Eric Gallager via Gcc-patches <gcc-patches@gcc.gnu.org> writes:

> On Wed, Jun 14, 2023 at 8:29 PM David Malcolm via Gcc-patches
> <gcc-patches@gcc.gnu.org> 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>’
>>
>
> ..."probably"?
>

Right now, our fixit says:
```
/tmp/foo.c:1:1: note: ‘time_t’ is defined in header ‘<ctime>’; did you forget to ‘#include <ctime>’?
```

We should probably use the same phrasing for consistency?

>> 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 } */
>> +
>> --
>> 2.26.3
>>