On Thu, Nov 03, 2022 at 03:22:12PM -0400, Jason Merrill wrote:
> On 11/1/22 13:01, Marek Polacek wrote:
> > It seems wrong to issue a -Wignored-qualifiers warning for code like:
> >
> > static_assert(!is_same_v<void(*)(), const void(*)()>);
> >
> > because there the qualifier matters. Likewise in template
> > specialization:
> >
> > template<typename T> struct S { };
> > template<> struct S<void(*)()> { };
> > template<> struct S<const void(*)()> { }; // OK, not a redefinition
> >
> > I'm of the mind that we should disable the warning for template
> > arguments, as in the patch below.
>
> Hmm, I'm not sure why we would want to treat template arguments differently
> from other type-ids. Maybe only warn if funcdecl_p?
I think that makes sense. There are other contexts in which cv-quals
matter, for instance trailing-return-type. Updated patch below, plus
I've extended the testcase. Thanks,
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
It seems wrong to issue a -Wignored-qualifiers warning for code like:
static_assert(!is_same_v<void(*)(), const void(*)()>);
because there the qualifier matters. Likewise in template
specialization:
template<typename T> struct S { };
template<> struct S<void(*)()> { };
template<> struct S<const void(*)()> { }; // OK, not a redefinition
And likewise in other type-id contexts such as trailing-return-type:
auto g() -> const void (*)();
This patch limits the warning to the function declaration context only.
PR c++/107492
gcc/cp/ChangeLog:
* decl.cc (grokdeclarator): Only emit a -Wignored-qualifiers warning
when funcdecl_p.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wignored-qualifiers3.C: New test.
---
gcc/cp/decl.cc | 6 ++++-
.../g++.dg/warn/Wignored-qualifiers3.C | 24 +++++++++++++++++++
2 files changed, 29 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Wignored-qualifiers3.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 890cfcabd35..67b9f24d7d6 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -13038,7 +13038,11 @@ grokdeclarator (const cp_declarator *declarator,
if (type_quals != TYPE_UNQUALIFIED)
{
- if (SCALAR_TYPE_P (type) || VOID_TYPE_P (type))
+ /* It's wrong, for instance, to issue a -Wignored-qualifiers
+ warning for
+ static_assert(!is_same_v<void(*)(), const void(*)()>);
+ because there the qualifier matters. */
+ if (funcdecl_p && (SCALAR_TYPE_P (type) || VOID_TYPE_P (type)))
warning_at (typespec_loc, OPT_Wignored_qualifiers, "type "
"qualifiers ignored on function return type");
/* [dcl.fct] "A volatile-qualified return type is
diff --git a/gcc/testsuite/g++.dg/warn/Wignored-qualifiers3.C
b/gcc/testsuite/g++.dg/warn/Wignored-qualifiers3.C
new file mode 100644
index 00000000000..dedb38fc995
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wignored-qualifiers3.C
@@ -0,0 +1,24 @@
+// PR c++/107492
+// { dg-do compile { target c++14 } }
+// { dg-additional-options "-Wignored-qualifiers" }
+
+// Here the 'const' matters, so don't warn.
+template<typename T> struct S { };
+template<> struct S<void(*)()> { };
+template<> struct S<const void(*)()> { }; // { dg-bogus "ignored" }
+
+template<typename T, typename U> constexpr bool is_same_v = false;
+template<typename T> constexpr bool is_same_v<T, T> = true;
+
+static_assert( ! is_same_v< void(*)(), const void(*)() >, ""); // { dg-bogus
"ignored" }
+
+// Here the 'const' matters as well -> don't warn.
+auto g() -> const void (*)(); // { dg-bogus "ignored" }
+auto g() -> const void (*)() { return nullptr; } // { dg-bogus "ignored" }
+
+// Here as well.
+const void (*h)() = static_cast<const void (*)()>(h); // { dg-bogus "ignored" }
+
+// But let's keep the warning here.
+const void f(); // { dg-warning "ignored" }
+const void f() { } // { dg-warning "ignored" }
base-commit: c41bbfcaf9d6ef5b57a7e89bba70b861c08a686b
--
2.38.1
