[gcc r10-10721] c++: nested generic lambda in DMI [PR101717]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:20dc7a2119cc0a4e5ddc4a6899a7350621f05440

commit r10-10721-g20dc7a2119cc0a4e5ddc4a6899a7350621f05440
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Apr 6 22:20:49 2022 -0400

    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.c (lambda_expr_this_capture): Check all enclosing
            lambdas for completeness.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp1y/lambda-generic-this4.C: New test.

Diff:
---
 gcc/cp/lambda.c                                   | 8 +++++++-
 gcc/testsuite/g++.dg/cpp1y/lambda-generic-this4.C | 7 +++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/lambda.c b/gcc/cp/lambda.c
index f143cec61d3..1b0cd869fe3 100644
--- a/gcc/cp/lambda.c
+++ b/gcc/cp/lambda.c
@@ -743,6 +743,7 @@ 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,
@@ -761,6 +762,11 @@ 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));
 
@@ -770,7 +776,7 @@ 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;
diff --git a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-this4.C b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-this4.C
new file mode 100644
index 00000000000..38d582bec5e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-this4.C
@@ -0,0 +1,7 @@
+// PR c++/101717
+// { dg-do compile { target c++14 } }
+
+struct x {
+  static void f() { }
+  void (*_)() = [] { [=](auto) { f(); }(0); };
+};