Add diagnostics color support on Windows (GH issue #312)

Note that currently this has to be enabled with an explicit --diag-color
option. In the future the plan is to enable it by default if supported.

3 files changed, 66 insertions, 27 deletions

diff --git a/libbuild2/cc/common.cxx b/libbuild2/cc/common.cxx
index 07a4d48..2f428c3 100644
--- a/libbuild2/cc/common.cxx
+++ b/libbuild2/cc/common.cxx
@@ -1618,9 +1618,35 @@ namespace build2
       {
       case compiler_class::msvc:
         {
-          // Note: see init_diag logic if enabling anything here (probably
-          // need an "override disable" mode or some such).
+          // MSVC has the /diagnostics: option which has an undocumented value
+          // `color`. It's unclear from which version of MSVC this value is
+          // supported, but it works in 17.0, so let's start from there.
           //
+          // Note that there is currently no way to disable color in the MSVC
+          // diagnostics specifically (the /diagnostics:* option values are
+          // cumulative and there doesn't seem to be a `color-` value). This
+          // is probably not a big deal since one can just disable the color
+          // globally (--no-diag-color).
+          //
+          // Note that clang-cl appears to use -fansi-escape-codes. See GH
+          // issue #312 for background.
+          //
+          if (show_diag_color ())
+          {
+            if (cvariant.empty () &&
+                (cmaj > 19 || (cmaj == 19 && cmin >= 30)))
+            {
+              // Check for the prefix in case /diagnostics:color- gets added
+              // eventually.
+              //
+              if (!find_option_prefixes ({"/diagnostics:color",
+                                          "-diagnostics:color"}, args))
+              {
+                args.push_back ("/diagnostics:color");
+              }
+            }
+          }
+
           break;
         }
       case compiler_class::gcc:
@@ -1628,13 +1654,18 @@ namespace build2
           // Enable/disable diagnostics color unless a custom option is
           // specified.
           //
-          // Supported from GCC 4.9 and (at least) from Clang 3.5. Clang
-          // supports -f[no]color-diagnostics in addition to the GCC's
-          // spelling.
+          // Supported from GCC 4.9 (8.1 on Windows) and (at least) from Clang
+          // 3.5. Clang supports -f[no]color-diagnostics in addition to the
+          // GCC's spelling.
           //
-          if (ctype == compiler_type::gcc   ? cmaj > 4 || (cmaj == 4 && cmin >= 9) :
-              ctype == compiler_type::clang ? cmaj > 3 || (cmaj == 3 && cmin >= 5) :
-              false)
+          if (
+#ifndef _WIN32
+            ctype == compiler_type::gcc   ? cmaj > 4 || (cmaj == 4 && cmin >= 9) :
+#else
+            ctype == compiler_type::gcc   ? cmaj > 8 || (cmaj == 8 && cmin >= 1) :
+#endif
+            ctype == compiler_type::clang ? cmaj > 3 || (cmaj == 3 && cmin >= 5) :
+            false)
           {
             if (!(find_option_prefix ("-fdiagnostics-color", args)        ||
                   find_option        ("-fno-diagnostics-color", args)     ||
diff --git a/libbuild2/diagnostics.cxx b/libbuild2/diagnostics.cxx
index e164f10..4a46756 100644
--- a/libbuild2/diagnostics.cxx
+++ b/libbuild2/diagnostics.cxx
@@ -3,9 +3,10 @@
 
 #include <libbuild2/diagnostics.hxx>
 
-#include <cstring> // strcmp(), strchr(), memcpy()
+#include <cstring> // strchr(), memcpy()
 #include <cstdlib> // getenv()
 
+#include <libbutl/fdstream.hxx>   // fdterm_color()
 #include <libbutl/process-io.hxx>
 
 #include <libbuild2/scope.hxx>
@@ -30,7 +31,7 @@ namespace build2
   bool diag_no_line = false;
   bool diag_no_column = false;
 
-  optional<const char*> stderr_term = nullopt;
+  bool stderr_term = false;
   bool stderr_term_color = false;
 
   void
@@ -50,29 +51,38 @@ namespace build2
     diag_color_option = c;
     diag_no_line = nl;
     diag_no_column = nc;
+    stderr_term = st;
 
     if (st)
     {
-      stderr_term = std::getenv ("TERM");
-
-      stderr_term_color =
+      // @@ TMP: eventually we want to enable on Windows by default.
+      //
 #ifdef _WIN32
-        // For now we disable color on Windows since it's unclear if/where/how
-        // it is supported. Maybe one day someone will figure this out.
+      if (c && *c)
+      {
+#endif
+        stderr_term_color = fdterm_color (stderr_fd (), !c || *c /* enable */);
+
+        // If the user specified --diag-color on POSIX we will trust the color
+        // is supported (e.g., wrong TERM value, etc).
         //
-        false
+        if (!stderr_term_color && c && *c)
+        {
+#ifdef _WIN32
+          fail << "unable to enable diagnostics color support for stderr";
 #else
-        // This test was lifted from GCC (Emacs shell sets TERM=dumb).
-        //
-        *stderr_term != nullptr && strcmp (*stderr_term, "dumb") != 0
+          stderr_term_color = true;
+#endif
+        }
+
+#ifdef _WIN32
+      }
+      else
+        stderr_term_color = false;
 #endif
-        ;
     }
     else
-    {
-      stderr_term = nullopt;
       stderr_term_color = false;
-    }
   }
 
   // Stream verbosity.
diff --git a/libbuild2/utility.hxx b/libbuild2/utility.hxx
index 43cb904..f37fc54 100644
--- a/libbuild2/utility.hxx
+++ b/libbuild2/utility.hxx
@@ -149,11 +149,9 @@ namespace build2
   LIBBUILD2_SYMEXPORT extern bool diag_no_line;   // --no-line
   LIBBUILD2_SYMEXPORT extern bool diag_no_column; // --no-column
 
-  // If stderr is not a terminal, then the value is absent (so can be used as
-  // bool). Otherwise, it is the value of the TERM environment variable (which
-  // can be NULL).
+  // True if stderr is a terminal.
   //
-  LIBBUILD2_SYMEXPORT extern optional<const char*> stderr_term;
+  LIBBUILD2_SYMEXPORT extern bool stderr_term;
 
   // True if the color can be used on the stderr terminal.
   //