On Tue, Sep 3, 2013 at 9:41 AM, Jeff King <p...@peff.net> wrote:
> On Mon, Sep 02, 2013 at 10:27:48PM -0400, Dale R. Worley wrote:
>> > I guess the "else" could and should be dropped. If you do so (and
>> > possibly insert a blank line between the DEFAULT_PAGER case and the
>> > "pager = NULL" case), you get a nice pattern
>> >
>> > if (!pager)
>> >     try_something();
>> > if (!pager)
>> >     try_next_option();
>> That's true, but it would change the effect of using "cat" as a value:
>> "cat" as a value of DEFAULT_PAGER would cause git_pager() to return
>> NULL, whereas now it causes git_pager() to return "cat".  (All other
>> places where "cat" can be a value are translated to NULL already.)
>> This is why I want to know what the *intended* behavior is, because we
>> might be changing Git's behavior, and I want to know that if we do
>> that, we're changing it to what it should be.  And I haven't seen
>> anyone venture an opinion on what the intended behavior is.
> I'll venture my opinion. We should do this:
> -- >8 --
> Subject: pager: turn on "cat" optimization for DEFAULT_PAGER
> If the user specifies a pager of "cat" (or the empty
> string), whether it is in the environment or from config, we
> automagically optimize it out to mean "no pager" and avoid
> forking at all. We treat an empty pager variable similary.
> However, we did not apply this optimization when
> DEFAULT_PAGER was set to "cat" (or the empty string). There
> is no reason to treat DEFAULT_PAGER any differently. The
> optimization should not be user-visible (unless the user has
> a bizarre "cat" in their PATH). And even if it is, we are
> better off behaving consistently between the compile-time
> default and the environment and config settings.
> The stray "else" we are removing from this code was
> introduced by 402461a (pager: do not fork a pager if PAGER
> is set to empty., 2006-04-16). At that time, the line
> directly above used:
>    if (!pager)
>            pager = "less";
> as a fallback, meaning that it could not possibly trigger
> the optimization. Later, a3d023d (Provide a build time
> default-pager setting, 2009-10-30) turned that constant into
> a build-time setting which could be anything, but didn't
> loosen the "else" to let DEFAULT_PAGER use the optimization.
> Noticed-by: Dale R. Worley <wor...@alum.mit.edu>
> Suggested-by: Matthieu Moy <matthieu....@grenoble-inp.fr>
> Signed-off-by: Jeff King <p...@peff.net>
> ---
>  pager.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> diff --git a/pager.c b/pager.c
> index c1ecf65..fa19765 100644
> --- a/pager.c
> +++ b/pager.c
> @@ -54,7 +54,7 @@ const char *git_pager(int stdout_is_tty)
>                 pager = getenv("PAGER");
>         if (!pager)
>                 pager = DEFAULT_PAGER;
> -       else if (!*pager || !strcmp(pager, "cat"))
> +       if (!*pager || !strcmp(pager, "cat"))

Hmmpf. It's sometimes useful to actually pipe through cat rather than
disabling the pager, as this changes the return-code from isatty. I
sometimes use this for debugging-purposes. Does this patch break that?
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