From 24ec38c7e028723f84ab15ca0ecef6e56a899aea Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 14 Dec 2016 10:03:11 +0200
Subject: Add support for cxx.std=latest, use when building build2

---
 bootstrap-mingw.bat |  3 +++
 bootstrap.sh        |  3 +++
 build/root.build    |  2 +-
 build2/cxx/init.cxx | 48 +++++++++++++++++++++++++++++++++++++++++++-----
 4 files changed, 50 insertions(+), 6 deletions(-)

diff --git a/bootstrap-mingw.bat b/bootstrap-mingw.bat
index 28c7edd..c95d534 100644
--- a/bootstrap-mingw.bat
+++ b/bootstrap-mingw.bat
@@ -76,6 +76,9 @@ set "src=%src% %libbutl%\butl\*.cxx"
 
 rem Get the compile options.
 rem
+rem Note that for as long as we support GCC 4.9 we have to compile in the
+rem C++14 mode since 4.9 doesn't recognize c++1z.
+rem
 set "ops=-std=c++1y"
 :ops_next
 shift
diff --git a/bootstrap.sh b/bootstrap.sh
index 3496a1f..54cc9f2 100755
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -130,5 +130,8 @@ src="$src build2/install/*.cxx"
 src="$src build2/pkgconfig/*.cxx"
 src="$src $libbutl/butl/*.cxx"
 
+# Note that for as long as we support GCC 4.9 we have to compile in the C++14
+# mode since 4.9 doesn't recognize c++1z.
+#
 set -x
 "$cxx" "-I$libbutl" -I. '-DBUILD2_HOST_TRIPLET="'"$host"'"' -std=c++1y "$@" -o build2/b-boot $src -lpthread
diff --git a/build/root.build b/build/root.build
index 1d79e22..517da8b 100644
--- a/build/root.build
+++ b/build/root.build
@@ -2,7 +2,7 @@
 # copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
 # license   : MIT; see accompanying LICENSE file
 
-cxx.std = 14
+cxx.std = latest
 
 using cxx
 
diff --git a/build2/cxx/init.cxx b/build2/cxx/init.cxx
index 61b2c3c..e5641be 100644
--- a/build2/cxx/init.cxx
+++ b/build2/cxx/init.cxx
@@ -42,7 +42,49 @@ namespace build2
     {
       string r;
 
-      if (ci.id.type == "msvc")
+      const string& t (ci.id.type);
+      uint64_t mj (ci.version.major);
+      uint64_t mi (ci.version.minor);
+      uint64_t p (ci.version.patch);
+
+      // Translate "latest" to the compiler/version-appropriate option.
+      //
+      if (v == "latest")
+      {
+        if (t == "msvc")
+        {
+          // VC14u3 and later has /std:c++latest.
+          //
+          if (mj > 19 || (mj == 19 && (mi > 0 || (mi == 0 && p >= 24215))))
+            r = "/std:c++latest";
+        }
+        else if (t == "gcc")
+        {
+          if      (mj >= 5)            r = "-std=c++1z"; // 17
+          else if (mj == 4 && mi >= 8) r = "-std=c++1y"; // 14
+          else if (mj == 4 && mi >= 4) r = "-std=c++0x"; // 11
+        }
+        else if (t == "clang")
+        {
+          if       (mj >  3 || (mj == 3 && mi >= 5)) r = "-std=c++1z"; // 17
+          else if  (mj == 3 && mi >= 4)              r = "-std=c++1y"; // 14
+          else    /* ??? */                          r = "-std=c++0x"; // 11
+        }
+        else if (t == "icc")
+        {
+          if      (mj >= 17)                         r = "-std=c++1z"; // 17
+          else if (mj >  15 || (mj == 15 && p >= 3)) r = "-std=c++1y"; // 14
+          else    /* ??? */                          r = "-std=c++0x"; // 11
+        }
+        else
+          assert (false);
+
+        return r;
+      }
+
+      // Otherwise translate the standard value.
+      //
+      if (t == "msvc")
       {
         // C++ standard-wise, with VC you got what you got up until 14u2.
         // Starting with 14u3 there is now the /std: switch which defaults
@@ -59,10 +101,6 @@ namespace build2
         //
         if (v != "98" && v != "03")
         {
-          uint64_t mj (ci.version.major);
-          uint64_t mi (ci.version.minor);
-          uint64_t p (ci.version.patch);
-
           bool sup (false);
 
           if      (v == "11") // C++11 since VS2010/10.0.
-- 
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