Back when we added C++11 auto deduction, I thought we could shortcut the
normal deduction in some templates, when the type is adequately
describable (thus the late, unlamented function describable_type). Over
time various problems with this have arisen, of which this is the most
recent; as a result, I'm giving up the attempt as a bad idea and just
deferring auto deduction if the initializer is type-dependent.
Tested x86_64-pc-linux-gnu, applying to trunk.
commit 639eddf82da171a041d5184d5dd2917f102dde3c
Author: Jason Merrill <ja...@redhat.com>
Date: Thu May 31 11:50:20 2012 -0400
PR c++/53484
* pt.c (do_auto_deduction): Don't try to deduce from a
type-dependent initializer.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index c55687b..b58dd13 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -20318,10 +20318,9 @@ do_auto_deduction (tree type, tree init, tree auto_node)
if (init == error_mark_node)
return error_mark_node;
- if (processing_template_decl
- && (TREE_TYPE (init) == NULL_TREE
- || BRACE_ENCLOSED_INITIALIZER_P (init)))
- /* Not enough information to try this yet. */
+ if (type_dependent_expression_p (init))
+ /* Defining a subset of type-dependent expressions that we can deduce
+ from ahead of time isn't worth the trouble. */
return type;
/* [dcl.spec.auto]: Obtain P from T by replacing the occurrences of auto
diff --git a/gcc/testsuite/g++.dg/cpp0x/auto33.C b/gcc/testsuite/g++.dg/cpp0x/auto33.C
new file mode 100644
index 0000000..dade5a8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/auto33.C
@@ -0,0 +1,15 @@
+// PR c++/53484
+// { dg-do compile { target c++11 } }
+
+template<class T,class U> struct ST;
+template<class T> struct ST<T,T> {};
+
+template <class T>
+void f(T x){
+ [&]{
+ auto y = x;
+ ST<decltype(y),int>();
+ }();
+}
+
+int main(){ f(0); }
