On 6/22/23 11:50, Marek Polacek wrote:
On Wed, Jun 21, 2023 at 04:44:00PM -0400, David Malcolm via Gcc-patches wrote:
I'd like to ping this C++ FE patch for review:
     https://gcc.gnu.org/pipermail/gcc-patches/2023-June/621779.html

Not an approval, but LGTM, though some nits below:
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);

The enclosing decls omit the parameter names; if you do that, it may
fit on one line.

  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));

Maybe CP_TYPE_CONTEXT?

           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));

Here as well.

           /* 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

Can we put the new test into g++.dg/diagnostic/?

OK with the tweaks Marek suggests.

Jason

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