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c: Diagnose "enum tag;" after definition [PR107164]

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As noted in bug 101764, a declaration "enum tag;" is invalid in
standard C after a definition, as well as when no definition is
visible; we had a pedwarn-if-pedantic for the forward declaration
case, but were missing one for the other case.  Add that missing
diagnostic (if pedantic only).

(These diagnostics will need to be appropriately conditioned when
support is added for C2x enums with fixed underlying type, since "enum
tag : type;" is OK both before and after a definition.)

Bootstrapped with no regressions for x86_64-pc-linux-gnu.

	PR c/107164

gcc/c/
	* c-decl.cc (shadow_tag_warned): If pedantic, diagnose "enum tag;"
	with previous declaration visible.

gcc/testsuite/
	* gcc.dg/c99-tag-4.c, gcc.dg/c99-tag-5.c, gcc.dg/c99-tag-6.c: New
	tests.
This commit is contained in:
Joseph Myers 2022-10-18 23:25:47 +00:00
parent cc694f4508
commit f5f1d92fe2
4 changed files with 39 additions and 0 deletions
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14
gcc/c/c-decl.cc
View file

@ -4814,6 +4814,20 @@ shadow_tag_warned (const struct c_declspecs *declspecs, int warned)
warned = 1;
pending_xref_error ();
}
else if (declspecs->typespec_kind != ctsk_tagdef
&& declspecs->typespec_kind != ctsk_tagfirstref
&& declspecs->typespec_kind != ctsk_tagfirstref_attrs
&& code == ENUMERAL_TYPE)
{
bool warned_enum = false;
if (warned != 1)
warned_enum = pedwarn (input_location, OPT_Wpedantic,
"empty declaration of %<enum%> type "
"does not redeclare tag");
if (warned_enum)
warned = 1;
pending_xref_error ();
}
else
{
pending_invalid_xref = NULL_TREE;

8
gcc/testsuite/gcc.dg/c99-tag-4.c Normal file
View file

@ -0,0 +1,8 @@
/* Test for handling of tags. "enum foo;" is invalid after an existing
declaration (does not redeclare the tag) as well as before: bug 107164. */
/* { dg-do compile } */
/* { dg-options "-std=c99 -pedantic-errors" } */
enum e1; /* { dg-error "ISO C forbids forward references to 'enum' types" } */
enum e2 { E };
enum e2; /* { dg-error "empty declaration of 'enum' type does not redeclare tag" } */

8
gcc/testsuite/gcc.dg/c99-tag-5.c Normal file
View file

@ -0,0 +1,8 @@
/* Test for handling of tags. "enum foo;" is invalid after an existing
declaration (does not redeclare the tag) as well as before: bug 107164. */
/* { dg-do compile } */
/* { dg-options "-std=c99 -pedantic" } */
enum e1; /* { dg-warning "ISO C forbids forward references to 'enum' types" } */
enum e2 { E };
enum e2; /* { dg-warning "empty declaration of 'enum' type does not redeclare tag" } */

9
gcc/testsuite/gcc.dg/c99-tag-6.c Normal file
View file

@ -0,0 +1,9 @@
/* Test for handling of tags. "enum foo;" is invalid after an existing
declaration (does not redeclare the tag) as well as before: bug 107164.
Test this is not diagnosed without -pedantic. */
/* { dg-do compile } */
/* { dg-options "-std=c99" } */
enum e1;
enum e2 { E };
enum e2;