1289    use warnings::register;
1290    use Original;
1291    our @ISA = qw( Original );
1292    sub new
1293    {
1294        my $class = shift;
1295        bless [], $class;
1296    }
1297
1298
1299    1;
1300
1301The code below makes use of both modules, but it only enables warnings from
1302C<Derived>.
1303
1304    use Original;
1305    use Derived;
1306    use warnings 'Derived';
1307    my $x = Original->new();
1308    $x->doit(1);
1309    my $y = Derived->new();
1310    $x->doit(1);
1311
1312When this code is run only the C<Derived> object, C<$y>, will generate
1313a warning.
1314
1315    Odd numbers are unsafe at main.pl line 7
1316
1317Notice also that the warning is reported at the line where the object is first
1318used.
1319
1320When registering new categories of warning, you can supply more names to
1321warnings::register like this:
1322
1323    package MyModule;
1324    use warnings::register qw(format precision);
1325
1326    ...
1327
1328    warnings::warnif('MyModule::format', '...');
1329
1330=head1 FUNCTIONS
1331
1332Note: The functions with names ending in C<_at_level> were added in Perl
13335.28.
1334
1335=over 4
1336
1337=item use warnings::register
1338
1339Creates a new warnings category with the same name as the package where
1340the call to the pragma is used.
1341
1342=item warnings::enabled()
1343
1344Use the warnings category with the same name as the current package.
1345
1346Return TRUE if that warnings category is enabled in the calling module.
1347Otherwise returns FALSE.
1348
1349=item warnings::enabled($category)
1350
1351Return TRUE if the warnings category, C<$category>, is enabled in the
1352calling module.
1353Otherwise returns FALSE.
1354
1355=item warnings::enabled($object)
1356
1357Use the name of the class for the object reference, C<$object>, as the
1358warnings category.
1359
1360Return TRUE if that warnings category is enabled in the first scope
1361where the object is used.
1362Otherwise returns FALSE.
1363
1364=item warnings::enabled_at_level($category, $level)
1365
1366Like C<warnings::enabled>, but $level specifies the exact call frame, 0
1367being the immediate caller.
1368
1369=item warnings::fatal_enabled()
1370
1371Return TRUE if the warnings category with the same name as the current
1372package has been set to FATAL in the calling module.
1373Otherwise returns FALSE.
1374
1375=item warnings::fatal_enabled($category)
1376
1377Return TRUE if the warnings category C<$category> has been set to FATAL in
1378the calling module.
1379Otherwise returns FALSE.
1380
1381=item warnings::fatal_enabled($object)
1382
1383Use the name of the class for the object reference, C<$object>, as the
1384warnings category.
1385
1386Return TRUE if that warnings category has been set to FATAL in the first
1387scope where the object is used.
1388Otherwise returns FALSE.
1389
1390=item warnings::fatal_enabled_at_level($category, $level)
1391
1392Like C<warnings::fatal_enabled>, but $level specifies the exact call frame,
13930 being the immediate caller.
1394
1395=item warnings::warn($message)
1396
1397Print C<$message> to STDERR.
1398
1399Use the warnings category with the same name as the current package.
1400
1401If that warnings category has been set to "FATAL" in the calling module
1402then die. Otherwise return.
1403
1404=item warnings::warn($category, $message)
1405
1406Print C<$message> to STDERR.
1407
1408If the warnings category, C<$category>, has been set to "FATAL" in the
1409calling module then die. Otherwise return.
1410
1411=item warnings::warn($object, $message)
1412
1413Print C<$message> to STDERR.
1414
1415Use the name of the class for the object reference, C<$object>, as the
1416warnings category.
1417
1418If that warnings category has been set to "FATAL" in the scope where C<$object>
1419is first used then die. Otherwise return.
1420
1421=item warnings::warn_at_level($category, $level, $message)
1422
1423Like C<warnings::warn>, but $level specifies the exact call frame,
14240 being the immediate caller.
1425
1426=item warnings::warnif($message)
1427
1428Equivalent to:
1429
1430    if (warnings::enabled())
1431      { warnings::warn($message) }
1432
1433=item warnings::warnif($category, $message)
1434
1435Equivalent to:
1436
1437    if (warnings::enabled($category))
1438      { warnings::warn($category, $message) }
1439
1440=item warnings::warnif($object, $message)
1441
1442Equivalent to:
1443
1444    if (warnings::enabled($object))
1445      { warnings::warn($object, $message) }
1446
1447=item warnings::warnif_at_level($category, $level, $message)
1448
1449Like C<warnings::warnif>, but $level specifies the exact call frame,
14500 being the immediate caller.
1451
1452=item warnings::register_categories(@names)
1453
1454This registers warning categories for the given names and is primarily for
1455use by the warnings::register pragma.
1456
1457=back
1458
1459See also L<perlmodlib/Pragmatic Modules> and L<perldiag>.
1460
1461=cut
1462
1463# ex: set ro:
1464