From 4a4c60c51204e3738165028c7dfbc6162e047697 Mon Sep 17 00:00:00 2001
From: Karen Arutyunov <karen@codesynthesis.com>
Date: Thu, 3 Oct 2019 22:00:54 +0300
Subject: Fix testscript regex to be compilable with VC 16.4 preview

---
 libbuild2/test/script/regex.hxx | 34 ++++++++--------------------------
 1 file changed, 8 insertions(+), 26 deletions(-)

diff --git a/libbuild2/test/script/regex.hxx b/libbuild2/test/script/regex.hxx
index faec1fc..1758944 100644
--- a/libbuild2/test/script/regex.hxx
+++ b/libbuild2/test/script/regex.hxx
@@ -197,7 +197,8 @@ namespace build2
           syntax (char);
 
           // Provide basic_regex (such as from msvcrt) with the ability to
-          // explicitly cast line_chars to implementation-specific enums.
+          // explicitly cast line_chars to implementation-specific numeric
+          // types (enums, msvcrt's _Uelem, etc).
           //
           template <typename T>
           explicit
@@ -531,10 +532,12 @@ namespace std
     static const ctype_base::mask _Ch_upper = ctype_base::upper;
     static const ctype_base::mask _Ch_alpha = ctype_base::alpha;
 
-    // Unsigned char_type. msvcrt statically asserts the _Uelem type is
-    // unsigned, so we specialize is_unsigned<line_char> as well (see below).
+    // Unsigned numeric type. msvcrt normally casts characters to this type
+    // for comparing with some numeric values or for calculating an index in
+    // some bit array. Luckily that all relates to the character class
+    // handling that we don't support.
     //
-    using _Uelem = char_type;
+    using _Uelem = unsigned int;
 #endif
 
     regex_traits () = default; // Unnecessary but let's keep for completeness.
@@ -607,7 +610,7 @@ namespace std
   };
 
   // We assume line_char to be an unsigned type and express that with the
-  // following specializations used by basic_regex implementations.
+  // following specialization used by basic_regex implementations.
   //
   // libstdc++ defines unsigned CharT type (regex_traits template parameter)
   // to use as an index in some internal cache regardless if the cache is used
@@ -619,27 +622,6 @@ namespace std
     using type = build2::test::script::regex::line_char;
   };
 
-  // msvcrt assumes regex_traits<line_char>::_Uelem to be present (see above)
-  // and statically asserts it is unsigned.
-  //
-  // And starting from VC 16.1, is_unsigned_v is not implemented in terms of
-  // is_unsigned so we have to get deeper into the implementation details.
-  //
-#if defined(_MSC_VER) && _MSC_VER >= 1921
-  template <>
-  struct _Sign_base<build2::test::script::regex::line_char, false>
-  {
-    static constexpr bool _Signed   = false;
-    static constexpr bool _Unsigned = true;
-  };
-#else
-  template <>
-  struct is_unsigned<build2::test::script::regex::line_char>
-  {
-    static const bool value = true;
-  };
-#endif
-
   // When used with libc++ the linker complains that it can't find
   // __match_any_but_newline<line_char>::__exec() function. The problem is
   // that the function is only specialized for char and wchar_t
-- 
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