[C++ PATCH] Fix ICE with structured binding & to incomplete type (PR c++/83217)

[Jakub Jelinek]

Hi!

When the structured binding decl doesn't have a reference type,
cp_finish_decl makes sure its type is complete, but if it has
a reference type, that doesn't happen and we ICE trying to
access bases of a not yet instantiated type.

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,
ok for trunk?

2017-11-30  Jakub Jelinek  <ja...@redhat.com>

        PR c++/83217
        * decl.c (cp_finish_decomp): If decl's type is REFERENCE_TYPE,
        call complete_type (TREE_TYPE (type)).

        * g++.dg/cpp1z/decomp33.C: New test.

--- gcc/cp/decl.c.jj    2017-11-30 11:18:00.000000000 +0100
+++ gcc/cp/decl.c       2017-11-30 15:34:55.873673157 +0100
@@ -7424,7 +7424,9 @@ cp_finish_decomp (tree decl, tree first,
   if (TREE_CODE (type) == REFERENCE_TYPE)
     {
       dexp = convert_from_reference (dexp);
-      type = TREE_TYPE (type);
+      type = complete_type (TREE_TYPE (type));
+      if (type == error_mark_node)
+       goto error_out;
     }
 
   tree eltype = NULL_TREE;
--- gcc/testsuite/g++.dg/cpp1z/decomp33.C.jj    2017-11-30 15:37:58.781405774 
+0100
+++ gcc/testsuite/g++.dg/cpp1z/decomp33.C       2017-11-30 15:38:28.006043496 
+0100
@@ -0,0 +1,21 @@
+// PR c++/83217
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+template <typename T>
+struct S
+{
+  T a;
+};
+
+void
+foo (S<int> *b)
+{
+  auto & [c] = *b;     // { dg-warning "structured bindings only available 
with" "" { target c++14_down } }
+}
+
+void
+bar (S<char> *d)
+{
+  auto [e] = *d;       // { dg-warning "structured bindings only available 
with" "" { target c++14_down } }
+}

        Jakub