2 * Parse and validate C declarations.
3 * Copyright © 2011-2012, 2020-2021, 2023-2024 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 <https://www.gnu.org/licenses/>.
25 #include "cdecl-internal.h"
30 static struct cdecl *fake_function_param(struct cdecl_declarator *);
33 * Allocate a "parse item", which is a union of several parse tree
34 * structure types, together with a string buffer. The s_sz argument
35 * specifies the size of the string (including its terminator), which
38 * The union's declarator member is pre-initialized to a valid "identifier"
39 * declarator, which shares several interesting offsets with the "declspec"
40 * structure for an "identifier" type specifier.
42 struct parse_item *cdecl__alloc_item(size_t s_sz)
44 struct parse_item *ret;
46 ret = malloc(offsetof(struct parse_item, s) + s_sz);
48 cdecl__errmsg(CDECL__ENOMEM);
52 ret->u.declarator.child = NULL;
53 ret->u.declarator.type = CDECL_DECL_IDENT;
54 ret->u.declarator.u.ident = ret->s;
60 * We can represent type specifiers as a bitmap, which gives us a finite
61 * list of acceptable bitmap values according to the C standard. However,
62 * the "long" specifier is allowed to occur more than once, but only at most
63 * 2 times. Treat it as a special case, assigning an unused bit to represent
66 #define MAP_LLONG_BIT 31
67 #define MAP_LONG_BIT (CDECL_TYPE_LONG-CDECL_SPEC_TYPE)
68 #define CDECL_TYPE_LLONG (CDECL_SPEC_TYPE+MAP_LLONG_BIT)
73 * Convert the declaration specifiers to a bitmap with each bit
74 * corresponding to one specific type specifier.
76 static int valid_typespec(struct cdecl_declspec *s)
78 struct cdecl_declspec *c;
79 unsigned long map = 0;
81 for (c = s; c; c = c->next) {
84 if (cdecl_spec_kind(c) != CDECL_SPEC_TYPE)
87 bit = c->type - CDECL_SPEC_TYPE;
88 assert(bit < MAP_LLONG_BIT);
91 /* "long" special case */
92 if ((map & bit) == 1ul << MAP_LONG_BIT)
93 bit = 1ul << MAP_LLONG_BIT;
96 if (bit == 1ul << MAP_LLONG_BIT)
97 cdecl__errmsg(CDECL__ETOOLONG);
99 cdecl__errmsg(CDECL__EDUPTYPE);
105 if (typemap_is_valid(map))
109 cdecl__errmsg(CDECL__ENOTYPE);
111 cdecl__errmsg(CDECL__EBADTYPE);
117 * Verify the declaration specifiers of a declaration. If top is true, treat
118 * this as a top-level declaration. Otherwise, treat this as a function
119 * parameter (which carries additional constraints).
121 static bool valid_declspecs(struct cdecl *decl, bool top)
123 struct cdecl_declspec *c, *specs = decl->specifiers;
124 struct cdecl_declarator *d = decl->declarators;
125 bool abstract = cdecl_is_abstract(d);
126 unsigned num_storage = 0;
128 if (!valid_typespec(specs))
131 for (c = specs; c; c = c->next) {
132 switch (cdecl_spec_kind(c)) {
133 case CDECL_SPEC_TYPE:
134 if (c->type == CDECL_TYPE_VOID &&
135 (d->type == CDECL_DECL_IDENT
136 || d->type == CDECL_DECL_ARRAY)) {
137 cdecl__errmsg(CDECL__EBADVOID);
141 case CDECL_SPEC_STOR:
142 if (top && abstract) {
143 cdecl__errmsg(CDECL__ETYPESTOR);
147 if (!top && c->type != CDECL_STOR_REGISTER) {
148 cdecl__errmsg(CDECL__EFUNCSTOR);
152 if (++num_storage > 1) {
153 cdecl__errmsg(CDECL__EMANYSTOR);
157 case CDECL_SPEC_QUAL:
159 * Restrict qualifiers are only valid in the
160 * pointer qualifier list, which isn't checked here.
162 if (c->type == CDECL_QUAL_RESTRICT) {
163 cdecl__errmsg(CDECL__EBADQUAL);
167 case CDECL_SPEC_FUNC:
168 if (abstract || !top || d->type != CDECL_DECL_FUNCTION) {
169 cdecl__errmsg(CDECL__ENOTFUNC);
183 * Find the tree pointer which leads to the parameter's leaf node.
185 * Return a null pointer if the traversal locates a syntactic element which
186 * prevents function reduction. This occurs if the leaf node declares an
187 * identifier, or for nontrivial fake function parameters (see below).
189 static struct cdecl_declarator **leaf_pointer(struct cdecl *param)
191 struct cdecl_declarator *d, **p = ¶m->declarators;
193 if ((param = fake_function_param(param->declarators))) {
194 if (param->declarators->type != CDECL_DECL_NULL)
195 return NULL; /* e.g. int (x (*)) */
198 while ((d = *p)->child) {
201 if (fake_function_param(d->child))
202 return NULL; /* e.g. int (x (*)[][1]) */
205 if (d->type != CDECL_DECL_NULL)
206 return NULL; /* e.g. int (x y) */
213 * The C grammar leaves ambiguous some cases where parentheses represent a
214 * function declarator or just parentheses. The language uses additional
215 * context (whether or not a typedef is in scope, etc.) to resolve these
216 * ambiguities, but we don't have access to that kind of information.
218 * The cdecl99 parser uses an unambiguous grammar which treats almost
219 * everything as a function, and thus considers things like 'int (x)' to
220 * be a function type with a single parameter of type 'x' (a typedef name),
221 * returning int. This can result in very complicated types for simple
222 * declarations. Ideally, cdecl99 should try and find the "simplest"
223 * explanation for a given declaration.
225 * Whether or not it achieves the simplest explanation, we apply a simple rule:
226 * if a declarator could be interpreted as something other than a function,
229 * Since cdecl99 supports things like [*] in any context (in C, such constructs
230 * are only valid in function parameter lists), we don't treat them specially
234 static struct cdecl_declarator *reduce_function(struct cdecl *param)
236 struct parse_item *spec = (void *)param->specifiers;
237 struct cdecl_declarator *d, **p;
239 if (!(p = leaf_pointer(param)))
243 * The child and u.ident members of cdecl_declarator are expected
244 * to be located at identical offsets as, respectively, the next
245 * and ident members within cdecl_declspec, so the expectation is
246 * that the compiler can elide both assignments.
248 spec->u.declarator.child = (void *)spec->u.declspec.next;
249 spec->u.declarator.u.ident = spec->u.declspec.ident;
250 spec->u.declarator.type = CDECL_DECL_IDENT;
251 *p = &spec->u.declarator;
253 d = param->declarators;
258 static bool function_is_reducible(struct cdecl_declarator *d)
260 if (d->type != CDECL_DECL_FUNCTION)
262 if (d->child->type != CDECL_DECL_NULL)
263 return false; /* e.g., int (*)(x) */
265 if (!d->u.function.parameters)
266 return false; /* e.g., int f() */
267 if (d->u.function.parameters->next)
268 return false; /* e.g., int (x, y) */
269 if (d->u.function.variadic)
270 return false; /* e.g., int (x, ...) */
272 if (d->u.function.parameters->specifiers->type != CDECL_TYPE_IDENT)
273 return false; /* e.g. int (int) */
274 if (d->u.function.parameters->specifiers->next)
275 return false; /* e.g. int (size_t const) */
276 if (d->u.function.parameters->declarators->type == CDECL_DECL_POINTER)
277 return false; /* e.g. int (x *) */
283 simplify_functions(struct cdecl_declarator **p, struct cdecl_declarator *d)
285 struct cdecl_declarator *new;
287 if (!function_is_reducible(d))
290 new = reduce_function(d->u.function.parameters);
300 * The main parser's bias towards considering things as functions whenever
301 * possible makes nested parentheses tricky. "(x)" is considered to be part
302 * of a function declarator until simplify_functions converts it. The problem
303 * is that "(((x)))" is not valid as part of a function declarator, but it _is_
304 * valid as either an identifier enclosed thrice in parentheses, or an abstract
305 * function declarator enclosed twice in parentheses.
307 * To avoid ambiguities, the main parser actually returns a function declarator
308 * for every pair of parentheses. The ones we need to look at consist of a
309 * single parameter with an empty specifier list (noting that every real
310 * function parameter will have at least one type specifier).
312 * There are two cases:
314 * - For (), the parser emits a parameter with a lone null declarator.
315 * This fake parameter simply gets deleted, leaving us with a normal
316 * function declarator with an empty identifier list.
318 * - Otherwise, the parameter's outermost declarator is not null. The
319 * function itself is deleted, replaced in the parse tree with the
320 * fake parameter's declarator.
322 * Repeating until there no fake parameters, this reduction transforms, for
323 * example, "(((x)))" into "(x)", an abstract function declarator. The result
324 * is then subject to the function simplification step, which will turn "(x)"
325 * into x (declaring an identifier).
327 * The whole process is repeated until no more changes are made to the parse
328 * tree, or a syntax error is detected.
330 static struct cdecl *fake_function_param(struct cdecl_declarator *d)
334 if (d->type != CDECL_DECL_FUNCTION)
337 param = d->u.function.parameters;
338 if (!param || param->specifiers)
341 assert(!param->next);
346 reduce_parentheses(struct cdecl_declarator **p, struct cdecl_declarator *d)
352 while ((param = fake_function_param(d))) {
353 struct cdecl_declarator *decl = param->declarators;
354 d->u.function.parameters = NULL;
356 if (decl->type != CDECL_DECL_NULL) {
357 if (d->child->type != CDECL_DECL_NULL) {
358 /* Fake parameter on real function. */
359 d->u.function.parameters = param;
360 cdecl__errmsg(CDECL__EBADPARAM);
364 param->declarators = d;
370 } while (simplify_functions(p, d));
376 * Returns nonzero iff the given specifier list contains a specifier
377 * of the indicated type.
379 static int have_specifier(struct cdecl_declspec *s, unsigned type)
381 for (; s; s = s->next)
388 * Check syntax restrictions on a function declarator's child declarator.
389 * That is, "pointer to function", "array of function" and "function
390 * returning function".
392 * Returns -1 if the declaration is invalid, or 0 otherwise.
394 static int check_function_child(struct cdecl_declarator *d)
396 struct cdecl_pointer *ptr;
399 case CDECL_DECL_POINTER:
401 if (have_specifier(ptr->qualifiers, CDECL_QUAL_RESTRICT)) {
402 /* pointer to function cannot be restrict qualified. */
403 cdecl__errmsg(CDECL__ERESTRICTFUNC);
407 case CDECL_DECL_FUNCTION:
408 /* function returning function is never allowed. */
409 cdecl__errmsg(CDECL__ERETFUNC);
411 case CDECL_DECL_ARRAY:
412 /* array of function is never allowed. */
413 cdecl__errmsg(CDECL__EFUNCARRAY);
421 * Check a function parameter declaration for validity, which means it has a
422 * valid combination of declaration specifiers and, if it is a void parameter,
423 * that it is the one special case where this is allowed.
425 * Returns -1 if the declaration is invalid, or 0 otherwise.
427 static int check_function_param(struct cdecl_function *f, struct cdecl *param)
429 if (!valid_declspecs(param, false))
432 /* Check for "void" function parameters as a special case. */
433 if (param->declarators->type == CDECL_DECL_NULL
434 && have_specifier(param->specifiers, CDECL_TYPE_VOID))
436 struct cdecl *fp = f->parameters;
438 if (f->variadic || fp->next || fp->specifiers->next) {
439 cdecl__errmsg(CDECL__EVOIDPARAM);
448 * Normalize the specifier lists for function parameters, and then check the
449 * function declarator for validity.
451 * Returns -1 if the declaration is invalid, or 0 otherwise.
453 static int postproc_function(struct cdecl_declarator *d)
455 struct cdecl_function *func = &d->u.function;
459 for (param = func->parameters; param; param = param->next) {
460 param->specifiers = cdecl__normalize_specs(param->specifiers);
462 if ((rc = check_function_param(func, param)) < 0)
466 return check_function_child(d->child);
470 postproc_common(struct cdecl_declarator **p, struct cdecl_declarator *d)
472 struct cdecl_pointer *ptr;
475 case CDECL_DECL_POINTER:
477 ptr->qualifiers = cdecl__normalize_specs(ptr->qualifiers);
479 case CDECL_DECL_FUNCTION:
480 return postproc_function(d);
481 case CDECL_DECL_ARRAY:
482 if (d->child && d->child->type == CDECL_DECL_FUNCTION) {
483 /* function returning array is never allowed. */
484 cdecl__errmsg(CDECL__ERETARRAY);
494 * Traverse the parse tree, calling a function on every declarator in a
495 * depth-first preorder traversal. The function is given a pointer to the
496 * declarator as well as to the pointer which was used to reach that
497 * declarator: this can be used to rewrite entire subtrees.
499 * The called function may return a negative value to indicate an error
500 * which terminates traversal.
502 * Returns 0 on success, or a negative value on failure.
504 static int forall_declarators(struct cdecl *decl,
505 int f(struct cdecl_declarator **, struct cdecl_declarator *))
507 struct cdecl_declarator *d, **p;
509 for (p = &decl->declarators; *p; p = &d->child) {
517 if (d->type == CDECL_DECL_FUNCTION) {
520 for (i = d->u.function.parameters; i; i = i->next) {
521 rc = forall_declarators(i, f);
531 static struct cdecl *do_parse(const char *str, int english_mode)
533 struct cdecl *decl = NULL;
534 YY_BUFFER_STATE state;
538 extern int cdecl__yydebug;
543 if (cdecl__yylex_init_extra(english_mode, &scanner) != 0)
546 state = cdecl__yy_scan_string(str, scanner);
547 if (cdecl__yyparse(scanner, &decl) != 0) {
549 * If the input consists of a complete, valid declaration
550 * followed by some garbage, that parsed declaration will
551 * be output by the parser and we need to free it here.
556 cdecl__yy_delete_buffer(state, scanner);
557 cdecl__yylex_destroy(scanner);
562 static int do_postprocess(struct cdecl *decl, int english_mode)
564 struct cdecl_declspec *norm_specs;
568 * For a C declaration with more than one full declarator, the
569 * specifier list is common to all of them. Normalize it once,
570 * then propagate that to all the linked cdecl structures.
572 * In english mode, the cdecl structure list always has exactly
573 * one entry so we don't need to do anything differently.
575 norm_specs = cdecl__normalize_specs(decl->specifiers);
576 for (i = decl; i; i = i->next)
577 i->specifiers = norm_specs;
579 for (i = decl; i; i = i->next) {
581 if (forall_declarators(i, reduce_parentheses) < 0)
585 if (forall_declarators(i, postproc_common) < 0)
588 if (!valid_declspecs(i, true))
591 if (decl->next && cdecl_is_abstract(i->declarators)) {
592 /* Abstract full declarators: there can only be one. */
593 cdecl__errmsg(CDECL__EDECLTYPE);
601 static struct cdecl *parse_common(const char *str, int english_mode)
605 if (!(decl = do_parse(str, english_mode)))
608 if (!do_postprocess(decl, english_mode)) {
616 struct cdecl *cdecl_parse_decl(const char *declstr)
618 return parse_common(declstr, false);
621 struct cdecl *cdecl_parse_english(const char *english)
623 return parse_common(english, true);
626 void cdecl_free(struct cdecl *decl)