[PATCH] c++: Fix bogus warning in deprecated namespace [PR99318]

[Jason Merrill]

On 3/9/21 10:22 PM, Marek Polacek wrote:
> In GCC 10, I introduced cp_warn_deprecated_use_scopes so that we can
> handle attribute deprecated on a namespace declaration.  This
> function walks the decl's contexts so that we warn for code like
> 
>    namespace [[deprecated]] N { struct S { }; }
>    N::S s;
> 
> We call cp_warn_deprecated_use_scopes when we encounter a TYPE_DECL.

Hmm, I'd think we should warn about N as a consequence of seeing N::, 
not because we are using S.  For instance, in

namespace [[deprecated]] N { struct S { }; }
using namespace N;
S s;

we should warn about the using-directive, but not also the declaration 
of 's'.

But the patch is OK, that's just a possible future direction.

> But in the following testcase we have a TYPE_DECL whose context is
> a deprecated function; that itself is not a reason to warn.  This
> patch limits for which entities we call cp_warn_deprecated_use;
> essentially it's what can follow ::.
> 
> I noticed that we didn't test that
> 
>    struct [[deprecated]] S { static void fn(); };
>    S::fn();
> 
> produces the expected warning, so I've added gen-attrs-73.C.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/10?
> 
> gcc/cp/ChangeLog:
> 
> 	PR c++/99318
> 	* decl2.c (cp_warn_deprecated_use_scopes): Only call
> 	cp_warn_deprecated_use when decl is a namespace, class, or enum.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/99318
> 	* g++.dg/cpp0x/attributes-namespace6.C: New test.
> 	* g++.dg/cpp0x/gen-attrs-73.C: New test.
> ---
>   gcc/cp/decl2.c                                |  3 ++-
>   .../g++.dg/cpp0x/attributes-namespace6.C      | 21 +++++++++++++++++++
>   gcc/testsuite/g++.dg/cpp0x/gen-attrs-73.C     | 20 ++++++++++++++++++
>   3 files changed, 43 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/attributes-namespace6.C
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/gen-attrs-73.C
> 
> diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
> index c46100de89a..ef79f6cc6d1 100644
> --- a/gcc/cp/decl2.c
> +++ b/gcc/cp/decl2.c
> @@ -5529,7 +5529,8 @@ cp_warn_deprecated_use_scopes (tree scope)
>   	 && scope != error_mark_node
>   	 && scope != global_namespace)
>       {
> -      if (cp_warn_deprecated_use (scope))
> +      if ((TREE_CODE (scope) == NAMESPACE_DECL || OVERLOAD_TYPE_P (scope))
> +	  && cp_warn_deprecated_use (scope))
>   	return;
>         if (TYPE_P (scope))
>   	scope = CP_TYPE_CONTEXT (scope);
> diff --git a/gcc/testsuite/g++.dg/cpp0x/attributes-namespace6.C b/gcc/testsuite/g++.dg/cpp0x/attributes-namespace6.C
> new file mode 100644
> index 00000000000..2fbc8e1158f
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/attributes-namespace6.C
> @@ -0,0 +1,21 @@
> +// PR c++/99318
> +// { dg-do compile { target c++11 } }
> +
> +template <typename T>
> +struct S {
> +    [[deprecated("foo")]] unsigned m_fn (char const chr)
> +    {
> +        using index_t = unsigned;
> +        return T::arr[static_cast<index_t>(chr)]; // { dg-bogus "deprecated" }
> +    }
> +};
> +
> +extern unsigned int arr[];
> +
> +struct R {
> +    [[deprecated("foo")]] unsigned m_fn (char const chr)
> +    {
> +        using index_t = unsigned;
> +        return arr[static_cast<index_t>(chr)]; // { dg-bogus "deprecated" }
> +    }
> +};
> diff --git a/gcc/testsuite/g++.dg/cpp0x/gen-attrs-73.C b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-73.C
> new file mode 100644
> index 00000000000..75f4077af7b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-73.C
> @@ -0,0 +1,20 @@
> +// { dg-do compile { target c++11 } }
> +// Test attribute deprecated on :: with class, enum, and namespace.
> +
> +struct [[deprecated]] S { static void fn(); static const int s = 0; };
> +union [[deprecated]] U { static void fn(); static const int u = 0; };
> +enum [[deprecated]] E { X };
> +enum class [[deprecated]] SE { Y };
> +namespace [[deprecated]] N { struct S { }; }
> +
> +void
> +g ()
> +{
> +  S::fn(); // { dg-warning "deprecated" }
> +  (void) S::s; // { dg-warning "deprecated" }
> +  U::fn(); // { dg-warning "deprecated" }
> +  (void) U::u; // { dg-warning "deprecated" }
> +  (void) E::X; // { dg-warning "deprecated" }
> +  (void) SE::Y; // { dg-warning "deprecated" }
> +  N::S s; // { dg-warning "deprecated" }
> +}
> 
> base-commit: 63d74fed4566f1de583c368ecb9e2fc423fb1c87
>