PR c++/85214 - ICE with alias, generic lambda, constexpr if.

Here, since the condition for the constexpr if depends on the type of 'j',
it's still dependent when we are partially instantiating the inner lambda,
so we need to defer instantiating the constexpr if.  When we instantiated
the inner lambda, we tried to substitute into the typename, which failed
because we didn't have a declaration of 'i' available.

Fixed by teaching extract_locals_r to capture local typedefs such as 'ar';
if we have the typedef handy, we don't need to substitute into its
definition.

	* pt.c (extract_locals_r): Remember local typedefs.

From-SVN: r259185

gcc/cp/ChangeLog

+2018-04-06  Jason Merrill  <jason@redhat.com>
+
+	PR c++/85214 - ICE with alias, generic lambda, constexpr if.
+	* pt.c (extract_locals_r): Remember local typedefs.
+
 2018-04-06  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c++/84269

gcc/cp/pt.c

@@ -11610,6 +11610,11 @@ extract_locals_r (tree *tp, int */*walk_subtrees*/, void *data_)
   el_data &data = *reinterpret_cast<el_data*>(data_);
   tree *extra = &data.extra;
   tsubst_flags_t complain = data.complain;
+
+  if (TYPE_P (*tp) && typedef_variant_p (*tp))
+    /* Remember local typedefs (85214).  */
+    tp = &TYPE_NAME (*tp);
+
   if (TREE_CODE (*tp) == DECL_EXPR)
     data.internal.add (DECL_EXPR_DECL (*tp));
   else if (tree spec = retrieve_local_specialization (*tp))

gcc/testsuite/g++.dg/cpp1z/constexpr-if20.C

+// PR c++/85214
+// { dg-additional-options -std=c++17 }
+
+struct g {
+  constexpr operator int() { return true; }
+};
+template <typename T, typename U> constexpr bool m = true;
+template <long L> struct C { typedef double q; };
+void ao() {
+  [](auto i) {
+      using ar = typename C<i>::q;
+      [](auto j) {
+	using as = typename C<j>::q;
+	if constexpr (m<ar, as>) {}
+      }(g());
+  }(g());
+}