PR c++/82053 - ICE with default argument in lambda in template

	* pt.c (tsubst_arg_types): Substitute default arguments for lambdas
	in templates.
	(retrieve_specialization): Use lambda_fn_in_template_p.
	* cp-tree.h: Declare it.

From-SVN: r251826

gcc/cp/ChangeLog

 2017-09-06  Jason Merrill  <jason@redhat.com>
 
+	PR c++/82053 - ICE with default argument in lambda in template
+	* pt.c (tsubst_arg_types): Substitute default arguments for lambdas
+	in templates.
+	(retrieve_specialization): Use lambda_fn_in_template_p.
+	* cp-tree.h: Declare it.
+
 	PR c++/82070 - error with nested lambda capture
 	* pt.c (tsubst_expr) [DECL_EXPR]: Register capture proxies with
 	register_local_specialization.

gcc/cp/cp-tree.h

@@ -6821,6 +6821,7 @@ extern tree current_nonlambda_function		(void);
 extern tree nonlambda_method_basetype		(void);
 extern tree current_nonlambda_scope		(void);
 extern bool generic_lambda_fn_p			(tree);
+extern bool lambda_fn_in_template_p		(tree);
 extern void maybe_add_lambda_conv_op            (tree);
 extern bool is_lambda_ignored_entity            (tree);
 extern bool lambda_static_thunk_p		(tree);

gcc/cp/pt.c

@@ -1193,16 +1193,8 @@ retrieve_specialization (tree tmpl, tree args, hashval_t hash)
 
   /* Lambda functions in templates aren't instantiated normally, but through
      tsubst_lambda_expr.  */
-  if (LAMBDA_FUNCTION_P (tmpl))
-    {
-      bool generic = PRIMARY_TEMPLATE_P (tmpl);
-      if (TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (tmpl)) > generic)
-	return NULL_TREE;
-
-      /* But generic lambda functions are instantiated normally, once their
-	 containing context is fully instantiated.  */
-      gcc_assert (generic);
-    }
+  if (lambda_fn_in_template_p (tmpl))
+    return NULL_TREE;
 
   if (optimize_specialization_lookup_p (tmpl))
     {
@@ -12579,7 +12571,7 @@ tsubst_template_decl (tree t, tree args, tsubst_flags_t complain,
 bool
 lambda_fn_in_template_p (tree fn)
 {
-  if (!LAMBDA_FUNCTION_P (fn))
+  if (!fn || !LAMBDA_FUNCTION_P (fn))
     return false;
   tree closure = DECL_CONTEXT (fn);
   return CLASSTYPE_TEMPLATE_INFO (closure) != NULL_TREE;
@@ -13248,6 +13240,13 @@ tsubst_arg_types (tree arg_types,
        done in build_over_call.  */
     default_arg = TREE_PURPOSE (arg_types);
 
+    /* Except that we do substitute default arguments under tsubst_lambda_expr,
+       since the new op() won't have any associated template arguments for us
+       to refer to later.  */
+    if (lambda_fn_in_template_p (in_decl))
+      default_arg = tsubst_copy_and_build (default_arg, args, complain, in_decl,
+					   false/*fn*/, false/*constexpr*/);
+
     if (default_arg && TREE_CODE (default_arg) == DEFAULT_ARG)
       {
         /* We've instantiated a template before its default arguments

gcc/testsuite/g++.dg/cpp1y/lambda-defarg7.C

+// PR c++/82053
+// { dg-do compile { target c++14 } }
+
+template<class T>
+int fn() { return 42; }
+
+template<class T>
+auto lam = [](int = fn<T>()){};
+
+int main()
+{
+  lam<int>();
+}