Added C23 attributes to C lexer.

Based on contribution from Samuel Marquis.

docs/thanks.md

@@ -59,6 +59,7 @@ and better over the years.
 * Robert Gieseke
 * Roberto Ierusalimschy
 * S\. Gilles
+* Samuel Marquis
 * Simeon Maryasin
 * Snoopy
 * Stéphane Rivière

lexers/ansi_c.lua

@@ -36,8 +36,9 @@ lex:add_rule('identifier', lex:tag(lexer.IDENTIFIER, lexer.word))
 
 -- Comments.
 local line_comment = lexer.to_eol('//', true)
+local ws = S(' \t')^0
 local block_comment = lexer.range('/*', '*/') +
-  lexer.range('#if' * S(' \t')^0 * '0' * lexer.space, '#endif')
+  lexer.range('#if' * ws * '0' * lexer.space, '#endif')
 lex:add_rule('comment', lex:tag(lexer.COMMENT, line_comment + block_comment))
 
 -- Numbers.
@@ -46,11 +47,18 @@ local float = lexer.float * P('f')^-1
 lex:add_rule('number', lex:tag(lexer.NUMBER, float + integer))
 
 -- Preprocessor.
-local include = lex:tag(lexer.PREPROCESSOR, '#' * S('\t ')^0 * 'include') *
+local include = lex:tag(lexer.PREPROCESSOR, '#' * ws * 'include') *
   (lex:get_rule('whitespace') * lex:tag(lexer.STRING, lexer.range('<', '>', true)))^-1
-local preproc = lex:tag(lexer.PREPROCESSOR, '#' * S('\t ')^0 * lex:word_match(lexer.PREPROCESSOR))
+local preproc = lex:tag(lexer.PREPROCESSOR, '#' * ws * lex:word_match(lexer.PREPROCESSOR))
 lex:add_rule('preprocessor', include + preproc)
 
+-- Attributes.
+local standard_attr = lex:word_match(lexer.ATTRIBUTE)
+local non_standard_attr = lexer.word * '::' * lexer.word
+local attr_args = lexer.range('(', ')')
+local attr = (non_standard_attr + standard_attr) * attr_args^-1
+lex:add_rule('attribute', lex:tag(lexer.ATTRIBUTE, '[[' * attr * (ws * ',' * ws * attr)^0 * ']]'))
+
 -- Operators.
 lex:add_rule('operator', lex:tag(lexer.OPERATOR, S('+-/*%<>~!=^&|?~:;,.()[]{}')))
 
@@ -194,6 +202,12 @@ lex:set_word_list(lexer.PREPROCESSOR, {
   'undef'
 })
 
+lex:set_word_list(lexer.ATTRIBUTE, {
+  -- C23
+  'deprecated', 'fallthrough', 'nodiscard', 'maybe_unused', 'noreturn', '_Noreturn', 'unsequenced',
+  'reproducible'
+})
+
 lexer.property['scintillua.comment'] = '//'
 
 return lex