[C++ PATCH] Fix ICE with structured binding initialized from lambda in template (PR c++/85209)

[Jakub Jelinek]

Hi!

For cp_finish_decomp we require that the id decl for the structured binding
are chained together, because we pass just the artificial underlying decl
and first id and cp_finish_decomp walks DECL_CHAIN to find other ids.
tsubst_decomp_names was actually requiring not just that, but also that
the artificial undering decl follows the last id, which is unnecessary and
isn't actually true if the initializer has some lambdas in it, because those
might appear in between.

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

2018-04-05  Jakub Jelinek  <ja...@redhat.com>

        PR c++/85209
        * pt.c (tsubst_decomp_names): Don't fail or ICE if DECL_CHAIN (decl3)
        is not prev, if prev == decl.

        * g++.dg/cpp1z/decomp39.C: New test.
        * g++.dg/cpp1z/decomp40.C: New test.

--- gcc/cp/pt.c.jj      2018-04-05 09:49:06.155459292 +0200
+++ gcc/cp/pt.c 2018-04-05 15:02:40.290261785 +0200
@@ -16230,7 +16230,8 @@ tsubst_decomp_names (tree decl, tree pat
       if (error_operand_p (decl3))
        decl = error_mark_node;
       else if (decl != error_mark_node
-              && DECL_CHAIN (decl3) != prev)
+              && DECL_CHAIN (decl3) != prev
+              && decl != prev)
        {
          gcc_assert (errorcount);
          decl = error_mark_node;
--- gcc/testsuite/g++.dg/cpp1z/decomp39.C.jj    2018-04-05 15:10:17.053265429 
+0200
+++ gcc/testsuite/g++.dg/cpp1z/decomp39.C       2018-04-05 15:10:56.099265281 
+0200
@@ -0,0 +1,16 @@
+// PR c++/85209
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+template <int>
+void
+foo ()
+{
+  auto [a] = []{};     // { dg-error "cannot decompose lambda closure type" }
+}                      // { dg-warning "structured bindings only available 
with" "" { target c++14_down } .-1 }
+
+void
+bar ()
+{
+  foo<0> ();
+}
--- gcc/testsuite/g++.dg/cpp1z/decomp40.C.jj    2018-04-05 15:11:58.630265722 
+0200
+++ gcc/testsuite/g++.dg/cpp1z/decomp40.C       2018-04-05 15:11:49.402265657 
+0200
@@ -0,0 +1,18 @@
+// PR c++/85209
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+struct S { int a; } s;
+
+template <int>
+void
+foo ()
+{
+  auto [a] = []{ return s; } ();       // { dg-warning "structured bindings 
only available with" "" { target c++14_down } }
+};
+
+void
+bar ()
+{
+  foo<0> ();
+}

        Jakub