On 11/14/22 14:33, Marek Polacek wrote:
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.
Well, technically they matter in all contexts, including function
declaration:
const void f();
template <class T, class U> struct same;
template <class T> struct same<T,T>{};
same<decltype(f),const void()> s;
but much more likely to be a confused user in that case, whereas in a
template context it's likely to be some deep magic. :)
Updated patch below, plus I've extended the testcase. Thanks,
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
OK.
-- >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
