c++: nested generic lambda in DMI [PR101717]

We were already checking COMPLETE_TYPE_P to recognize instantiation of a
generic lambda, but didn't consider that we might be nested in a non-generic
lambda.

	PR c++/101717

gcc/cp/ChangeLog:

	* lambda.cc (lambda_expr_this_capture): Check all enclosing
	lambdas for completeness.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/lambda-generic-this4.C: New test.

1 files changed, 7 insertions, 1 deletions

diff --git a/gcc/cp/lambda.cc b/gcc/cp/lambda.cc
index 4cc3a47..f22798d 100644
--- a/gcc/cp/lambda.cc
+++ b/gcc/cp/lambda.cc
@@ -741,6 +741,7 @@ lambda_expr_this_capture (tree lambda, int add_capture_p)
     {
       tree lambda_stack = NULL_TREE;
       tree init = NULL_TREE;
+      bool saw_complete = false;
 
       /* If we are in a lambda function, we can move out until we hit:
            1. a non-lambda function or NSDMI,
@@ -759,6 +760,11 @@ lambda_expr_this_capture (tree lambda, int add_capture_p)
 				      lambda_stack);
 
 	  tree closure = LAMBDA_EXPR_CLOSURE (tlambda);
+	  if (COMPLETE_TYPE_P (closure))
+	    /* We're instantiating a generic lambda op(), the containing
+	       scope may be gone.  */
+	    saw_complete = true;
+
 	  tree containing_function
 	    = decl_function_context (TYPE_NAME (closure));
 
@@ -768,7 +774,7 @@ lambda_expr_this_capture (tree lambda, int add_capture_p)
 	      /* Lambda in an NSDMI.  We don't have a function to look up
 		 'this' in, but we can find (or rebuild) the fake one from
 		 inject_this_parameter.  */
-	      if (!containing_function && !COMPLETE_TYPE_P (closure))
+	      if (!containing_function && !saw_complete)
 		/* If we're parsing a lambda in a non-local class,
 		   we can find the fake 'this' in scope_chain.  */
 		init = scope_chain->x_current_class_ptr;