Re: [PATCH] c++: Refer to internal linkage for -Wsubobject-linkage [PR86491]

[Jonathan Wakely <jwakely@redhat.com>]

ping
https://gcc.gnu.org/pipermail/gcc-patches/2022-June/597560.html

On Thu, 30 Jun 2022 at 17:53, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> Tested powerpc64le-linux, OK for trunk?
>
> -- >8 --
>
> Since C++11 relaxed the requirement for template arguments to have
> external linkage, it's possible to get -Wsubobject-linkage warnings
> without using any anonymous namespaces. This confuses users when they
> get diagnostics that refer to an anonymous namespace that doesn't exist
> in their code.
>
> This changes the diagnostic to say "has internal linkage" for C++11 and
> later, which is accurate whether internal linkage is due to the 'static'
> specifier, or due to the use of anonymous namespaces.
>
> For C++98 template arguments declared with 'static' are ill-formed
> anyway, so the only way this warning can arise is via anonymous
> namespaces. That means the existing wording is accurate for C++98 and so
> we can keep it.
>
>         PR c++/86491
>
> gcc/cp/ChangeLog:
>
>         * decl2.cc (constrain_class_visibility): Adjust wording of
>         -Wsubobject-linkage to account for cases where anonymous
>         namespaces aren't used.
>
> gcc/testsuite/ChangeLog:
>
>         * g++.dg/warn/Wsubobject-linkage-3.C: Adjust for new warning.
>         * g++.dg/warn/anonymous-namespace-1.C: Use separate dg-warning
>         directives for C++98 and everything else.
>         * g++.dg/warn/anonymous-namespace-2.C: Likewise.
>         * g++.dg/warn/anonymous-namespace-3.C: Likewise.
> ---
>  gcc/cp/decl2.cc                                   | 12 ++++++++++--
>  gcc/testsuite/g++.dg/warn/Wsubobject-linkage-3.C  |  4 ++--
>  gcc/testsuite/g++.dg/warn/anonymous-namespace-1.C |  8 ++++++--
>  gcc/testsuite/g++.dg/warn/anonymous-namespace-2.C |  9 ++++++---
>  gcc/testsuite/g++.dg/warn/anonymous-namespace-3.C |  3 ++-
>  5 files changed, 26 insertions(+), 10 deletions(-)
>
> diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
> index 3737e5f010c..de53678715e 100644
> --- a/gcc/cp/decl2.cc
> +++ b/gcc/cp/decl2.cc
> @@ -3027,7 +3027,11 @@ constrain_class_visibility (tree type)
>  %qT has a field %qD whose type depends on the type %qT which has no linkage",
>                                type, t, nlt);
>                   }
> -               else
> +               else if (cxx_dialect > cxx98)
> +                 warning (OPT_Wsubobject_linkage, "\
> +%qT has a field %qD whose type has internal linkage",
> +                          type, t);
> +               else // In C++98 this can only happen with unnamed namespaces.
>                   warning (OPT_Wsubobject_linkage, "\
>  %qT has a field %qD whose type uses the anonymous namespace",
>                            type, t);
> @@ -3062,7 +3066,11 @@ constrain_class_visibility (tree type)
>  %qT has a base %qT whose type depends on the type %qT which has no linkage",
>                              type, TREE_TYPE (t), nlt);
>                 }
> -             else
> +             else if (cxx_dialect > cxx98)
> +               warning (OPT_Wsubobject_linkage, "\
> +%qT has a base %qT whose type has internal linkage",
> +                        type, TREE_TYPE (t));
> +             else // In C++98 this can only happen with unnamed namespaces.
>                 warning (OPT_Wsubobject_linkage, "\
>  %qT has a base %qT whose type uses the anonymous namespace",
>                          type, TREE_TYPE (t));
> diff --git a/gcc/testsuite/g++.dg/warn/Wsubobject-linkage-3.C b/gcc/testsuite/g++.dg/warn/Wsubobject-linkage-3.C
> index 95a04501441..b116fbbb186 100644
> --- a/gcc/testsuite/g++.dg/warn/Wsubobject-linkage-3.C
> +++ b/gcc/testsuite/g++.dg/warn/Wsubobject-linkage-3.C
> @@ -3,7 +3,7 @@
>  namespace { struct Foo { }; }
>
>  #line 6 "foo.C"
> -struct Bar { Foo foo; };   // { dg-warning "anonymous namespace" }
> +struct Bar { Foo foo; };   // { dg-warning "anonymous namespace|internal linkage" }
>  // { dg-bogus "no linkage" "" { target *-*-* } .-1 }
> -struct Bar2 : Foo { };     // { dg-warning "anonymous namespace" }
> +struct Bar2 : Foo { };     // { dg-warning "anonymous namespace|internal linkage" }
>  // { dg-bogus "no linkage" "" { target *-*-* } .-1 }
> diff --git a/gcc/testsuite/g++.dg/warn/anonymous-namespace-1.C b/gcc/testsuite/g++.dg/warn/anonymous-namespace-1.C
> index cf193e0cba5..eed3818c5cf 100644
> --- a/gcc/testsuite/g++.dg/warn/anonymous-namespace-1.C
> +++ b/gcc/testsuite/g++.dg/warn/anonymous-namespace-1.C
> @@ -14,5 +14,9 @@ class foobar1
>  };
>
>  #line 17 "foo.C"
> -class foobar : public bad { }; // { dg-warning "uses the anonymous namespace" }
> -class foobar2 { bad b; }; // { dg-warning "uses the anonymous namespace" }
> +class foobar : public bad { };
> +// { dg-warning "has internal linkage" "" { target c++11 } .-1 }
> +// { dg-warning "uses the anonymous namespace" "" { target c++98_only } .-2 }
> +class foobar2 { bad b; };
> +// { dg-warning "has internal linkage" "" { target c++11 } .-1 }
> +// { dg-warning "uses the anonymous namespace" "" { target c++98_only } .-2 }
> diff --git a/gcc/testsuite/g++.dg/warn/anonymous-namespace-2.C b/gcc/testsuite/g++.dg/warn/anonymous-namespace-2.C
> index 4048f3959df..f2ca5915278 100644
> --- a/gcc/testsuite/g++.dg/warn/anonymous-namespace-2.C
> +++ b/gcc/testsuite/g++.dg/warn/anonymous-namespace-2.C
> @@ -18,12 +18,15 @@ struct g3 {
>  };
>
>  #line 21 "foo.C"
> -struct b1 { // { dg-warning "uses the anonymous namespace" }
> +struct b1 { // { dg-warning "has internal linkage" "" { target c++11 } }
> +// { dg-warning "uses the anonymous namespace" "" { target c++98_only } .-1 }
>      bad * B;
>  };
> -struct b2 { // { dg-warning "uses the anonymous namespace" }
> +struct b2 { // { dg-warning "has internal linkage" "" { target c++11 } }
> +// { dg-warning "uses the anonymous namespace" "" { target c++98_only } .-1 }
>      bad * B[1];
>  };
> -struct b3 { // { dg-warning "uses the anonymous namespace" }
> +struct b3 { // { dg-warning "has internal linkage" "" { target c++11 } }
> +// { dg-warning "uses the anonymous namespace" "" { target c++98_only } .-1 }
>      bad (*B)[1];
>  };
> diff --git a/gcc/testsuite/g++.dg/warn/anonymous-namespace-3.C b/gcc/testsuite/g++.dg/warn/anonymous-namespace-3.C
> index 8b72abdf5d1..ce5745b25f0 100644
> --- a/gcc/testsuite/g++.dg/warn/anonymous-namespace-3.C
> +++ b/gcc/testsuite/g++.dg/warn/anonymous-namespace-3.C
> @@ -7,7 +7,8 @@
>  struct B { std::auto_ptr<A> p; };
>
>  #line 10 "foo.C"
> -struct C                  // { dg-warning "uses the anonymous namespace" }
> +struct C // { dg-warning "has internal linkage" "" { target c++11 } }
> +// { dg-warning "uses the anonymous namespace" "" { target c++98_only } .-1 }
>  {
>    std::auto_ptr<A> p;
>  };
> --
> 2.36.1
>