Re: [PATCH] c++: Fix unnecessary error when top-level cv-qualifiers is dropped [PR101783]

[Jonathan Wakely via Gcc-patches]

>PR c++/101387
>
>gcc/cp/ChangeLog:
>PR c++/101387
>* tree.c (cp_build_qualified_type_real): Excluding typedef from error
>
>gcc/testsuite/ChangeLog:
>PR c++/101387
>* g++.dg/parse/pr101783.C: New test.

This is the wrong PR number.

How has this ptch been tested? Have you bootstrapped the compiler and
run the full testsuite?

[PATCH] c++: Fix unnecessary error when top-level cv-qualifiers is dropped [PR101783]

[nick huang via Gcc-patches]

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:
"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."

2021-08-09  Qingzhe Huang  

PR c++/101387

gcc/cp/ChangeLog:
PR c++/101387
* tree.c (cp_build_qualified_type_real): Excluding typedef from error

gcc/testsuite/ChangeLog:
PR c++/101387
* g++.dg/parse/pr101783.C: New test.

diff --git gcc/cp/tree.c gcc/cp/tree.c
index 10b818d1370..a4ae3eee6d0 100644
--- gcc/cp/tree.c
+++ gcc/cp/tree.c
@@ -1361,11 +1361,18 @@ 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.  */
+  /* 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)
+   //A reference from typedef is not an error, but ignored.
+   && (!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 gcc/testsuite/g++.dg/parse/pr101783.C 
gcc/testsuite/g++.dg/parse/pr101783.C
new file mode 100644
index 000..8f8f8b1faeb
--- /dev/null
+++ gcc/testsuite/g++.dg/parse/pr101783.C
@@ -0,0 +1,10 @@
+template struct A{
+typedef T& Type;
+};
+template
+void f(const typename A::Type){}
+template<>
+void f(const typename A::Type){}
+struct B{};
+template<>
+void f(const A::Type){}