cgen: define perror

Author: medvednikov

vlib/v/gen/c/cheaders.v

@@ -418,6 +418,7 @@ int sprintf(char *str, const char *format, ...);
 int sscanf(const char *str, const char *format, ...);
 int scanf(const char *format, ...);
 int puts(const char *str);
+void perror(const char *str);
 int fputs(const char *str, FILE *stream);
 int getchar(void);
 int putchar(int ch);
@@ -457,6 +458,7 @@ int remove(const char *path);
 int rename(const char *old_path, const char *new_path);
 char *realpath(const char *path, char *resolved_path);
 void qsort(void *base, size_t items, size_t item_size, qsort_callback_func cb);
+int strcmp(const char *left, const char *right);
 size_t strlen(const char *str);
 char *strerror(int errnum);
 void *memcpy(void *dest, const void *src, size_t n);

vlib/v/gen/c/cheaders_manual_stdlib_decls_test.v

@@ -28,6 +28,8 @@ fn test_default_c_prelude_uses_manual_stdio_stdlib_string_and_stdarg_decls() {
 
 	assert generated_c.contains('int vsnprintf(char *str, size_t size, const char *format, va_list ap);'), generated_c
 
+	assert generated_c.contains('void perror(const char *str);'), generated_c
+	assert generated_c.contains('int strcmp(const char *left, const char *right);'), generated_c
 	assert generated_c.contains('extern FILE* stdout;'), generated_c
 	assert generated_c.contains('#define stdout (__acrt_iob_func(1))'), generated_c
 }
@@ -43,3 +45,19 @@ fn test_manual_stdio_decls_do_not_conflict_with_later_stdio_includes() {
 	res := os.execute(cmd)
 	assert res.exit_code == 0, '${cmd}\n${res.output}'
 }
+
+fn test_manual_stdio_decls_allow_headerless_perror_declarations() {
+	tmp_dir := os.join_path(os.vtmp_dir(), 'cheaders_manual_stdlib_perror_${os.getpid()}')
+	os.mkdir_all(tmp_dir)!
+	defer {
+		os.rmdir_all(tmp_dir) or {}
+	}
+	source_path := os.join_path(tmp_dir, 'c_perror.v')
+	os.write_file(source_path,
+
+		['fn C.perror(message &char)', '', 'fn main() {', "\tC.perror(c'')", '}'].join('\n') + '\n')!
+	output_path := os.join_path(tmp_dir, 'c_perror')
+	cmd := '${os.quoted_path(cheaders_manual_stdlib_vexe)} -o ${os.quoted_path(output_path)} ${os.quoted_path(source_path)}'
+	res := os.execute(cmd)
+	assert res.exit_code == 0, '${cmd}\n${res.output}'
+}

vlib/v/gen/c/fn.v

@@ -12,6 +12,73 @@ import v.util
 // has[int, string]() => has_T_int_string()
 const c_fn_name_escape_seq = ['[', '_T_', ', ', '_', ']', '']
 
+// c_manual_prelude_decl_names matches the C stdlib declarations emitted by `c_headers`.
+// When one of these symbols is declared in V as `fn C.name(...)`, cgen must not emit an
+// extra fallback prototype, or it can conflict with the prelude declaration.
+const c_manual_prelude_decl_names = [
+	'vfprintf',
+	'vsnprintf',
+	'fprintf',
+	'printf',
+	'snprintf',
+	'sprintf',
+	'sscanf',
+	'scanf',
+	'puts',
+	'perror',
+	'fputs',
+	'getchar',
+	'putchar',
+	'getc',
+	'fgetc',
+	'ungetc',
+	'fflush',
+	'feof',
+	'ferror',
+	'clearerr',
+	'setvbuf',
+	'ftell',
+	'rewind',
+	'fopen',
+	'fdopen',
+	'freopen',
+	'fileno',
+	'fread',
+	'fwrite',
+	'fgets',
+	'fclose',
+	'popen',
+	'pclose',
+	'malloc',
+	'calloc',
+	'realloc',
+	'aligned_alloc',
+	'free',
+	'atexit',
+	'exit',
+	'atoi',
+	'getenv',
+	'setenv',
+	'unsetenv',
+	'system',
+	'remove',
+	'rename',
+	'realpath',
+	'qsort',
+	'strcmp',
+	'strlen',
+	'strerror',
+	'memcpy',
+	'memmove',
+	'memset',
+	'memcmp',
+	'memchr',
+	'strchr',
+	'strrchr',
+	'fseek',
+	'getline',
+]
+
 fn collect_function_defer_stmts(node &ast.FnDecl) []ast.DeferStmt {
 	mut defer_stmts := []ast.DeferStmt{}
 	mut seen_idxs := []int{}
@@ -736,9 +803,14 @@ fn (g &Gen) module_has_c_header_module(file &ast.File) bool {
 	return false
 }
 
+fn (g &Gen) c_prelude_provides_decl(c_sym_name string) bool {
+	return !g.pref.no_preludes && !g.pref.is_bare && c_sym_name in c_manual_prelude_decl_names
+}
+
 fn (g &Gen) should_emit_c_fallback_decl(node ast.FnDecl) bool {
+	c_sym_name := node.name.all_after_first('C__').all_after_first('C.')
 	if node.language != .c || node.is_c_extern || file_has_c_includes(node.source_file)
-		|| g.module_has_c_header_module(node.source_file) {
+		|| g.module_has_c_header_module(node.source_file) || g.c_prelude_provides_decl(c_sym_name) {
 		return false
 	}
 	if node.source_file == unsafe { nil } {