2 * Parse and validate C declarations.
3 * Copyright © 2011 Nick Bowler
5 * This program is free software: you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation, either version 3 of the License, or
8 * (at your option) any later version.
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program. If not, see <http://www.gnu.org/licenses/>.
28 * Verify the declaration specifiers of a declaration. If top is true, treat
29 * this as a top-level declaration. Otherwise, treat this as a function
30 * parameter (which carries additional constraints).
32 static bool valid_declspecs(struct cdecl *decl, bool top)
34 struct cdecl_declspec *specs = decl->specifiers;
35 struct cdecl_declarator *d = decl->declarators;
36 unsigned num_storage = 0;
37 unsigned long typemap;
39 typemap = cdecl__build_typemap(specs);
43 for (struct cdecl_declspec *c = specs; c; c = c->next) {
44 switch (cdecl_spec_kind(c)) {
46 if (c->type == CDECL_TYPE_VOID &&
47 (d->type == CDECL_DECL_IDENT
48 || d->type == CDECL_DECL_ARRAY)) {
49 fprintf(stderr, "invalid declaration of type void\n");
54 if (!top && c->type != CDECL_STOR_REGISTER) {
55 fprintf(stderr, "function parameters may only have register storage\n");
59 if (++num_storage > 1) {
60 fprintf(stderr, "too many storage-class specifiers\n");
66 * Restrict qualifiers are only valid in the
67 * pointer qualifier list, which isn't checked here.
69 if (c->type == CDECL_QUAL_RESTRICT) {
70 fprintf(stderr, "only pointer types can be restrict-qualified.\n");
75 if (!top || d->type != CDECL_DECL_FUNCTION) {
76 fprintf(stderr, "only function declarations may have function specifiers.\n");
89 * The C grammar leaves ambiguous some cases where parentheses represent a
90 * function declarator or just parentheses. The language uses additional
91 * context (whether or not a typedef is in scope, etc.) to resolve these
92 * ambiguities, but we don't have access to that kind of information.
94 * The cdecl99 parser uses an unambiguous grammar which treats almost
95 * everything as a function, and thus considers things like 'int (x)' to
96 * be a function type with a single parameter of type 'x' (a typedef name),
97 * returning int. This can result in very complicated types for simple
98 * declarations. Ideally, cdecl99 should try and find the "simplest"
99 * explanation for a given declaration.
101 * Whether or not it achieves the simplest explanation, we apply a simple rule:
102 * if a declarator could be interpreted as something other than a function,
105 * - The function declarator has a null child declarator.
106 * - The function declarator has exactly one parameter, and is not variadic.
107 * - The function parameter has a type specifier, and it is a typedef name.
108 * - The function parameter has no other declaration specifiers.
109 * - The function parameter does not declare an identifier.
111 * Since cdecl99 supports things like [*] in any context (in C, such constructs
112 * are only valid in function parameter lists), we don't treat them specially
116 static struct cdecl_declarator *reduce_function(struct cdecl *param)
118 struct cdecl_declspec *spec = param->specifiers;
119 struct cdecl_declarator *decl = param->declarators;
120 struct cdecl_declarator *last;
122 for (last = decl; last && last->type != CDECL_DECL_NULL;)
128 last->type = CDECL_DECL_IDENT;
129 last->u.ident = spec->ident;
136 static bool function_is_reducible(struct cdecl_declarator *d)
138 if (d->type != CDECL_DECL_FUNCTION)
140 if (d->child->type != CDECL_DECL_NULL)
141 return false; /* e.g., int (*)(x) */
143 if (!d->u.function.parameters)
144 return false; /* e.g., int f() */
145 if (d->u.function.parameters->next)
146 return false; /* e.g., int (x, y) */
147 if (d->u.function.variadic)
148 return false; /* e.g., int (x, ...) */
150 if (d->u.function.parameters->specifiers->type != CDECL_TYPE_IDENT)
151 return false; /* e.g. int (int) */
152 if (d->u.function.parameters->specifiers->next)
153 return false; /* e.g. int (size_t const) */
159 simplify_functions(struct cdecl_declarator **p, struct cdecl_declarator *d)
161 struct cdecl_declarator *new;
163 if (!function_is_reducible(d))
166 new = reduce_function(d->u.function.parameters);
168 return 0; /* e.g. int (foo bar) */
177 * The parser's bias towards considering things as functions whenever possible
178 * makes nested parentheses tricky. (x) is considered to be part of a function
179 * declarator until simplify_functions converts it. The problem is that
180 * (((x))) is not valid as part of a function declarator, but it *is* valid
181 * as an identifier enclosed 3 times in parentheses. This is complicated by
182 * the fact that things like (((int))) are not valid anywhere.
184 * To avoid ambiguities, the parser actually emits a "function" declarator for
185 * every pair of parentheses. The ones that can't reasonably be functions
186 * consist of a single "parameter" with no declaration specifiers (note that
187 * every valid function parameter will have at least one type specifier).
189 * This pass is to remove these fake functions from the parse tree. We take
190 * care to avoid turning invalid things like ((int)) into valid things like
191 * (int) by observing that the only valid function declarators that appear
192 * in these "fake" parentheses are those that have a non-null child declarator
193 * (for instance, int ((*)(int)) *or* those that will be eliminated by the
194 * simplify_functions pass.
198 reduce_parentheses(struct cdecl_declarator **p, struct cdecl_declarator *d)
202 if (d->type != CDECL_DECL_FUNCTION)
205 param = d->u.function.parameters;
206 if (param && param->specifiers == NULL) {
207 struct cdecl_declarator *decl;
209 assert(!param->next);
211 decl = param->declarators;
212 if (decl->type == CDECL_DECL_NULL) {
215 d->u.function.parameters = NULL;
219 if (d->child->type != CDECL_DECL_NULL) {
220 fprintf(stderr, "invalid function parameter\n");
230 * We may have replaced d with another fake function which
231 * also needs to be eliminated.
233 if (reduce_parentheses(p, decl) < 0)
237 * If the remaining declarator is a function, make sure it's
238 * valid by checking its reducibility.
241 if (decl->type == CDECL_DECL_FUNCTION
242 && decl->child->type == CDECL_DECL_NULL
243 && !function_is_reducible(decl)) {
244 fprintf(stderr, "too many parentheses in function\n");
255 check_parameters(struct cdecl_declarator **p, struct cdecl_declarator *d)
257 struct cdecl_declspec *spec;
259 bool has_void = false;
261 if (d->type != CDECL_DECL_FUNCTION)
264 for (param = d->u.function.parameters; param; param = param->next) {
265 if (!valid_declspecs(param, false))
268 for (spec = param->specifiers; spec; spec = spec->next) {
269 if (spec->type == CDECL_TYPE_VOID
270 && param->declarators->type == CDECL_DECL_NULL)
275 if (has_void && d->u.function.parameters->next) {
276 fprintf(stderr, "a void parameter must stand alone\n");
278 } else if (has_void && d->u.function.variadic) {
279 fprintf(stderr, "variadic functions cannot have a void parameter\n");
287 * Traverse the parse tree, calling a function on every declarator in a
288 * depth-first preorder traversal. The function is given a pointer to the
289 * declarator as well as to the pointer which was used to reach that
290 * declarator: this can be used to rewrite entire subtrees.
292 static bool forall_declarators(struct cdecl *decl,
293 int f(struct cdecl_declarator **, struct cdecl_declarator *))
295 struct cdecl_declarator *d, **p;
297 for (p = &decl->declarators, d = *p; d; p = &d->child, d = *p) {
310 if (d->type == CDECL_DECL_FUNCTION) {
313 for (i = d->u.function.parameters; i; i = i->next) {
314 if (!forall_declarators(i, f))
323 struct cdecl *cdecl_parse_decl(const char *declstr)
325 YY_BUFFER_STATE state;
329 state = yy_scan_string(declstr);
331 yy_delete_buffer(state);
336 for (struct cdecl *i = decl; i; i = i->next) {
337 if (!forall_declarators(i, reduce_parentheses))
339 if (!forall_declarators(i, simplify_functions))
341 if (!forall_declarators(i, check_parameters))
344 if (!valid_declspecs(i, true))