/*
 * Parse and validate C declarations.
 * Copyright © 2011-2012, 2020-2021, 2023-2024 Nick Bowler
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <config.h>
#include <stdio.h>
#include <assert.h>
#include <stdbool.h>

#include "cdecl.h"
#include "cdecl-internal.h"
#include "parse.h"
#include "scan.h"
#include "errmsg.h"

static struct cdecl *fake_function_param(struct cdecl_declarator *);

/*
 * Allocate a "parse item", which is a union of several parse tree
 * structure types, together with a string buffer.  The s_sz argument
 * specifies the size of the string (including its terminator), which
 * may be zero.
 *
 * The union's declarator member is pre-initialized to a valid "identifier"
 * declarator, which shares several interesting offsets with the "declspec"
 * structure for an "identifier" type specifier.
 */
struct parse_item *cdecl__alloc_item(size_t s_sz)
{
	struct parse_item *ret;

	ret = malloc(offsetof(struct parse_item, s) + s_sz);
	if (!ret) {
		cdecl__errmsg(CDECL__ENOMEM);
		return NULL;
	}

	ret->u.declarator.child   = NULL;
	ret->u.declarator.type    = CDECL_DECL_IDENT;
	ret->u.declarator.u.ident = ret->s;

	return ret;
}

/*
 * We can represent type specifiers as a bitmap, which gives us a finite
 * list of acceptable bitmap values according to the C standard.  However,
 * the "long" specifier is allowed to occur more than once, but only at most
 * 2 times.  Treat it as a special case, assigning an unused bit to represent
 * the second long.
 */
#define MAP_LLONG_BIT 31
#define MAP_LONG_BIT (CDECL_TYPE_LONG-CDECL_SPEC_TYPE)
#define CDECL_TYPE_LLONG (CDECL_SPEC_TYPE+MAP_LLONG_BIT)

#include "typemap.h"

/*
 * Convert the declaration specifiers to a bitmap with each bit
 * corresponding to one specific type specifier.
 */
static int valid_typespec(struct cdecl_declspec *s)
{
	struct cdecl_declspec *c;
	unsigned long map = 0;

	for (c = s; c; c = c->next) {
		unsigned long bit;

		if (cdecl_spec_kind(c) != CDECL_SPEC_TYPE)
			continue;

		bit = c->type - CDECL_SPEC_TYPE;
		assert(bit < MAP_LLONG_BIT);
		bit = 1ul << bit;

		/* "long" special case */
		if ((map & bit) == 1ul << MAP_LONG_BIT)
			bit = 1ul << MAP_LLONG_BIT;

		if (map & bit) {
			if (bit == 1ul << MAP_LLONG_BIT)
				cdecl__errmsg(CDECL__ETOOLONG);
			else
				cdecl__errmsg(CDECL__EDUPTYPE);
			return false;
		}
		map |= bit;
	}

	if (typemap_is_valid(map))
		return true;

	if (map == 0)
		cdecl__errmsg(CDECL__ENOTYPE);
	else
		cdecl__errmsg(CDECL__EBADTYPE);

	return false;
}

/*
 * Verify the declaration specifiers of a declaration.  If top is true, treat
 * this as a top-level declaration.  Otherwise, treat this as a function
 * parameter (which carries additional constraints).
 */
static bool valid_declspecs(struct cdecl *decl, bool top)
{
	struct cdecl_declspec *c, *specs = decl->specifiers;
	struct cdecl_declarator *d   = decl->declarators;
	bool abstract = cdecl_is_abstract(d);
	unsigned num_storage = 0;

	if (!valid_typespec(specs))
		return false;

	for (c = specs; c; c = c->next) {
		switch (cdecl_spec_kind(c)) {
		case CDECL_SPEC_TYPE:
			if (c->type == CDECL_TYPE_VOID &&
			    (d->type == CDECL_DECL_IDENT
		             || d->type == CDECL_DECL_ARRAY)) {
				cdecl__errmsg(CDECL__EBADVOID);
				return false;
			}
			continue;
		case CDECL_SPEC_STOR:
			if (top && abstract) {
				cdecl__errmsg(CDECL__ETYPESTOR);
				return false;
			}

			if (!top && c->type != CDECL_STOR_REGISTER) {
				cdecl__errmsg(CDECL__EFUNCSTOR);
				return false;
			}

			if (++num_storage > 1) {
				cdecl__errmsg(CDECL__EMANYSTOR);
				return false;
			}
			break;
		case CDECL_SPEC_QUAL:
			/*
			 * Restrict qualifiers are only valid in the
			 * pointer qualifier list, which isn't checked here.
			 */
			if (c->type == CDECL_QUAL_RESTRICT) {
				cdecl__errmsg(CDECL__EBADQUAL);
				return false;
			}
			break;
		case CDECL_SPEC_FUNC:
			if (abstract || !top || d->type != CDECL_DECL_FUNCTION) {
				cdecl__errmsg(CDECL__ENOTFUNC);
				return false;
			}

			break;
		default:
			assert(0);
		}
	}

	return true;
}

/*
 * Find the tree pointer which leads to the parameter's leaf node.
 *
 * Return a null pointer if the traversal locates a syntactic element which
 * prevents function reduction.  This occurs if the leaf node declares an
 * identifier, or for nontrivial fake function parameters (see below).
 */
static struct cdecl_declarator **leaf_pointer(struct cdecl *param)
{
	struct cdecl_declarator *d, **p = &param->declarators;

	if ((param = fake_function_param(param->declarators))) {
		if (param->declarators->type != CDECL_DECL_NULL)
			return NULL; /* e.g. int (x (*)) */
	}

	while ((d = *p)->child) {
		p = &d->child;

		if (fake_function_param(d->child))
			return NULL; /* e.g. int (x (*)[][1]) */
	}

	if (d->type != CDECL_DECL_NULL)
		return NULL; /* e.g. int (x y) */

	return p;
}


/*
 * The C grammar leaves ambiguous some cases where parentheses represent a
 * function declarator or just parentheses.  The language uses additional
 * context (whether or not a typedef is in scope, etc.) to resolve these
 * ambiguities, but we don't have access to that kind of information.
 *
 * The cdecl99 parser uses an unambiguous grammar which treats almost
 * everything as a function, and thus considers things like 'int (x)' to
 * be a function type with a single parameter of type 'x' (a typedef name),
 * returning int.  This can result in very complicated types for simple
 * declarations.  Ideally, cdecl99 should try and find the "simplest"
 * explanation for a given declaration.
 *
 * Whether or not it achieves the simplest explanation, we apply a simple rule:
 * if a declarator could be interpreted as something other than a function,
 * do that.
 *
 * Since cdecl99 supports things like [*] in any context (in C, such constructs
 * are only valid in function parameter lists), we don't treat them specially
 * here.
 */

static struct cdecl_declarator *reduce_function(struct cdecl *param)
{
	struct parse_item *spec = (void *)param->specifiers;
	struct cdecl_declarator *d, **p;

	if (!(p = leaf_pointer(param)))
		return NULL;

	/*
	 * The child and u.ident members of cdecl_declarator are expected
	 * to be located at identical offsets as, respectively, the next
	 * and ident members within cdecl_declspec, so the expectation is
	 * that the compiler can elide both assignments.
	 */
	spec->u.declarator.child = (void *)spec->u.declspec.next;
	spec->u.declarator.u.ident = spec->u.declspec.ident;
	spec->u.declarator.type = CDECL_DECL_IDENT;
	*p = &spec->u.declarator;

	d = param->declarators;
	free(param);
	return d;
}

static bool function_is_reducible(struct cdecl_declarator *d)
{
	if (d->type != CDECL_DECL_FUNCTION)
		return false;
	if (d->child->type != CDECL_DECL_NULL)
		return false; /* e.g., int (*)(x) */

	if (!d->u.function.parameters)
		return false; /* e.g., int f() */
	if (d->u.function.parameters->next)
		return false; /* e.g., int (x, y) */
	if (d->u.function.variadic)
		return false; /* e.g., int (x, ...) */

	if (d->u.function.parameters->specifiers->type != CDECL_TYPE_IDENT)
		return false; /* e.g. int (int) */
	if (d->u.function.parameters->specifiers->next)
		return false; /* e.g. int (size_t const) */
	if (d->u.function.parameters->declarators->type == CDECL_DECL_POINTER)
		return false; /* e.g. int (x *) */

	return true;
}

static int
simplify_functions(struct cdecl_declarator **p, struct cdecl_declarator *d)
{
	struct cdecl_declarator *new;

	if (!function_is_reducible(d))
		return 0;

	new = reduce_function(d->u.function.parameters);
	if (!new)
		return 0;
	*p = new;
	free(d);

	return 1;
}

/*
 * The main parser's bias towards considering things as functions whenever
 * possible makes nested parentheses tricky.  "(x)" is considered to be part
 * of a function declarator until simplify_functions converts it.  The problem
 * is that "(((x)))" is not valid as part of a function declarator, but it _is_
 * valid as either an identifier enclosed thrice in parentheses, or an abstract
 * function declarator enclosed twice in parentheses.
 *
 * To avoid ambiguities, the main parser actually returns a function declarator
 * for every pair of parentheses.  The ones we need to look at consist of a
 * single parameter with an empty specifier list (noting that every real
 * function parameter will have at least one type specifier).
 *
 * There are two cases:
 *
 *   - For (), the parser emits a parameter with a lone null declarator.
 *     This fake parameter simply gets deleted, leaving us with a normal
 *     function declarator with an empty identifier list.
 *
 *   - Otherwise, the parameter's outermost declarator is not null.  The
 *     function itself is deleted, replaced in the parse tree with the
 *     fake parameter's declarator.
 *
 * Repeating until there no fake parameters, this reduction transforms, for
 * example, "(((x)))" into "(x)", an abstract function declarator.  The result
 * is then subject to the function simplification step, which will turn "(x)"
 * into x (declaring an identifier).
 *
 * The whole process is repeated until no more changes are made to the parse
 * tree, or a syntax error is detected.
 */
static struct cdecl *fake_function_param(struct cdecl_declarator *d)
{
	struct cdecl *param;

	if (d->type != CDECL_DECL_FUNCTION)
		return NULL;

	param = d->u.function.parameters;
	if (!param || param->specifiers)
		return NULL;

	assert(!param->next);
	return param;
}

static int
reduce_parentheses(struct cdecl_declarator **p, struct cdecl_declarator *d)
{
	struct cdecl *param;

	do {
		d = *p;
		while ((param = fake_function_param(d))) {
			struct cdecl_declarator *decl = param->declarators;
			d->u.function.parameters = NULL;

			if (decl->type != CDECL_DECL_NULL) {
				if (d->child->type != CDECL_DECL_NULL) {
					/* Fake parameter on real function. */
					d->u.function.parameters = param;
					cdecl__errmsg(CDECL__EBADPARAM);
					return -1;
				}

				param->declarators = d;
				*p = d = decl;
			}

			cdecl__free(param);
		}
	} while (simplify_functions(p, d));

	return 0;
}

/*
 * Returns nonzero iff the given specifier list contains a specifier
 * of the indicated type.
 */
static int have_specifier(struct cdecl_declspec *s, unsigned type)
{
	for (; s; s = s->next)
		if (s->type == type)
			return 1;
	return 0;
}

/*
 * Check syntax restrictions on a function declarator's child declarator.
 * That is, "pointer to function", "array of function" and "function
 * returning function".
 *
 * Returns -1 if the declaration is invalid, or 0 otherwise.
 */
static int check_function_child(struct cdecl_declarator *d)
{
	struct cdecl_pointer *ptr;

	switch (d->type) {
	case CDECL_DECL_POINTER:
		ptr = &d->u.pointer;
		if (have_specifier(ptr->qualifiers, CDECL_QUAL_RESTRICT)) {
			/* pointer to function cannot be restrict qualified. */
			cdecl__errmsg(CDECL__ERESTRICTFUNC);
			return -1;
		}
		return 0;
	case CDECL_DECL_FUNCTION:
		/* function returning function is never allowed. */
		cdecl__errmsg(CDECL__ERETFUNC);
		return -1;
	case CDECL_DECL_ARRAY:
		/* array of function is never allowed. */
		cdecl__errmsg(CDECL__EFUNCARRAY);
		return -1;
	}

	return 0;
}

/*
 * Check a function parameter declaration for validity, which means it has a
 * valid combination of declaration specifiers and, if it is a void parameter,
 * that it is the one special case where this is allowed.
 *
 * Returns -1 if the declaration is invalid, or 0 otherwise.
 */
static int check_function_param(struct cdecl_function *f, struct cdecl *param)
{
	if (!valid_declspecs(param, false))
		return -1;

	/* Check for "void" function parameters as a special case. */
	if (param->declarators->type == CDECL_DECL_NULL
	    && have_specifier(param->specifiers, CDECL_TYPE_VOID))
	{
		struct cdecl *fp = f->parameters;

		if (f->variadic || fp->next || fp->specifiers->next) {
			cdecl__errmsg(CDECL__EVOIDPARAM);
			return -1;
		}
	}

	return 0;
}

/*
 * Normalize the specifier lists for function parameters, and then check the
 * function declarator for validity.
 *
 * Returns -1 if the declaration is invalid, or 0 otherwise.
 */
static int postproc_function(struct cdecl_declarator *d)
{
	struct cdecl_function *func = &d->u.function;
	struct cdecl *param;
	int rc;

	for (param = func->parameters; param; param = param->next) {
		param->specifiers = cdecl__normalize_specs(param->specifiers);

		if ((rc = check_function_param(func, param)) < 0)
			return rc;
	}

	return check_function_child(d->child);
}

static int
postproc_common(struct cdecl_declarator **p, struct cdecl_declarator *d)
{
	struct cdecl_pointer *ptr;

	switch (d->type) {
	case CDECL_DECL_POINTER:
		ptr = &d->u.pointer;
		ptr->qualifiers = cdecl__normalize_specs(ptr->qualifiers);
		return 0;
	case CDECL_DECL_FUNCTION:
		return postproc_function(d);
	case CDECL_DECL_ARRAY:
		if (d->child && d->child->type == CDECL_DECL_FUNCTION) {
			/* function returning array is never allowed. */
			cdecl__errmsg(CDECL__ERETARRAY);
			return -1;
		}
		return 0;
	}

	return 0;
}

/*
 * Traverse the parse tree, calling a function on every declarator in a
 * depth-first preorder traversal.  The function is given a pointer to the
 * declarator as well as to the pointer which was used to reach that
 * declarator: this can be used to rewrite entire subtrees.
 *
 * The called function may return a negative value to indicate an error
 * which terminates traversal.
 *
 * Returns 0 on success, or a negative value on failure.
 */
static int forall_declarators(struct cdecl *decl,
	int f(struct cdecl_declarator **, struct cdecl_declarator *))
{
	struct cdecl_declarator *d, **p;

	for (p = &decl->declarators; *p; p = &d->child) {
		int rc;

		rc = f(p, *p);
		if (rc < 0)
			return rc;
		d = *p;

		if (d->type == CDECL_DECL_FUNCTION) {
			struct cdecl *i;

			for (i = d->u.function.parameters; i; i = i->next) {
				rc = forall_declarators(i, f);
				if (rc < 0)
					return rc;
			}
		}
	}

	return 0;
}

static struct cdecl *do_parse(const char *str, int english_mode)
{
	struct cdecl *decl = NULL;
	YY_BUFFER_STATE state;
	yyscan_t scanner;

#if YYDEBUG
	extern int cdecl__yydebug;
	cdecl__yydebug = 1;
#endif

	cdecl__init_i18n();
	if (cdecl__yylex_init_extra(english_mode, &scanner) != 0)
		return NULL;

	state = cdecl__yy_scan_string(str, scanner);
	if (cdecl__yyparse(scanner, &decl) != 0) {
		/*
		 * If the input consists of a complete, valid declaration
		 * followed by some garbage, that parsed declaration will
		 * be output by the parser and we need to free it here.
		 */
		cdecl__free(decl);
		decl = NULL;
	}
	cdecl__yy_delete_buffer(state, scanner);
	cdecl__yylex_destroy(scanner);

	return decl;
}

static int do_postprocess(struct cdecl *decl, int english_mode)
{
	struct cdecl_declspec *norm_specs;
	struct cdecl *i;

	/*
	 * For a C declaration with more than one full declarator, the
	 * specifier list is common to all of them.  Normalize it once,
	 * then propagate that to all the linked cdecl structures.
	 *
	 * In english mode, the cdecl structure list always has exactly
	 * one entry so we don't need to do anything differently.
	 */
	norm_specs = cdecl__normalize_specs(decl->specifiers);
	for (i = decl; i; i = i->next)
		i->specifiers = norm_specs;

	for (i = decl; i; i = i->next) {
		if (!english_mode) {
			if (forall_declarators(i, reduce_parentheses) < 0)
				return 0;
		}

		if (forall_declarators(i, postproc_common) < 0)
			return 0;

		if (!valid_declspecs(i, true))
			return 0;

		if (decl->next && cdecl_is_abstract(i->declarators)) {
			/* Abstract full declarators: there can only be one. */
			cdecl__errmsg(CDECL__EDECLTYPE);
			return 0;
		}
	}

	return 1;
}

static struct cdecl *parse_common(const char *str, int english_mode)
{
	struct cdecl *decl;

	if (!(decl = do_parse(str, english_mode)))
		return NULL;

	if (!do_postprocess(decl, english_mode)) {
		cdecl__free(decl);
		return NULL;
	}

	return decl;
}

struct cdecl *cdecl_parse_decl(const char *declstr)
{
	return parse_common(declstr, false);
}

struct cdecl *cdecl_parse_english(const char *english)
{
	return parse_common(english, true);
}

void cdecl_free(struct cdecl *decl)
{
	cdecl__free(decl);
}