On 1/23/25 10:15 AM, Nathaniel Shead wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?

-- >8 --

This fills in a hole left in r15-6378-g9016c5ac94c557 with regards to
detection of TU-local lambdas.  Now that LAMBDA_EXPR_EXTRA_SCOPE is
properly set for most lambdas we can use it to detect lambdas that are
TU-local.

Lambdas in concept definitions I believe should not be considered
TU-local, since they are always unevaluated and should never be emitted.
This patch gives these lambdas a mangling scope (though it will never be
actually used in name mangling).

This is now CWG2988 (https://cplusplus.github.io/CWG/issues/2988.html), please mention it in the commit message. OK with that change.

gcc/cp/ChangeLog:

        * cp-tree.h (finish_concept_definition): Adjust parameters.
        (start_concept_definition): Declare.
        * module.cc (depset::hash::is_tu_local_entity): Use
        LAMBDA_EXPR_EXTRA_SCOPE to detect TU-local lambdas.
        * parser.cc (cp_parser_concept_definition): Start a lambda scope
        for concept definitions.
        * pt.cc (tsubst_lambda_expr): Namespace-scope lambdas may now
        have extra scope.
        (finish_concept_definition): Split into...
        (start_concept_definition): ...this new function.

gcc/testsuite/ChangeLog:

        * g++.dg/modules/internal-4_b.C: Remove XFAILs, add new XFAIL
        for lambda alias.
        * g++.dg/modules/lambda-9.h: New test.
        * g++.dg/modules/lambda-9_a.H: New test.
        * g++.dg/modules/lambda-9_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
---
  gcc/cp/cp-tree.h                            |  3 ++-
  gcc/cp/module.cc                            | 15 +++++++++------
  gcc/cp/parser.cc                            | 14 +++++++++++++-
  gcc/cp/pt.cc                                | 21 +++++++++++++++------
  gcc/testsuite/g++.dg/modules/internal-4_b.C |  3 ++-
  gcc/testsuite/g++.dg/modules/lambda-9.h     |  2 ++
  gcc/testsuite/g++.dg/modules/lambda-9_a.H   |  4 ++++
  gcc/testsuite/g++.dg/modules/lambda-9_b.C   |  6 ++++++
  8 files changed, 53 insertions(+), 15 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/modules/lambda-9.h
  create mode 100644 gcc/testsuite/g++.dg/modules/lambda-9_a.H
  create mode 100644 gcc/testsuite/g++.dg/modules/lambda-9_b.C

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 1873b3d4ae0..16107f58759 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -8689,7 +8689,8 @@ struct diagnosing_failed_constraint
  extern cp_expr finish_constraint_or_expr      (location_t, cp_expr, cp_expr);
  extern cp_expr finish_constraint_and_expr     (location_t, cp_expr, cp_expr);
  extern cp_expr finish_constraint_primary_expr (cp_expr);
-extern tree finish_concept_definition          (cp_expr, tree, tree);
+extern tree start_concept_definition           (cp_expr);
+extern tree finish_concept_definition          (tree, tree, tree);
  extern tree combine_constraint_expressions      (tree, tree);
  extern tree append_constraint                 (tree, tree);
  extern tree get_constraints                     (const_tree);
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 17215594fd3..1c1eb2e37e2 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -11329,7 +11329,8 @@ trees_out::key_mergeable (int tag, merge_kind mk, tree 
decl, tree inner,
            gcc_checking_assert (TREE_CODE (scope) == VAR_DECL
                                 || TREE_CODE (scope) == FIELD_DECL
                                 || TREE_CODE (scope) == PARM_DECL
-                                || TREE_CODE (scope) == TYPE_DECL);
+                                || TREE_CODE (scope) == TYPE_DECL
+                                || TREE_CODE (scope) == CONCEPT_DECL);
            /* Lambdas attached to fields are keyed to the class.  */
            if (TREE_CODE (scope) == FIELD_DECL)
              scope = TYPE_NAME (DECL_CONTEXT (scope));
@@ -13435,9 +13436,10 @@ depset::hash::is_tu_local_entity (tree decl, bool 
explain/*=false*/)
        tree main_decl = TYPE_MAIN_DECL (type);
        if (!DECL_CLASS_SCOPE_P (main_decl)
          && !decl_function_context (main_decl)
-         /* FIXME: Lambdas defined outside initializers.  We'll need to more
-            thoroughly set LAMBDA_TYPE_EXTRA_SCOPE to check this.  */
-         && !LAMBDA_TYPE_P (type))
+         /* LAMBDA_EXPR_EXTRA_SCOPE will be set for lambdas defined in
+            contexts where they would not be TU-local.  */
+         && !(LAMBDA_TYPE_P (type)
+              && LAMBDA_TYPE_EXTRA_SCOPE (type)))
        {
          if (explain)
            inform (loc, "%qT has no name and is not defined within a class, "
@@ -20309,11 +20311,12 @@ maybe_key_decl (tree ctx, tree decl)
      return;
/* We only need to deal with lambdas attached to var, field,
-     parm, or type decls.  */
+     parm, type, or concept decls.  */
    if (TREE_CODE (ctx) != VAR_DECL
        && TREE_CODE (ctx) != FIELD_DECL
        && TREE_CODE (ctx) != PARM_DECL
-      && TREE_CODE (ctx) != TYPE_DECL)
+      && TREE_CODE (ctx) != TYPE_DECL
+      && TREE_CODE (ctx) != CONCEPT_DECL)
      return;
/* For fields, key it to the containing type to handle deduplication
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index ef7808476e1..e9bcb3ff8a0 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -31829,8 +31829,20 @@ cp_parser_concept_definition (cp_parser *parser)
        return error_mark_node;
      }
+ tree decl = start_concept_definition (id);
+  if (decl == error_mark_node)
+    {
+      cp_parser_skip_to_end_of_statement (parser);
+      cp_parser_consume_semicolon_at_end_of_statement (parser);
+      return error_mark_node;
+    }
+
    processing_constraint_expression_sentinel parsing_constraint;
+
+  start_lambda_scope (decl);
    tree init = cp_parser_constraint_expression (parser);
+  finish_lambda_scope ();
+
    if (init == error_mark_node)
      cp_parser_skip_to_end_of_statement (parser);
@@ -31838,7 +31850,7 @@ cp_parser_concept_definition (cp_parser *parser)
       but continue as if it were.  */
    cp_parser_consume_semicolon_at_end_of_statement (parser);
- return finish_concept_definition (id, init, attrs);
+  return finish_concept_definition (decl, init, attrs);
  }
// -------------------------------------------------------------------------- //
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 0f739d89b35..6442ae947c3 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -20231,7 +20231,7 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t 
complain, tree in_decl)
if (LAMBDA_EXPR_EXTRA_SCOPE (t))
      record_lambda_scope (r);
-  else if (TYPE_NAMESPACE_SCOPE_P (TREE_TYPE (t)))
+  if (TYPE_NAMESPACE_SCOPE_P (TREE_TYPE (t)))
      /* If we're pushed into another scope (PR105652), fix it.  */
      TYPE_CONTEXT (type) = DECL_CONTEXT (TYPE_NAME (type))
        = TYPE_CONTEXT (TREE_TYPE (t));
@@ -30027,12 +30027,10 @@ placeholder_type_constraint_dependent_p (tree t)
    return false;
  }
-/* Build and return a concept definition. Like other templates, the
-   CONCEPT_DECL node is wrapped by a TEMPLATE_DECL.  This returns the
-   the TEMPLATE_DECL. */
+/* Prepare and return a concept definition.  */
tree
-finish_concept_definition (cp_expr id, tree init, tree attrs)
+start_concept_definition (cp_expr id)
  {
    gcc_assert (identifier_p (id));
    gcc_assert (processing_template_decl);
@@ -30064,9 +30062,20 @@ finish_concept_definition (cp_expr id, tree init, tree 
attrs)
    /* Initially build the concept declaration; its type is bool.  */
    tree decl = build_lang_decl_loc (loc, CONCEPT_DECL, *id, boolean_type_node);
    DECL_CONTEXT (decl) = current_scope ();
-  DECL_INITIAL (decl) = init;
    TREE_PUBLIC (decl) = true;
+ return decl;
+}
+
+/* Finish building a concept definition. Like other templates, the
+   CONCEPT_DECL node is wrapped by a TEMPLATE_DECL.  This returns the
+   the TEMPLATE_DECL. */
+
+tree
+finish_concept_definition (tree decl, tree init, tree attrs)
+{
+  DECL_INITIAL (decl) = init;
+
    if (attrs)
      cplus_decl_attributes (&decl, attrs, 0);
diff --git a/gcc/testsuite/g++.dg/modules/internal-4_b.C b/gcc/testsuite/g++.dg/modules/internal-4_b.C
index 86bec294fc8..93cbbb16397 100644
--- a/gcc/testsuite/g++.dg/modules/internal-4_b.C
+++ b/gcc/testsuite/g++.dg/modules/internal-4_b.C
@@ -80,7 +80,8 @@ void in_function_body() { struct {} x; }  // OK
  auto in_initializer = []{};  // OK
#if __cplusplus >= 202002L
-decltype([]{}) d_lambda;  // { dg-error "exposes TU-local entity" "" { xfail 
*-*-* } }
+decltype([]{}) d_lambda;  // { dg-error "exposes TU-local entity" "" { target 
c++20 } }
+using alias_lambda = decltype([]{});  // { dg-error "exposes TU-local entity" 
"" { target c++20 } }
template <typename T>
  concept in_constraint_expression = requires {
diff --git a/gcc/testsuite/g++.dg/modules/lambda-9.h 
b/gcc/testsuite/g++.dg/modules/lambda-9.h
new file mode 100644
index 00000000000..4de9b7861c1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/lambda-9.h
@@ -0,0 +1,2 @@
+template <typename T>
+concept C = requires { []{}; };
diff --git a/gcc/testsuite/g++.dg/modules/lambda-9_a.H 
b/gcc/testsuite/g++.dg/modules/lambda-9_a.H
new file mode 100644
index 00000000000..da0fa3b31f2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/lambda-9_a.H
@@ -0,0 +1,4 @@
+// { dg-additional-options "-fmodule-header -std=c++20" }
+// { dg-module-cmi {} }
+
+#include "lambda-9.h"
diff --git a/gcc/testsuite/g++.dg/modules/lambda-9_b.C 
b/gcc/testsuite/g++.dg/modules/lambda-9_b.C
new file mode 100644
index 00000000000..6f2186421f7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/lambda-9_b.C
@@ -0,0 +1,6 @@
+// { dg-additional-options "-fmodules -std=c++20 -fno-module-lazy" }
+
+#include "lambda-9.h"
+import "lambda-9_a.H";
+
+static_assert(C<int>);

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