[PATCH v2] help: colorize man pages

Our man pages don't contain many useful colors (just blue links), moreover, many people have groff SGR disabled, so they don't see any colors with man pages.

We can set LESS_TERMCAP variables to render bold and underlined text with colors in the pager; a common trick[1].

Bold is rendered as red, underlined as blue, and standout (messages and highlighted search) as inverse magenta.

This only works when the pager is less.

If the user already has LESS_TERMCAP variables set in his/her environment, those are respected and not overwritten.

A new color configuration is added: `color.man`, otherwise `color.ui` is respected, and in addition color.pager needs to turned on.

Normally check_auto_color() would check the value of `color.pager`, but in this particular case it's not git the one executing the pager, but man. Therefore we need to check pager_use_color ourselves.

[1] https://unix.stackexchange.com/questions/119/colors-in-man-pages/147

Suggested-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Comments-by: Jeff King <peff@peff.net>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
---
Range-diff against v1:
1:  a943dedab8 ! 1:  9e34a49fa9 help: colorize man pages
    @@ Commit message
         Bold is rendered as red, underlined as blue, and standout (messages and
         highlighted search) as inverse magenta.
     
    -    This only works when the pager is less, and the color.pager
    -    configuration is enabled, as well as color.ui.
    +    This only works when the pager is less.
    +
    +    If the user already has LESS_TERMCAP variables set in his/her
    +    environment, those are respected and not overwritten.
    +
    +    A new color configuration is added: `color.man`, otherwise `color.ui` is
    +    respected, and in addition color.pager needs to turned on.
    +
    +    Normally check_auto_color() would check the value of `color.pager`, but
    +    in this particular case it's not git the one executing the pager, but
    +    man. Therefore we need to check pager_use_color ourselves.
     
         [1] https://unix.stackexchange.com/questions/119/colors-in-man-pages/147
     
    +    Suggested-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
    +    Comments-by: Jeff King <peff@peff.net>
         Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
     
    + ## Documentation/config/color.txt ##
    +@@ Documentation/config/color.txt: color.interactive.<slot>::
    + 	or `error`, for four distinct types of normal output from
    + 	interactive commands.
    + 
    ++color.man::
    ++	When set to `always`, always colorize the man pages. When `false`
    ++	(or `never`), never.  When set to `true` or `auto`, use color only
    ++	when the output is written to the terminal. If unset, then the
    ++	value of `color.ui` is used (`auto` by default).
    ++
    + color.pager::
    + 	A boolean to enable/disable colored output when the pager is in
    + 	use (default is true).
    +
      ## builtin/help.c ##
     @@
      #include "config-list.h"
    @@ builtin/help.c
      
      #ifndef DEFAULT_HELP_FORMAT
      #define DEFAULT_HELP_FORMAT "man"
    +@@ builtin/help.c: static int verbose = 1;
    + static unsigned int colopts;
    + static enum help_format help_format = HELP_FORMAT_NONE;
    + static int exclude_guides;
    ++static int man_color = GIT_COLOR_UNKNOWN;
    + static struct option builtin_help_options[] = {
    + 	OPT_BOOL('a', "all", &show_all, N_("print all available commands")),
    + 	OPT_HIDDEN_BOOL(0, "exclude-guides", &exclude_guides, N_("exclude guides")),
     @@ builtin/help.c: static void exec_man_konqueror(const char *path, const char *page)
      	}
      }
      
     +static void colorize_man(void)
     +{
    -+	if (!pager_use_color || !want_color(GIT_COLOR_UNKNOWN))
    ++	if (!want_color(man_color) || !pager_use_color)
     +		return;
     +
     +	/* Disable groff colors */
    @@ builtin/help.c: static void exec_man_man(const char *path, const char *page)
      	execl(SHELL_PATH, SHELL_PATH, "-c", shell_cmd.buf, (char *)NULL);
      	warning(_("failed to exec '%s'"), cmd);
     @@ builtin/help.c: static int git_help_config(const char *var, const char *value, void *cb)
    + 	}
      	if (starts_with(var, "man."))
      		return add_man_viewer_info(var, value);
    ++	if (!strcmp(var, "color.man")) {
    ++		man_color = git_config_colorbool(var, value);
    ++		return 0;
    ++	}
      
     -	return git_default_config(var, value, cb);
     +	return git_color_default_config(var, value, cb);

 Documentation/config/color.txt |  6 ++++++
 builtin/help.c                 | 32 +++++++++++++++++++++++++++++++-
 color.h                        |  1 +
 3 files changed, 38 insertions(+), 1 deletion(-)