Re: git-diff should not fire up $PAGER if there is no diff

[Jeff King <peff@peff.net>]

On Tue, Dec 16, 2008 at 08:21:33AM +0800, jidanni@jidanni.org wrote:

> git-diff should not fire up $PAGER if there is no diff output.
> Just exit. The man page doesn't even mention $PAGER too.

I agree that would be nice, but it is a little difficult to implement.
The current behavior forks early and then pipes the output to the pager.
So we would have to:

  1. change that behavior to instead delay starting the pager until the
     first output. Which means intercepting every
     write/fwrite/printf/fputs/etc call.

  2. detect EOF before starting the pager. We in fact already delay
     running the pager in the forked process until we have some activity
     on the pipe, but I don't know if there is a portable way of
     detecting that that activity is EOF without performing an actual
     read() call (which is undesirable, since it eats the first byte of
     output that should go to the pager).

  3. a hacky solution to (2) above would be to make _2_ pipes, one of
     which signals to the pager sub-process either "exit now" or "proceed
     with running the pager".

The usual workaround is to ask the pager to exit immediately if the
output is small. I.e., putting "F" in your LESS variable (which git does
automatically if you don't already have LESS set).

-Peff