Re: [PATCH 4/8] diff: support reading a file from stdin via "-"

Johannes Schindelin [off-list ref] writes:

This allows you to say

	echo Hello World | git diff x -

to compare the contents of file "x" with the line "Hello World".
This automatically switches to --no-index mode.

Signed-off-by: Johannes Schindelin <redacted>
---

	Since the revision machinery checks for the presence of files,
	diff_populate_filespec() will only change behaviour when there
	is a file "-"... I have yet to think of an elegant fix for that.

Another thing is that at some point diff_populate_filespec()
needs to have a way to discard what was cached if memory
pressure gets tight, and we would want to keep this data read
from the standard input.

One solution would be to add a "const char *stdin_data" to diffopts
and read the data from stdin when you parse the options, and
have populate_filespec point at that with s->data (setting
should_free and should_munmap both to 0).