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c++: Check DECL_TEMPLATE_PARM_P in duplicate_decls [PR97511]

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This makes duplicate_decls differentiate a TYPE_DECL for an alias
template from a TYPE_DECL for one of its template parameters.  The
recently added assert in template_parm_to_arg revealed this latent issue
because merging of the two TYPE_DECLs cleared the DECL_TEMPLATE_PARM_P
flag.

With this patch, we now also correctly diagnose the name shadowing in
the below testcase (as required by [temp.local]/6).

gcc/cp/ChangeLog:

	PR c++/97511
	* decl.c (duplicate_decls): Return NULL_TREE if
	DECL_TEMPLATE_PARM_P differ.

gcc/testsuite/ChangeLog:

	PR c++/97511
	* g++.dg/template/shadow3.C: New test.
This commit is contained in:
Patrick Palka 2020-10-22 07:27:55 -04:00
parent 03e93e1efe
commit b083a14dfe
2 changed files with 7 additions and 0 deletions
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3
gcc/cp/decl.c
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@ -2002,6 +2002,9 @@ duplicate_decls (tree newdecl, tree olddecl, bool hiding, bool was_hidden)
|| DECL_IMPLICIT_TYPEDEF_P (newdecl)))
return NULL_TREE;
if (DECL_TEMPLATE_PARM_P (olddecl) != DECL_TEMPLATE_PARM_P (newdecl))
return NULL_TREE;
if (!validate_constexpr_redeclaration (olddecl, newdecl))
return error_mark_node;

4
gcc/testsuite/g++.dg/template/shadow3.C Normal file
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@ -0,0 +1,4 @@
// PR c++/97511
// { dg-do compile { target c++11 } }
template <class Z> using Z = Z; // { dg-error "shadow|declaration" }