On 17/06/20 12:56 -0400, Jason Merrill wrote:
On 6/17/20 12:49 PM, Jonathan Wakely wrote:
On 17/06/20 12:32 -0400, Jason Merrill wrote:
On 6/15/20 3:40 PM, Jonathan Wakely wrote:
Ping ...
G++ gives a bogus warning for 'struct A; using B = struct ::A;'
complaining that the elaborated-type-specifier doesn't declare anything.
That's true, but it's not trying to declare struct ::A, just refer to it
unambiguously. Do not emit the warning unless we're actually parsing a
declaration.
This also makes the relevant warning depend on -Wredundant-decls (which
is not part of -Wall or -Wextra) so it can be disabled on the command
line or by using #pragma. This means the warning will no longer be given
by default, so some tests need -Wredundant-decls added.
gcc/cp/ChangeLog:
    PR c++/66159
    * parser.c (cp_parser_elaborated_type_specifier): Do not warn
    unless in a declaration. Make warning depend on
    WOPT_redundant_decls.
gcc/testsuite/ChangeLog:
    PR c++/66159
    * g++.dg/parse/specialization1.C: Remove dg-warning.
    * g++.dg/warn/forward-inner.C: Add -Wredundant-decls. Check
    alias-declaration using elaborated-type-specifier.
    * g++.dg/warn/pr36999.C: Add -Wredundant-decls.
Is it OK to make this warning no longer emitted by default, and not
even with -Wall -Wextra?
I'd like to keep it on by default.
Would it be better to add a new option for this specific warning,
which would be enabled by -Wall and also by -Wredundant-decls? Maybe
-Wredundant-decls-elaborated-type or something.
That sounds fine. But do you think people will really want to
turn this off after you fix the bug?
I don't know how to fix the bug, so I'll have to leave that to
somebody else.
By fixing the bug, I mean your "Do not emit the warning unless we're
actually parsing a declaration." Please do apply your change to the
condition for the warning.
Ah yes, I got confused about what the patch I eventually submitted
actually did, sorry!
I've pushed what's attached to this mail. Thanks.
commit d392babbeb6cb531ab8b1ec68fde9ffd36373a6e
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Wed Jun 17 20:26:13 2020 +0100
c++: Fix bogus "does not declare anything" warning (PR 66159)
G++ gives a bogus warning for 'struct A; using B = struct ::A;'
complaining that the elaborated-type-specifier doesn't declare anything.
That's true, but it's not trying to declare struct ::A, just refer to it
unambiguously. Do not emit the warning unless we're actually parsing a
declaration.
gcc/cp/ChangeLog:
PR c++/66159
* parser.c (cp_parser_elaborated_type_specifier): Do not warn
unless in a declaration.
gcc/testsuite/ChangeLog:
PR c++/66159
* g++.dg/warn/forward-inner.C: Check alias-declaration using
elaborated-type-specifier.
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 69839baa712..815582c825e 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -18953,7 +18953,8 @@ cp_parser_elaborated_type_specifier (cp_parser* parser,
here. */
if (cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON)
- && !is_friend && !processing_explicit_instantiation)
+ && !is_friend && is_declaration
+ && !processing_explicit_instantiation)
warning (0, "declaration %qD does not declare anything", decl);
type = TREE_TYPE (decl);
diff --git a/gcc/testsuite/g++.dg/warn/forward-inner.C b/gcc/testsuite/g++.dg/warn/forward-inner.C
index 5336d4ed946..d7b93f8ad08 100644
--- a/gcc/testsuite/g++.dg/warn/forward-inner.C
+++ b/gcc/testsuite/g++.dg/warn/forward-inner.C
@@ -70,7 +70,7 @@ template class TC6<int>::TC7; // Valid explicit instantiation, no warning
// Verify that friend declarations, also easy to confuse with forward
-// declrations, are similarly not warned about.
+// declarations, are similarly not warned about.
class C8 {
public:
class C9 { };
@@ -79,3 +79,10 @@ class C10 {
public:
friend class C8::C9; // Valid friend declaration, no warning
};
+
+#if __cplusplus >= 201103L
+// Verify that alias-declarations using an elaborated-type-specifier and
+// nested-name-specifier are not warned about (PR c++/66159).
+struct C11;
+using A1 = struct ::C11; // Valid alias-decl, no warning
+#endif
