[raw_ostream] When printing color on Windows, use the existing foreground / background color.

[zturner]

Summary

According to MSDN [https://msdn.microsoft.com/en-us/library/windows/desktop/ms682088(v=vs.85).aspx#_win32_character_attributes], when setting the console attribute, whichever property you don't set has a default value chosen.

Quote: "If no background constant is specified, the background is black, and if no foreground constant is specified, the text is black"

This is annoying if you have changed the default background color of your console and then use raw_ostrema to change the foreground color (or vice versa), because setting only the foreground attribute will also choose a default value for the background which will be different than your current console's setting.

This patch gets the current value of both attributes, and when you set one attribute, it sets the opposite attribute to its existing value before committing the color update.

[zturner]

Fixed a variable shadowing and removed unnecessary locals.

[aaron.ballman]

LGTM, thank you for doing this!

~Aaron

llvm/trunk/lib/Support/Windows/Process.inc

static unsigned GetCurrentColor() {
       if (GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &csbi))
         return csbi.wAttributes;
       return 0;
     }
     WORD operator()() const { return defaultColor; }
 };
 
 DefaultColors defaultColors;
+
+WORD fg_color(WORD color) {
+  return color & (FOREGROUND_BLUE | FOREGROUND_GREEN |
+                  FOREGROUND_INTENSITY | FOREGROUND_RED);
+}
+
+WORD bg_color(WORD color) {
+  return color & (BACKGROUND_BLUE | BACKGROUND_GREEN |
+                  BACKGROUND_INTENSITY | BACKGROUND_RED);
+}
 }
 
 bool Process::ColorNeedsFlush() {
   return !UseANSI;
 }
 
 const char *Process::OutputBold(bool bg) {
   if (UseANSI) return "\033[1m";
 
   WORD colors = DefaultColors::GetCurrentColor();
   if (bg)
     colors |= BACKGROUND_INTENSITY;
   else
     colors |= FOREGROUND_INTENSITY;
   SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), colors);
   return 0;
 }
 
 const char *Process::OutputColor(char code, bool bold, bool bg) {
   if (UseANSI) return colorcodes[bg?1:0][bold?1:0][code&7];
 
+  WORD current = DefaultColors::GetCurrentColor();
   WORD colors;
   if (bg) {
     colors = ((code&1) ? BACKGROUND_RED : 0) |
       ((code&2) ? BACKGROUND_GREEN : 0 ) |
       ((code&4) ? BACKGROUND_BLUE : 0);
     if (bold)
       colors |= BACKGROUND_INTENSITY;
+    colors |= fg_color(current);
   } else {
     colors = ((code&1) ? FOREGROUND_RED : 0) |
       ((code&2) ? FOREGROUND_GREEN : 0 ) |
       ((code&4) ? FOREGROUND_BLUE : 0);
     if (bold)
       colors |= FOREGROUND_INTENSITY;
+    colors |= bg_color(current);
   }
   SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), colors);
   return 0;
 }
 
 static WORD GetConsoleTextAttribute(HANDLE hConsoleOutput) {
   CONSOLE_SCREEN_BUFFER_INFO info;
   GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &info);