<div dir="ltr">I'm planning to merge this fix into the 4.0 release branch.<div><br></div><div>Although not a regression, since <variant> is a new feature, it would still be nice to ship without this bug.</div><div><br></div><div>I'll merge these changes later today if there are no objections, and once all the bots pass.</div><div><br></div><div>/Eric</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Feb 9, 2017 at 12:01 PM, Eric Fiselier via cfe-commits <span dir="ltr"><<a href="mailto:cfe-commits@lists.llvm.org" target="_blank">cfe-commits@lists.llvm.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: ericwf<br>
Date: Thu Feb  9 13:01:22 2017<br>
New Revision: 294612<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=294612&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-<wbr>project?rev=294612&view=rev</a><br>
Log:<br>
Fix PR31916 - std::visit rejects visitors accepting lvalue arguments<br>
<br>
A static assertion was misfiring since it checked<br>
is_callable<Visitor, decltype(__variant_alt<T>.<wbr>value)>. However<br>
the decltype expression doesn't capture the value category as<br>
required. This patch applies extra braces to decltype to fix<br>
that.<br>
<br>
Modified:<br>
    libcxx/trunk/include/variant<br>
    libcxx/trunk/test/std/<wbr>utilities/variant/variant.<wbr>visit/visit.pass.cpp<br>
<br>
Modified: libcxx/trunk/include/variant<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/variant?rev=294612&r1=294611&r2=294612&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-<wbr>project/libcxx/trunk/include/<wbr>variant?rev=294612&r1=294611&<wbr>r2=294612&view=diff</a><br>
==============================<wbr>==============================<wbr>==================<br>
--- libcxx/trunk/include/variant (original)<br>
+++ libcxx/trunk/include/variant Thu Feb  9 13:01:22 2017<br>
@@ -578,7 +578,7 @@ private:<br>
     constexpr decltype(auto) operator()(_Alts&&... __alts) const {<br>
       __std_visit_exhaustive_<wbr>visitor_check<<br>
           _Visitor,<br>
-          decltype(_VSTD::forward<_Alts><wbr>(__alts).__value)...>();<br>
+          decltype((_VSTD::forward<_<wbr>Alts>(__alts).__value))...>();<br>
       return __invoke_constexpr(_VSTD::<wbr>forward<_Visitor>(__visitor),<br>
                                 _VSTD::forward<_Alts>(__alts).<wbr>__value...);<br>
     }<br>
<br>
Modified: libcxx/trunk/test/std/<wbr>utilities/variant/variant.<wbr>visit/visit.pass.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/libcxx/trunk/test/std/utilities/variant/variant.visit/visit.pass.cpp?rev=294612&r1=294611&r2=294612&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-<wbr>project/libcxx/trunk/test/std/<wbr>utilities/variant/variant.<wbr>visit/visit.pass.cpp?rev=<wbr>294612&r1=294611&r2=294612&<wbr>view=diff</a><br>
==============================<wbr>==============================<wbr>==================<br>
--- libcxx/trunk/test/std/<wbr>utilities/variant/variant.<wbr>visit/visit.pass.cpp (original)<br>
+++ libcxx/trunk/test/std/<wbr>utilities/variant/variant.<wbr>visit/visit.pass.cpp Thu Feb  9 13:01:22 2017<br>
@@ -283,9 +283,20 @@ void test_exceptions() {<br>
 #endif<br>
 }<br>
<br>
+// See <a href="http://llvm.org/PR31916" rel="noreferrer" target="_blank">http://llvm.org/PR31916</a><br>
+void test_caller_accepts_nonconst() {<br>
+  struct A {};<br>
+  struct Visitor {<br>
+    void operator()(A&) {}<br>
+  };<br>
+  std::variant<A> v;<br>
+  std::visit(Visitor{}, v);<br>
+}<br>
+<br>
 int main() {<br>
   test_call_operator_forwarding(<wbr>);<br>
   test_argument_forwarding();<br>
   test_constexpr();<br>
   test_exceptions();<br>
+  test_caller_accepts_nonconst()<wbr>;<br>
 }<br>
<br>
<br>
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</blockquote></div><br></div>