RunClang: Provide `__is_assignable` builtin when simulating MSVC >= 1900

Visual Studio 2015 Update 2 (cl 19.00.23918) added an `__is_assignable`
builtin.  It also started using the builtin in the `<type_traits>`
header.  Clang as of version 3.8 does not support this builtin so
CastXML cannot parse it.  Work around this problem by adding our own
implementation of the builtin.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/RunClang.cxx b/src/RunClang.cxx
index 515cf4f..0301388 100644
--- a/src/RunClang.cxx
+++ b/src/RunClang.cxx
@@ -222,6 +222,24 @@ protected:
         }
       }
 
+      // Provide __is_assignable builtin if simulating MSVC.
+      // When a future Clang version supports the builtin then
+      // we can skip this when built against such a Clang.
+      if (CI.getLangOpts().MSCompatibilityVersion >= 190000000 &&
+          CI.getLangOpts().CPlusPlus11) {
+        builtins += "\n"
+          "template <typename T> T&& __castxml__declval() noexcept;\n"
+          "template <typename To, typename Fr, typename =\n"
+          "  decltype(__castxml__declval<To>() = __castxml__declval<Fr>())>\n"
+          "  static char (&__castxml__is_assignable_check(int))[1];\n"
+          "template <typename, typename>\n"
+          "  static char (&__castxml__is_assignable_check(...))[2];\n"
+          "#define __is_assignable(_To,_Fr) \\\n"
+          "  (sizeof(__castxml__is_assignable_check<_To,_Fr>(0)) == \\\n"
+          "   sizeof(char(&)[1]))\n"
+          ;
+      }
+
       // Prevent glibc use of a GNU extension not implemented by Clang.
       if (this->NeedNoMathInlines(this->Opts.Predefines)) {
         builtins += "\n"