added color support for windows

[Ryuuke]

No description provided.

[vitaut]

Thanks a lot for the PR. A few comments/requests if you don't mind:

• Could you leave the include of windows.h in format.cc and instead of conditionally defining the Color enum, add an array that maps standard ANSI colors to Windows-specific ones? Something like:

  // somewhere in format.cc:
  unsigned char COLORS[] = {
  0,
  FOREGROUND_RED | FOREGROUND_INTENSITY,
  FOREGROUND_GREEN | FOREGROUND_INTENSITY,
  ...
  };
  

• GetStdHandle(STD_OUTPUT_HANDLE) can be called once in print_colored.

• Could you please add checks if the calls to GetStdHandle and SetConsoleTextAttribute succeeded? Something like:

  HANDLE handle = GetStdHandle(STD_OUTPUT_HANDLE);
  if (handle == INVALID_HANDLE_VALUE)
    FMT_THROW(WindowsError(GetLastError(), "cannot get output handle"));
  

• And finally, is there a way to unit test this as it is done for ANSI version in https://github.com/cppformat/cppformat/blob/master/test/format-test.cc#L1373?

[Ryuuke]

Yeah no problem !

[vitaut]

Thanks! This mostly looks good and my only concern now is the use of mutable global state (RESET_COLOR and reset_color_flag) which is not thread-safe. I suggest calling GetConsoleScreenBufferInfo to get the current color unconditionally and getting rid of these global variables.

[Ryuuke]

As you like, In C++11 we could use std::call_once in this case for thread safety, right?

[vitaut]

Yeah, but the library should be compatible with pre-C++11 compilers. Thanks updating the PR.

[vitaut]

I've merged it with minor changes (7004d1e & 9368b6a). However, the PrintColored test is failing: https://ci.appveyor.com/project/vitaut/cppformat/build/1.0.683.

[Ryuuke]

The error in the test is coming from the codes below

  if(!GetConsoleScreenBufferInfo(handle, &infoCon))
    FMT_THROW(GetLastError(), "cannot get console informations");

 if(!SetConsoleTextAttribute(handle, color))
    FMT_THROW(GetLastError(), "cannot set console color");

it seems like it always throws with gtest, but I've tested in a project and it works...

[vitaut]

Looks like the GetStdHandle doesn't work when you redirect the output from a console to a pipe with EXPECT_WRITE. Is there another way to test this, perhaps by accessing the console text directly via the Windows API?

[vitaut]

I've moved the Windows implementation of print_colored to a separate branch, print-colored for now as it needs further testing. I'm happy to look into it myself, but it may take some time.

[vitaut]

@Ryuuke, could you please review the updated CONTIBUTING document, particularly the part about licensing, and let me know if you agree with it being applied to your contributions to {fmt}? The library is likely to be relicensed (#1073) so I'm collecting approval from all earlier contributors. Thanks!

[Ryuuke]

Looks good to me !