[gcc r12-8021] c++: -Wshadow=compatible-local type vs var [PR100608]

[Jason Merrill]

https://gcc.gnu.org/g:fd0024e48e94008915a6b18112efbbd8abc81ed8

commit r12-8021-gfd0024e48e94008915a6b18112efbbd8abc81ed8
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Apr 5 16:02:04 2022 -0400

    c++: -Wshadow=compatible-local type vs var [PR100608]
    
    The patch for PR92024 changed -Wshadow=compatible-local to warn if either
    new or old decl was a type, but the rationale only talked about the case
    where both are types.  If only one is, they aren't compatible.
    
            PR c++/100608
    
    gcc/cp/ChangeLog:
    
            * name-lookup.cc (check_local_shadow): Use -Wshadow=local
            if exactly one of 'old' and 'decl' is a type.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/warn/Wshadow-compatible-local-3.C: New test.

Diff:
---
 gcc/cp/name-lookup.cc                                  |  4 ++++
 gcc/testsuite/g++.dg/warn/Wshadow-compatible-local-3.C | 10 ++++++++++
 2 files changed, 14 insertions(+)

diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc
index c833b84ca8a..d16c577c029 100644
--- a/gcc/cp/name-lookup.cc
+++ b/gcc/cp/name-lookup.cc
@@ -3249,6 +3249,10 @@ check_local_shadow (tree decl)
       enum opt_code warning_code;
       if (warn_shadow)
 	warning_code = OPT_Wshadow;
+      else if ((TREE_CODE (decl) == TYPE_DECL)
+	       ^ (TREE_CODE (old) == TYPE_DECL))
+	/* If exactly one is a type, they aren't compatible.  */
+	warning_code = OPT_Wshadow_local;
       else if ((TREE_TYPE (old)
 		&& TREE_TYPE (decl)
 		&& same_type_p (TREE_TYPE (old), TREE_TYPE (decl)))
diff --git a/gcc/testsuite/g++.dg/warn/Wshadow-compatible-local-3.C b/gcc/testsuite/g++.dg/warn/Wshadow-compatible-local-3.C
new file mode 100644
index 00000000000..0e5ece74b37
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wshadow-compatible-local-3.C
@@ -0,0 +1,10 @@
+// PR c++/100608
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-Wshadow=compatible-local" }
+
+template <typename> class X {};
+
+void foo()
+{
+  auto a = X<class a>{};	// no warning, not compatible
+}