* [C++ PATCH] Fix unnecessary error when top-level cv-qualifiers is dropped (PR c++/101783)
@ 2021-08-10 2:33 nick huang
0 siblings, 0 replies; only message in thread
From: nick huang @ 2021-08-10 2:33 UTC (permalink / raw)
To: 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 <nickhuang99@hotmail.com>
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 00000000000..8f8f8b1faeb
--- /dev/null
+++ gcc/testsuite/g++.dg/parse/pr101783.C
@@ -0,0 +1,10 @@
+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){}
+struct B{};
+template<>
+void f<B>(const A<B>::Type){}
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