[GHC] #13444: Disable diagnostic coloring by default

[GHC]

#13444: Disable diagnostic coloring by default
-------------------------------------+-------------------------------------
           Reporter:  hvr            |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:  8.2.1
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Incorrect
  Unknown/Multiple                   |  error/warning at compile-time
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 TO my suprise, GHC 8.2.1 enables colors by default which is rather
 annoying to me as it looks rather ugly with my terminal coloring scheme.
 This should follow GCC's model instead which defaults them off and allows
 to customize the coloring scheme via `GCC_COLORS`. Quoting the GCC man-
 page:


 > `-fdiagnostics-color[=WHEN]`
 > `-fno-diagnostics-color`
 >
 >     Use color in diagnostics.  WHEN is never, always, or auto.  The
 default depends on how
 >     the compiler has been configured, it can be any of the above WHEN
 options or also never
 >     if GCC_COLORS environment variable isn't present in the environment,
 and auto
 >     otherwise.  auto means to use color only when the standard error is
 a terminal.  The
 >     forms -fdiagnostics-color and -fno-diagnostics-color are aliases for
 >     `-fdiagnostics-color=always` and `-fdiagnostics-color=never`,
 respectively.
 >
 >     The colors are defined by the environment variable `GCC_COLORS`.
 Its value is a colon-
 >     separated list of capabilities and Select Graphic Rendition (SGR)
 substrings. SGR
 >     commands are interpreted by the terminal or terminal emulator.  (See
 the section in the
 >     documentation of your text terminal for permitted values and their
 meanings as
 >     character attributes.)  These substring values are integers in
 decimal representation
 >     and can be concatenated with semicolons.  Common values to
 concatenate include 1 for
 >     bold, 4 for underline, 5 for blink, 7 for inverse, 39 for default
 foreground color, 30
 >     to 37 for foreground colors, 90 to 97 for 16-color mode foreground
 colors, 38;5;0 to
 >     38;5;255 for 88-color and 256-color modes foreground colors, 49 for
 default background
 >     color, 40 to 47 for background colors, 100 to 107 for 16-color mode
 background colors,
 >     and 48;5;0 to 48;5;255 for 88-color and 256-color modes background
 colors.
 >
 >     The default `GCC_COLORS` is
 >
 >
 `error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01`
 >
 >     where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan,
 01;32 is bold green
 >     and 01 is bold. Setting GCC_COLORS to the empty string disables
 colors.  Supported
 >     capabilities are as follows.
 >
 >     "error="
 >         SGR substring for error: markers.
 >
 >     "warning="
 >         SGR substring for warning: markers.
 >
 >     "note="
 >         SGR substring for note: markers.
 >
 >     "caret="
 >         SGR substring for caret line.
 >
 >     "locus="
 >         SGR substring for location information, file:line or
 file:line:column etc.
 >
 >     "quote="
 >         SGR substring for information printed within quotes.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13444>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler