From 9a16584beb312bfc493977e472dcb9d11ad5bc76 Mon Sep 17 00:00:00 2001
From: Nathaniel Shead <nathanieloshead@gmail.com>
Date: Wed, 14 May 2025 20:49:22 +1000
Subject: [PATCH] c++: Partially revert "Support lambdas attached to more
 places in modules" [PR118245]

r14-9232-g3685fae23bb008 broke the ABI for lambdas in base classes,
causing ICEs when different lambdas got given the same mangled name.

This patch reverts the parser.cc changes from that patch to restore the
old behaviour.  The properly fixed behaviour is available in GCC 15.1
with r15-7202-g8990070b4297b9, but that change was not suitable for
backporting.

	PR c++/118245

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_class_head): Remove lambda scope when
	parsing base classes.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/lambda-7_a.H: Expect the test to fail.
	* g++.dg/modules/lambda-7_b.C: Likewise.
	* g++.dg/modules/lambda-7_c.C: Likewise.
	* g++.dg/cpp2a/lambda-uneval23.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
---
 gcc/cp/parser.cc                             | 10 ++--------
 gcc/testsuite/g++.dg/cpp2a/lambda-uneval23.C |  7 +++++++
 gcc/testsuite/g++.dg/modules/lambda-7_a.H    |  2 +-
 gcc/testsuite/g++.dg/modules/lambda-7_b.C    |  1 +
 gcc/testsuite/g++.dg/modules/lambda-7_c.C    |  2 +-
 5 files changed, 12 insertions(+), 10 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-uneval23.C

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index ae97ae5c5f59..4a2c1f272a3a 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -27750,16 +27750,10 @@ cp_parser_class_head (cp_parser* parser,
   if (cp_lexer_next_token_is (parser->lexer, CPP_COLON))
     {
       if (type)
-	{
-	  pushclass (type);
-	  start_lambda_scope (TYPE_NAME (type));
-	}
+	pushclass (type);
       bases = cp_parser_base_clause (parser);
       if (type)
-	{
-	  finish_lambda_scope ();
-	  popclass ();
-	}
+	popclass ();
     }
   else
     bases = NULL_TREE;
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-uneval23.C b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval23.C
new file mode 100644
index 000000000000..fa009f53ff23
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval23.C
@@ -0,0 +1,7 @@
+// PR c++/118245
+// { dg-do compile { target c++20 } }
+
+template<auto> struct Cask {};
+struct T1 : Cask<[]{}> {
+  Cask<[]{}> c{};
+};
diff --git a/gcc/testsuite/g++.dg/modules/lambda-7_a.H b/gcc/testsuite/g++.dg/modules/lambda-7_a.H
index 5197114f76ca..842aedc5fd94 100644
--- a/gcc/testsuite/g++.dg/modules/lambda-7_a.H
+++ b/gcc/testsuite/g++.dg/modules/lambda-7_a.H
@@ -1,4 +1,4 @@
 // { dg-additional-options "-fmodule-header -Wno-subobject-linkage" }
-// { dg-module-cmi {} }
+// { dg-ice "see PR c++/118245" { c++20 } }
 
 #include "lambda-7.h"
diff --git a/gcc/testsuite/g++.dg/modules/lambda-7_b.C b/gcc/testsuite/g++.dg/modules/lambda-7_b.C
index 2d781e930678..cd4d0f3aa659 100644
--- a/gcc/testsuite/g++.dg/modules/lambda-7_b.C
+++ b/gcc/testsuite/g++.dg/modules/lambda-7_b.C
@@ -1,4 +1,5 @@
 // { dg-additional-options "-fmodules-ts -fno-module-lazy -Wno-subobject-linkage" }
+// { dg-xfail-if "see PR c++/118245" { c++20 } }
 // Test for ODR deduplication
 
 #include "lambda-7.h"
diff --git a/gcc/testsuite/g++.dg/modules/lambda-7_c.C b/gcc/testsuite/g++.dg/modules/lambda-7_c.C
index f283681fa96c..3fd159e08a76 100644
--- a/gcc/testsuite/g++.dg/modules/lambda-7_c.C
+++ b/gcc/testsuite/g++.dg/modules/lambda-7_c.C
@@ -1,5 +1,5 @@
-// { dg-module-do run }
 // { dg-additional-options "-fmodules-ts -fno-module-lazy -Wno-subobject-linkage" }
+// { dg-xfail-if "see PR c++/118245" { c++20 } }
 
 import "lambda-7_a.H";
 
-- 
2.47.2