c++/modules: Treat unattached lambdas as TU-local [PR116568]

This fixes ICEs where unattached lambdas at class scope (for instance,
in member template instantiations) are streamed.  This is only possible
in header units, as in named modules attempting to stream such lambdas
will be an error.

	PR c++/116568

gcc/cp/ChangeLog:

	* module.cc (trees_out::get_merge_kind): Treat all lambdas
	without a mangling scope as un-mergeable.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/lambda-8.h: New test.
	* g++.dg/modules/lambda-8_a.H: New test.
	* g++.dg/modules/lambda-8_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>

Author: wreien

gcc/cp/module.cc

@@ -11014,18 +11014,23 @@ trees_out::get_merge_kind (tree decl, depset *dep)
 	       g++.dg/modules/lambda-6_a.C.  */
 	    if (DECL_IMPLICIT_TYPEDEF_P (STRIP_TEMPLATE (decl))
 		&& LAMBDA_TYPE_P (TREE_TYPE (decl)))
-	      if (tree scope = LAMBDA_TYPE_EXTRA_SCOPE (TREE_TYPE (decl)))
-		{
-		  /* Lambdas attached to fields are keyed to its class.  */
-		  if (TREE_CODE (scope) == FIELD_DECL)
-		    scope = TYPE_NAME (DECL_CONTEXT (scope));
-		  if (DECL_LANG_SPECIFIC (scope)
-		      && DECL_MODULE_KEYED_DECLS_P (scope))
-		    {
-		      mk = MK_keyed;
-		      break;
-		    }
-		}
+	      {
+		if (tree scope = LAMBDA_TYPE_EXTRA_SCOPE (TREE_TYPE (decl)))
+		  {
+		    /* Lambdas attached to fields are keyed to its class.  */
+		    if (TREE_CODE (scope) == FIELD_DECL)
+		      scope = TYPE_NAME (DECL_CONTEXT (scope));
+		    if (DECL_LANG_SPECIFIC (scope)
+			&& DECL_MODULE_KEYED_DECLS_P (scope))
+		      {
+			mk = MK_keyed;
+			break;
+		      }
+		  }
+		/* Lambdas not attached to any mangling scope are TU-local.  */
+		mk = MK_unique;
+		break;
+	      }
 
 	    if (TREE_CODE (decl) == TEMPLATE_DECL
 		&& DECL_UNINSTANTIATED_TEMPLATE_FRIEND_P (decl))

gcc/testsuite/g++.dg/modules/lambda-8.h

@@ -0,0 +1,8 @@
+// PR c++/116568
+
+template <typename> struct S {
+  template <typename> using t = decltype([]{});
+};
+
+// 't' does not currently have a mangling scope, but should not ICE
+using t = S<int>::t<int>;

gcc/testsuite/g++.dg/modules/lambda-8_a.H

@@ -0,0 +1,5 @@
+// PR c++/116568
+// { dg-additional-options "-fmodules-ts -std=c++20" }
+// { dg-module-cmi {} }
+
+#include "lambda-8.h"

gcc/testsuite/g++.dg/modules/lambda-8_b.C

@@ -0,0 +1,7 @@
+// PR c++/116568
+// { dg-additional-options "-fmodules-ts -fno-module-lazy -std=c++20" }
+
+#include "lambda-8.h"
+import "lambda-8_a.H";
+
+// { dg-error "conflicting global module declaration" "" { target *-*-* } 0 }