Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -855,6 +855,44 @@
                         ModuleFiles.end());
 }
 
+static bool parseShowColorsArgs(const ArgList &Args) {
+  // Color diagnostics are the default, unless the terminal doesn't support
+  // them.
+  // Support both clang's -f[no-]color-diagnostics and gcc's
+  // -f[no-]diagnostics-colors[=never|always|auto].
+  enum { Colors_On, Colors_Off, Colors_Auto } ShowColors = Colors_Auto;
+  for (const auto &Arg : Args) {
+    const Option &O = Arg->getOption();
+    if (!O.matches(options::OPT_fcolor_diagnostics) &&
+        !O.matches(options::OPT_fdiagnostics_color) &&
+        !O.matches(options::OPT_fno_color_diagnostics) &&
+        !O.matches(options::OPT_fno_diagnostics_color) &&
+        !O.matches(options::OPT_fdiagnostics_color_EQ))
+      continue;
+
+    if (O.matches(options::OPT_fcolor_diagnostics) ||
+        O.matches(options::OPT_fdiagnostics_color)) {
+      ShowColors = Colors_On;
+    } else if (O.matches(options::OPT_fno_color_diagnostics) ||
+               O.matches(options::OPT_fno_diagnostics_color)) {
+      ShowColors = Colors_Off;
+    } else {
+      assert(O.matches(options::OPT_fdiagnostics_color_EQ));
+      StringRef Value(Arg->getValue());
+      if (Value == "always")
+        ShowColors = Colors_On;
+      else if (Value == "auto")
+        ShowColors = Colors_Auto;
+      else // Value == "never" or any other value
+        ShowColors = Colors_Off;
+    }
+  }
+  if (ShowColors == Colors_On ||
+      (ShowColors == Colors_Auto && llvm::sys::Process::StandardErrHasColors()))
+    return true;
+  return false;
+}
+
 bool clang::ParseDiagnosticArgs(DiagnosticOptions &Opts, ArgList &Args,
                                 DiagnosticsEngine *Diags) {
   using namespace options;
@@ -869,7 +907,7 @@
   Opts.Pedantic = Args.hasArg(OPT_pedantic);
   Opts.PedanticErrors = Args.hasArg(OPT_pedantic_errors);
   Opts.ShowCarets = !Args.hasArg(OPT_fno_caret_diagnostics);
-  Opts.ShowColors = Args.hasArg(OPT_fcolor_diagnostics);
+  Opts.ShowColors = parseShowColorsArgs(Args);
   Opts.ShowColumn = Args.hasFlag(OPT_fshow_column,
                                  OPT_fno_show_column,
                                  /*Default=*/true);