PING: Re: [PATCH] c++: provide #include hint for missing includes [PR110164]

[David Malcolm <dmalcolm@redhat.com>]

I'd like to ping this C++ FE patch for review:
    https://gcc.gnu.org/pipermail/gcc-patches/2023-June/621779.html

Thanks
Dave

On Wed, 2023-06-14 at 20:28 -0400, David Malcolm wrote:
> PR c++/110164 notes that in cases where we have a forward decl
> of a std library type such as:
> 
> std::array<int, 10> x;
> 
> we omit this diagnostic:
> 
> error: aggregate ‘std::array<int, 10> x’ has incomplete type and cannot be defined
> 
> This patch adds this hint to the diagnostic:
> 
> note: ‘std::array’ is defined in header ‘<array>’; this is probably fixable by adding ‘#include <array>’
> 
> Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
> OK for trunk?
> 
> gcc/cp/ChangeLog:
>         PR c++/110164
>         * cp-name-hint.h (maybe_suggest_missing_header): New decl.
>         * decl.cc: Define INCLUDE_MEMORY.  Add include of
>         "cp/cp-name-hint.h".
>         (start_decl_1): Call maybe_suggest_missing_header.
>         * name-lookup.cc (maybe_suggest_missing_header): Remove "static".
> 
> gcc/testsuite/ChangeLog:
>         PR c++/110164
>         * g++.dg/missing-header-pr110164.C: New test.
> ---
>  gcc/cp/cp-name-hint.h                          |  3 +++
>  gcc/cp/decl.cc                                 | 10 ++++++++++
>  gcc/cp/name-lookup.cc                          |  2 +-
>  gcc/testsuite/g++.dg/missing-header-pr110164.C | 10 ++++++++++
>  4 files changed, 24 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/g++.dg/missing-header-pr110164.C
> 
> diff --git a/gcc/cp/cp-name-hint.h b/gcc/cp/cp-name-hint.h
> index bfa7c53c8f6..e2387e23d1f 100644
> --- a/gcc/cp/cp-name-hint.h
> +++ b/gcc/cp/cp-name-hint.h
> @@ -32,6 +32,9 @@ along with GCC; see the file COPYING3.  If not see
>  
>  extern name_hint suggest_alternatives_for (location_t, tree, bool);
>  extern name_hint suggest_alternatives_in_other_namespaces (location_t, tree);
> +extern name_hint maybe_suggest_missing_header (location_t location,
> +                                              tree name,
> +                                              tree scope);
>  extern name_hint suggest_alternative_in_explicit_scope (location_t, tree, tree);
>  extern name_hint suggest_alternative_in_scoped_enum (tree, tree);
>  
> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> index a672e4844f1..504b08ec250 100644
> --- a/gcc/cp/decl.cc
> +++ b/gcc/cp/decl.cc
> @@ -27,6 +27,7 @@ along with GCC; see the file COPYING3.  If not see
>     line numbers.  For example, the CONST_DECLs for enum values.  */
>  
>  #include "config.h"
> +#define INCLUDE_MEMORY
>  #include "system.h"
>  #include "coretypes.h"
>  #include "target.h"
> @@ -46,6 +47,7 @@ along with GCC; see the file COPYING3.  If not see
>  #include "c-family/c-objc.h"
>  #include "c-family/c-pragma.h"
>  #include "c-family/c-ubsan.h"
> +#include "cp/cp-name-hint.h"
>  #include "debug.h"
>  #include "plugin.h"
>  #include "builtins.h"
> @@ -5995,7 +5997,11 @@ start_decl_1 (tree decl, bool initialized)
>         ;                       /* An auto type is ok.  */
>        else if (TREE_CODE (type) != ARRAY_TYPE)
>         {
> +         auto_diagnostic_group d;
>           error ("variable %q#D has initializer but incomplete type", decl);
> +         maybe_suggest_missing_header (input_location,
> +                                       TYPE_IDENTIFIER (type),
> +                                       TYPE_CONTEXT (type));
>           type = TREE_TYPE (decl) = error_mark_node;
>         }
>        else if (!COMPLETE_TYPE_P (complete_type (TREE_TYPE (type))))
> @@ -6011,8 +6017,12 @@ start_decl_1 (tree decl, bool initialized)
>         gcc_assert (CLASS_PLACEHOLDER_TEMPLATE (type));
>        else
>         {
> +         auto_diagnostic_group d;
>           error ("aggregate %q#D has incomplete type and cannot be defined",
>                  decl);
> +         maybe_suggest_missing_header (input_location,
> +                                       TYPE_IDENTIFIER (type),
> +                                       TYPE_CONTEXT (type));
>           /* Change the type so that assemble_variable will give
>              DECL an rtl we can live with: (mem (const_int 0)).  */
>           type = TREE_TYPE (decl) = error_mark_node;
> diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc
> index 6ac58a35b56..917b481c163 100644
> --- a/gcc/cp/name-lookup.cc
> +++ b/gcc/cp/name-lookup.cc
> @@ -6796,7 +6796,7 @@ maybe_suggest_missing_std_header (location_t location, tree name)
>     for NAME within SCOPE at LOCATION, or an empty name_hint if this isn't
>     applicable.  */
>  
> -static name_hint
> +name_hint
>  maybe_suggest_missing_header (location_t location, tree name, tree scope)
>  {
>    if (scope == NULL_TREE)
> diff --git a/gcc/testsuite/g++.dg/missing-header-pr110164.C b/gcc/testsuite/g++.dg/missing-header-pr110164.C
> new file mode 100644
> index 00000000000..15980071c38
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/missing-header-pr110164.C
> @@ -0,0 +1,10 @@
> +// { dg-require-effective-target c++11 }
> +
> +#include <map>
> +
> +std::array<int, 10> a1; /* { dg-error "incomplete type" } */
> +/* { dg-message "'std::array' is defined in header '<array>'; this is probably fixable by adding '#include <array>'" "hint" { target *-*-* } .-1 } */
> +
> +std::array<int, 10> a2 {5}; /* { dg-error "incomplete type" } */
> +/* { dg-message "'std::array' is defined in header '<array>'; this is probably fixable by adding '#include <array>'" "hint" { target *-*-* } .-1 } */
> +