[llvm] r342588 - Workaround a limitation of llvm::Any when used with types that have

[Chandler Carruth via llvm-commits]

Author: chandlerc
Date: Wed Sep 19 13:45:09 2018
New Revision: 342588

URL: http://llvm.org/viewvc/llvm-project?rev=342588&view=rev
Log:
Workaround a limitation of llvm::Any when used with types that have
a converting constructor from llvm::Any like gmock matchers. This issue
has come up elsewhere as well and the workaround here is being
considered for use in the standard long-term, but we can pretty cheaply
experiment with it to see if anything ends up going wrong.

Modified:
    llvm/trunk/include/llvm/ADT/Any.h

Modified: llvm/trunk/include/llvm/ADT/Any.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/Any.h?rev=342588&r1=342587&r2=342588&view=diff
==============================================================================
--- llvm/trunk/include/llvm/ADT/Any.h (original)
+++ llvm/trunk/include/llvm/ADT/Any.h Wed Sep 19 13:45:09 2018
@@ -65,6 +65,16 @@ public:
       typename std::enable_if<
           llvm::conjunction<
               llvm::negation<std::is_same<typename std::decay<T>::type, Any>>,
+              // We also disable this overload when an `Any` object can be
+              // converted to the parameter type because in that case, this
+              // constructor may combine with that conversion during overload
+              // resolution for determining copy constructibility, and then
+              // when we try to determine copy constructibility below we may
+              // infinitely recurse. This is being evaluated by the standards
+              // committee as a potential DR in `std::any` as well, but we're
+              // going ahead and adopting it to work-around usage of `Any` with
+              // types that need to be implicitly convertible from an `Any`.
+              llvm::negation<std::is_convertible<Any, typename std::decay<T>::type>>,
               std::is_copy_constructible<typename std::decay<T>::type>>::value,
           int>::type = 0>
   Any(T &&Value) {