c++: Implement C++20 P1766R1 - Mitigating minor modules maladies [PR121552]

The following patch attempts to implement the
C++20 P1766R1 - Mitigating minor modules maladies
paper.
clang++ a few years ago introduced for the diagnostics required in
the paper -Wnon-c-typedef-for-linkage pedwarn and the following patch
does that too.
The paper was accepted as a DR, the patch enables the warning
also for C++98, dunno whether it might not be better to do it only
for C++11 onwards.

The paper is also about differences in default arguments of functions
in different TUs and in modules, I think within the same TU we diagnose
it correctly (maybe I should add some testcase) and perhaps try
something with modules as well.  But in different TUs it is IFNDR.

2025-08-15  Jakub Jelinek  <jakub@redhat.com>

	PR c++/121552
gcc/
	* doc/invoke.texi (-Wno-non-c-typedef-for-linkage): Document.
gcc/c-family/
	* c.opt (Wnon-c-typedef-for-linkage): New option.
	* c.opt.urls: Regenerate.
gcc/cp/
	* decl.cc: Implement C++20 P1766R1 - Mitigating minor modules maladies.
	(diagnose_non_c_class_typedef_for_linkage,
	maybe_diagnose_non_c_class_typedef_for_linkage): New functions.
	(name_unnamed_type): Call
	maybe_diagnose_non_c_class_typedef_for_linkage.
gcc/testsuite/
	* g++.dg/cpp2a/typedef1.C: New test.
	* g++.dg/debug/dwarf2/typedef5.C: Add -Wno-non-c-typedef-for-linkage
	to dg-options.
	* g++.dg/inherit/typeinfo1.C: Add -Wno-non-c-typedef-for-linkage
	to dg-additional-options.
	* g++.dg/parse/ctor2.C: Likewise.
	* g++.dg/ext/anon-struct9.C: Add -Wno-non-c-typedef-for-linkage to
	dg-options.
	* g++.dg/ext/visibility/anon11.C: Add -Wno-non-c-typedef-for-linkage
	to dg-additional-options.
	* g++.dg/lto/pr69137_0.C: Add -Wno-non-c-typedef-for-linkage
	to dg-lto-options.
	* g++.dg/other/anon8.C: Add -Wno-non-c-typedef-for-linkage
	to dg-additional-options.
	* g++.dg/template/pr84973.C: Likewise.
	* g++.dg/template/pr84973-2.C: Likewise.
	* g++.dg/template/pr84973-3.C: Likewise.
	* g++.dg/abi/anon2.C: Likewise.
	* g++.dg/abi/anon3.C: Likewise.
	* g++.old-deja/g++.oliva/linkage1.C: Likewise.

0 files changed, 0 insertions, 0 deletions