c++: cv-qualified ref introduced by typedef [PR101783]

The root cause of this bug is that it considers reference with
cv-qualifiers as an error by generating value for variable "bad_quals".
However, this is not correct for case of typedef. Here I quote spec
[dcl.ref]/1 :
"Cv-qualified references are ill-formed except when the cv-qualifiers
are introduced through the use of a typedef-name ([dcl.typedef],
[temp.param]) or decltype-specifier ([dcl.type.decltype]),
in which case the cv-qualifiers are ignored."

2021-09-30  qingzhe huang  <nickhuang99@hotmail.com>

gcc/cp/ChangeLog:
	PR c++/101783
	* tree.c (cp_build_qualified_type_real): Exclude typedef from
	error.

gcc/testsuite/ChangeLog:
	PR c++/101783
	* g++.dg/parse/pr101783.C: New test.

diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index 3c62dd74380146ee7ec045f1bca04bfd5e310c34..d67d7856e7c28ed684aba637f22a16830e53aaff 100644 (file)
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -1403,11 +1403,18 @@ cp_build_qualified_type_real (tree type,
   /* A reference or method type shall not be cv-qualified.
      [dcl.ref], [dcl.fct].  This used to be an error, but as of DR 295
      (in CD1) we always ignore extra cv-quals on functions.  */
+
+  /* [dcl.ref/1] Cv-qualified references are ill-formed except when
+     the cv-qualifiers are introduced through the use of a typedef-name
+     ([dcl.typedef], [temp.param]) or decltype-specifier
+     ([dcl.type.decltype]),in which case the cv-qualifiers are
+     ignored.  */
   if (type_quals & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE)
       && (TYPE_REF_P (type)
          || FUNC_OR_METHOD_TYPE_P (type)))
     {
-      if (TYPE_REF_P (type))
+      if (TYPE_REF_P (type)
+         && (!typedef_variant_p (type) || FUNC_OR_METHOD_TYPE_P (type)))
        bad_quals |= type_quals & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE);
       type_quals &= ~(TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE);
     }

diff --git a/gcc/testsuite/g++.dg/parse/pr101783.C b/gcc/testsuite/g++.dg/parse/pr101783.C
new file mode 100644 (file)
index 0000000..4e0a435
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/pr101783.C
@@ -0,0 +1,5 @@
+template<class T> struct A{
+        typedef T& Type;
+};
+template<class T> void f(const typename A<T>::Type){}
+template <> void f<int>(const typename A<int>::Type){}