[ccache] Support for color diagnostics

[interfaSys Sàrl]

Hello,

I've just tested the patch with a patched gcc48 with -fdiagnostics-color support 
on FreeBSD 9 and it works with one exception.

GCC's documentations says:
"‘auto’ means to use color only when the standard error is a terminal"

So, if my understanding is correct, this means that, when using 
-fdiagnostics-color=auto , I should be seeing colours when using the 
terminal and indeed, that's the normal behaviour when ccache falls back to 
the compiler (I see colours).

With that patch, I don't see the colours in auto mode. It only works in 
always mode.

Cheers,

Olivier



On Friday, November 29, 2013 12:39:25 PM UTC+1, Lubos Lunak wrote:
>
>
>  Hello, 
>
>  the attached patch adds ccache support for compiler color diagnostics 
> (also 
> reported by somebody as #10075). 
>
>  Clang automatically uses colors for output automatically if used in 
> terminal. 
> Ccache's redirecting to a file disables this. GCC 4.8 has got a similar 
> support, except that it apparently requires also $GCC_COLORS or an 
> explicit 
> option. 
>
>  The patch detects if the compiler would use colors if used without ccache 
> and 
> explicitly forces an option to achieve this. Note that I do not have GCC 
> 4.8 
> here, so I tested with Clang's alias and the GCC_COLORS support is done 
> based 
> on documentation. 
>
> Caveats: 
>
> - GCC developers decided to roll their own name for the option when 
> introducing it. Clang has an alias for the GCC way, but versions predating 
> that obviously can't support it, so it's necessary to detect the compiler. 
> As 
> ccache doesn't do that (and I don't find it worth much effort, as it can't 
> be 
> 100% reliable anyway), the code merely guesses from the binary name. If 
> the 
> compiler used will be e.g. the 'cc' symlink, there'll be no colors. No big 
> deal. 
>
> - Since the stderr is different, obviously compiling with and without 
> colors 
> has different results as well. That means that such a compile 
> is "duplicated". It's hopefully not such a common case, although it's 
> perfectly possible. I don't know if it's worth the effort to try to be 
> smart 
> here. A possibly simple improvement could be to search the cache with and 
> without the option set and if stderr is empty, reuse the result regardless 
> of 
> the option. I'm not quite sure where exactly this should happen in the 
> code. 
>
>  I expect it'd make sense to add $CCACHE_NOCOLORS to disable this support? 
>
>  I can also create manpage section for this color support, but I first 
> wanted 
> to check here with the code. 
>
> -- 
>  Lubos Lunak 
>