[PATCH 59/73] c23: Treat empty parameter list () as (void) and reject K&R functions

[Bart Van Assche <bvanassche@acm.org>]

Treat an empty parameter list '()' in a function declarator as '(void)'
and reject K&R identifier-list function declarations and definitions in
C23 mode per ISO C23 6.7.6.3 and 6.9.1:
- Parse '()' as a zero-parameter prototype in C23 mode so calls with
  arguments and conflicting redeclarations are diagnosed.
- Track identifier-list declarators via kr_args on SYM_FN and report an
  error in C23 mode on K&R function definitions (with or without
  parameter declarations) and K&R function or function-pointer
  declarations.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 parse.c                             | 34 ++++++++++++++++++---
 symbol.h                            |  1 +
 validation/c23-empty-parameters.c   | 29 ++++++++++++++++++
 validation/c23-empty-params-error.c | 47 +++++++++++++++++++++++++++++
 validation/c23-knr-error.c          | 14 +++++++++
 5 files changed, 120 insertions(+), 5 deletions(-)
 create mode 100644 validation/c23-empty-parameters.c
 create mode 100644 validation/c23-empty-params-error.c
 create mode 100644 validation/c23-knr-error.c

diff --git a/parse.c b/parse.c
index f49b3f188c69..782683a84fba 100644
--- a/parse.c
+++ b/parse.c
@@ -2241,9 +2241,14 @@ static enum kind which_func(struct token *token,
 		if (lookup_type(next) || next != token->next)
 			return Proto;
 		/* identifier list not in definition; complain */
-		if (prefer_abstract)
-			warning(token->pos,
-				"identifier list not in definition");
+		if (prefer_abstract || !n) {
+			if (standard >= STANDARD_C23)
+				sparse_error(token->pos,
+					     "identifier list not in definition");
+			else
+				warning(token->pos,
+					"identifier list not in definition");
+		}
 		return K_R;
 	}
 
@@ -2251,6 +2256,8 @@ static enum kind which_func(struct token *token,
 		return Bad_Func;
 
 	if (next->special == ')') {
+		if (standard >= STANDARD_C23)
+			return Proto;
 		/* don't complain about those */
 		if (!n || match_op(next->next, ';') || match_op(next->next, ','))
 			return Empty;
@@ -3284,6 +3291,7 @@ static struct token * statement_list(struct token *token, struct statement_list
 static struct token *identifier_list(struct token *token, struct symbol *fn)
 {
 	struct symbol_list **list = &fn->arguments;
+	fn->kr_args = 1;
 	for (;;) {
 		struct symbol *sym = alloc_symbol(token->pos, SYM_NODE);
 		sym->ident = token->ident;
@@ -3304,6 +3312,9 @@ static struct token *parameter_type_list(struct token *token, struct symbol *fn)
 {
 	struct symbol_list **list = &fn->arguments;
 
+	if (match_op(token, ')'))
+		return token;
+
 	for (;;) {
 		struct symbol *sym;
 
@@ -3602,7 +3613,10 @@ static struct token *parse_k_r_arguments(struct token *token, struct symbol *dec
 {
 	struct symbol_list *args = NULL;
 
-	if (Wold_style_definition)
+	if (standard >= STANDARD_C23)
+		sparse_error(token->pos,
+			     "old-style function definition is invalid in C23");
+	else if (Wold_style_definition)
 		warning(token->pos, "non-ANSI definition of function '%s'", show_ident(decl->ident));
 
 	do {
@@ -3772,8 +3786,15 @@ struct token *external_declaration(struct token *token, struct symbol_list **lis
 		}
 		if (lookup_type(token))
 			return parse_k_r_arguments(token, decl, list);
-		if (match_op(token, '{'))
+		if (match_op(token, '{')) {
+			if (standard >= STANDARD_C23 && base_type->kr_args)
+				sparse_error(decl->pos,
+					     "old-style function definition is invalid in C23");
 			return parse_function_body(token, decl, list);
+		}
+		if (standard >= STANDARD_C23 && base_type->kr_args)
+			sparse_error(decl->pos,
+				     "identifier list not in function definition");
 
 		if (!(decl->ctype.modifiers & MOD_STATIC))
 			decl->ctype.modifiers |= MOD_EXTERN;
@@ -3977,6 +3998,9 @@ struct token *external_declaration(struct token *token, struct symbol_list **lis
 		base_type = decl->ctype.base_type;
 		if (!is_typedef && base_type && base_type->type == SYM_FN) {
 			decl->ctype.modifiers |= ctx.f_modifiers;
+			if (standard >= STANDARD_C23 && base_type->kr_args)
+				sparse_error(decl->pos,
+					     "identifier list not in function definition");
 			if (!(decl->ctype.modifiers & MOD_STATIC))
 				decl->ctype.modifiers |= MOD_EXTERN;
 		}
diff --git a/symbol.h b/symbol.h
index a072ac8fc739..942baad97df5 100644
--- a/symbol.h
+++ b/symbol.h
@@ -198,6 +198,7 @@ struct symbol {
 				packed : 1, transparent_union : 1,
 				fixed_type : 1;
 			unsigned int has_alignas : 1;
+			unsigned int kr_args : 1;
 			unsigned int underspecified : 1;
 			unsigned int c23_auto : 1;
 			int		rank:3;	// arithmetic's rank
diff --git a/validation/c23-empty-parameters.c b/validation/c23-empty-parameters.c
new file mode 100644
index 000000000000..9c493256d54b
--- /dev/null
+++ b/validation/c23-empty-parameters.c
@@ -0,0 +1,29 @@
+int f();
+int f(void)
+{
+	return 0;
+}
+
+int g(void);
+int g()
+{
+	return 1;
+}
+
+static int h()
+{
+	return 2;
+}
+
+static int test(void)
+{
+	int (*fp)() = f;
+	int (*fp2)(void) = h;
+
+	return fp() + fp2() + g();
+}
+
+/*
+ * check-name: c23-empty-parameters
+ * check-command: sparse -std=c23 -Wstrict-prototypes -pedantic $file
+ */
diff --git a/validation/c23-empty-params-error.c b/validation/c23-empty-params-error.c
new file mode 100644
index 000000000000..4c0efe972358
--- /dev/null
+++ b/validation/c23-empty-params-error.c
@@ -0,0 +1,47 @@
+int f();
+
+static int h()
+{
+	return 0;
+}
+
+int mismatch();
+int mismatch(int x)
+{
+	return x;
+}
+
+int ident_decl(a, b);
+int (*bad_fp)(a, b);
+
+int old_implicit(a, b)
+{
+	return 0;
+}
+
+static void bad_calls(int (*fp)())
+{
+	f(1);
+	h(1, 2);
+	fp(3);
+}
+
+/*
+ * check-name: c23-empty-params-error
+ * check-command: sparse -std=c23 -Wno-decl $file
+ *
+ * check-error-start
+c23-empty-params-error.c:14:5: error: identifier list not in function definition
+c23-empty-params-error.c:15:14: error: identifier list not in definition
+c23-empty-params-error.c:17:5: error: old-style function definition is invalid in C23
+c23-empty-params-error.c:17:18: error: missing type declaration for parameter 'a'
+c23-empty-params-error.c:17:21: error: missing type declaration for parameter 'b'
+c23-empty-params-error.c:9:5: error: symbol 'mismatch' redeclared with different type (different argument counts):
+c23-empty-params-error.c:9:5:    int extern [addressable] [signed] [toplevel] mismatch( ... )
+c23-empty-params-error.c:8:5: note: previously declared as:
+c23-empty-params-error.c:8:5:    int extern [addressable] [signed] [toplevel] mismatch( ... )
+c23-empty-params-error.c:24:10: error: too many arguments for function f
+c23-empty-params-error.c:25:10: error: too many arguments for function h
+c23-empty-params-error.c:26:11: error: too many arguments for function fp
+ * check-error-end
+ */
diff --git a/validation/c23-knr-error.c b/validation/c23-knr-error.c
new file mode 100644
index 000000000000..f7ae837815b5
--- /dev/null
+++ b/validation/c23-knr-error.c
@@ -0,0 +1,14 @@
+int old_func(a, b)
+int a, b;
+{
+	return a + b;
+}
+
+/*
+ * check-name: c23-knr-error
+ * check-command: sparse -std=c23 $file
+ *
+ * check-error-start
+c23-knr-error.c:2:1: error: old-style function definition is invalid in C23
+ * check-error-end
+ */