PR c++/90732 - ICE with VLA capture and generic lambda.

We were failing to handle VLA capture in tsubst_lambda_expr; initially
building a DECLTYPE_TYPE for the capture and then tsubsting it doesn't give
the special VLA handling.  So with this patch we call add_capture again for
VLAs.

	* pt.c (tsubst_lambda_expr): Repeat add_capture for VLAs.

gcc/cp/ChangeLog

+2020-01-21  Jason Merrill  <jason@redhat.com>
+
+	PR c++/90732 - ICE with VLA capture and generic lambda.
+	* pt.c (tsubst_lambda_expr): Repeat add_capture for VLAs.
+
 2020-01-21  Iain Sandoe  <iain@sandoe.co.uk>
 	    Bin Cheng  <bin.cheng@linux.alibaba.com>
 

gcc/cp/pt.c

@@ -18751,6 +18751,36 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
        cap = TREE_CHAIN (cap))
     {
       tree ofield = TREE_PURPOSE (cap);
+      tree init = TREE_VALUE (cap);
+      if (PACK_EXPANSION_P (init))
+	init = tsubst_pack_expansion (init, args, complain, in_decl);
+      else
+	init = tsubst_copy_and_build (init, args, complain, in_decl,
+				      /*fn*/false, /*constexpr*/false);
+
+      if (init == error_mark_node)
+	return error_mark_node;
+
+      if (init && TREE_CODE (init) == TREE_LIST)
+	init = build_x_compound_expr_from_list (init, ELK_INIT, complain);
+
+      if (!processing_template_decl
+	  && init && TREE_CODE (init) != TREE_VEC
+	  && variably_modified_type_p (TREE_TYPE (init), NULL_TREE))
+	{
+	  /* For a VLA, simply tsubsting the field type won't work, we need to
+	     go through add_capture again.  XXX do we want to do this for all
+	     captures?  */
+	  tree name = (get_identifier
+		       (IDENTIFIER_POINTER (DECL_NAME (ofield)) + 2));
+	  tree ftype = TREE_TYPE (ofield);
+	  bool by_ref = (TYPE_REF_P (ftype)
+			 || (TREE_CODE (ftype) == DECLTYPE_TYPE
+			     && DECLTYPE_FOR_REF_CAPTURE (ftype)));
+	  add_capture (r, name, init, by_ref, !DECL_NORMAL_CAPTURE_P (ofield));
+	  continue;
+	}
+
       if (PACK_EXPANSION_P (ofield))
 	ofield = PACK_EXPANSION_PATTERN (ofield);
       tree field = tsubst_decl (ofield, args, complain);
@@ -18765,13 +18795,6 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
       if (field == error_mark_node)
 	return error_mark_node;
 
-      tree init = TREE_VALUE (cap);
-      if (PACK_EXPANSION_P (init))
-	init = tsubst_pack_expansion (init, args, complain, in_decl);
-      else
-	init = tsubst_copy_and_build (init, args, complain, in_decl,
-				      /*fn*/false, /*constexpr*/false);
-
       if (TREE_CODE (field) == TREE_VEC)
 	{
 	  int len = TREE_VEC_LENGTH (field);

gcc/testsuite/g++.dg/cpp1y/lambda-vla1.C

+// PR c++/90732
+// { dg-do compile { target c++14 } }
+// { dg-additional-options "-Wno-vla" }
+
+/*const*/ int SIZE = 100;
+
+template<typename T>
+int foo(T t) {
+  char buf[SIZE] = { 24 };
+  return [&buf](auto x){ return buf[x]; }(t);
+}
+
+int main() {
+  if (foo(0) != 24)
+    __builtin_abort();
+}