Re: [PATCH] c++: Fix up modules handling of namespace scope structured bindings

[Jason Merrill]

On 1/7/25 2:48 PM, Jakub Jelinek wrote:

Hi!

With the following patch I actually get a simple namespace scope structured
binding working with modules.

The core_vals change ensure we actually save/restore DECL_VALUE_EXPR even
for namespace scope vars, the get_merge_kind is based on the assumption
that structured bindings are always unique, one can't redeclare them and
without it we really ICE because their base vars have no name.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

2025-01-07  Jakub Jelinek  <ja...@redhat.com>

        * module.cc (trees_out::core_vals): Note DECL_VALUE_EXPR even for
        vars outside of functions.
        (trees_in::core_vals): Read in DECL_VALUE_EXPR even for vars outside
        of functions.
        (trees_out::get_merge_kind): Make DECL_DECOMPOSITION_P MK_unique.

        * g++.dg/modules/decomp-2_b.C: New test.
        * g++.dg/modules/decomp-2_a.H: New file.

--- gcc/cp/module.cc.jj 2025-01-03 17:54:12.411905971 +0100
+++ gcc/cp/module.cc    2025-01-07 13:42:45.495623879 +0100
@@ -6313,7 +6313,11 @@ trees_out::core_vals (tree t)
      case VAR_DECL:
        if (DECL_CONTEXT (t)
          && TREE_CODE (DECL_CONTEXT (t)) != FUNCTION_DECL)
-       break;
+       {
+         if (DECL_HAS_VALUE_EXPR_P (t))
+           WT (DECL_VALUE_EXPR (t));
+         break;
+       }
        /* FALLTHROUGH  */

case RESULT_DECL:

@@ -6843,7 +6847,14 @@ trees_in::core_vals (tree t)
      case VAR_DECL:
        if (DECL_CONTEXT (t)
          && TREE_CODE (DECL_CONTEXT (t)) != FUNCTION_DECL)
-       break;
+       {
+         if (DECL_HAS_VALUE_EXPR_P (t))
+           {
+             tree val = tree_node ();
+             SET_DECL_VALUE_EXPR (t, val);
+           }
+         break;
+       }
        /* FALLTHROUGH  */

case RESULT_DECL:

@@ -10985,6 +10996,12 @@ trees_out::get_merge_kind (tree decl, de
                break;
              }

+ if (DECL_DECOMPOSITION_P (decl))

+             {
+               mk = MK_unique;
+               break;
+             }
+
            if (IDENTIFIER_ANON_P (DECL_NAME (decl)))
              {
                if (RECORD_OR_UNION_TYPE_P (ctx))
--- gcc/testsuite/g++.dg/modules/decomp-2_b.C.jj        2025-01-07 
13:27:32.352323501 +0100
+++ gcc/testsuite/g++.dg/modules/decomp-2_b.C   2025-01-07 13:27:32.352323501 
+0100
@@ -0,0 +1,11 @@
+// { dg-do run }
+// { dg-additional-options "-fmodules-ts" }
+
+import "decomp-2_a.H";
+
+int
+main ()
+{
+  if (a != 1 || b != 2 || c != 3)
+    __builtin_abort ();
+}
--- gcc/testsuite/g++.dg/modules/decomp-2_a.H.jj        2025-01-07 
13:27:32.352323501 +0100
+++ gcc/testsuite/g++.dg/modules/decomp-2_a.H   2025-01-07 13:27:32.352323501 
+0100
@@ -0,0 +1,11 @@
+// { dg-additional-options -fmodule-header }
+// { dg-module-cmi {} }
+
+struct A {
+  int a, b, c;
+};
+
+namespace {
+A d = { 1, 2, 3 };
+auto [a, b, c] = d;
+}

        Jakub