[0/3] diff --no-index: support reading from named pipes

Message

Phillip Wood June 27, 2023, 2:10 p.m. UTC

From: Phillip Wood <[e-mail]>

In some shells, such as bash and zsh, it's possible to use a command
substitution to provide the output of a command as a file argument to
another process, like so:

  diff -u <(printf "a\nb\n") <(printf "a\nc\n")

However, this syntax does not produce useful results with git diff
--no-index. On macOS, the arguments to the command are named pipes
under /dev/fd, and git diff doesn't know how to handle a named
pipe. On Linux, the arguments are symlinks to pipes, so git diff
"helpfully" diffs these symlinks, comparing their targets like
"pipe:[1234]" and "pipe:[5678]".

There have been at least three previous attempts [1-3] to address this
issue. They all seem to have received broad support for the aim of
supporting process substitutions but have foundered on details of the
implementation. In an effort to avoid the same fate this series is
narrowly focussed on making command substitutions work with "diff
--no-index" and does not attempt to add a general facility for
de-referencing symbolic links or reading from pipes to the diff
machinery.

The only functional change is that if a path given on the commandline
is a named pipe or a symbolic link that resolves to a named pipe then
we read the data to diff from that pipe. The first two patches improve
the error handling when reading from stdin and add a test. The third
patch implements support for reading from pipes.

This cover letter and the commit message for the third patch are
largely copied from brian’s patch[2] - do we have a standard commit
trailer for "I stole the commit message from someone else's patch"?

I've cc’d the participants of the discussion of the last attempt[1] to
fix this.

[1] https://lore.kernel.org/git/[e-mail]/
[2] https://lore.kernel.org/git/[e-mail]/
[3] https://public-inbox.org/git/[e-mail]/


Base-Commit: 94486b6763c29144c60932829a65fec0597e17b3
Published-As: https://github.com/phillipwood/git/releases/tag/diff-no-index-pipes%2Fv1
View-Changes-At: https://github.com/phillipwood/git/compare/94486b676...990e71882
Fetch-It-Via: git fetch https://github.com/phillipwood/git diff-no-index-pipes/v1

Phillip Wood (3):
  diff --no-index: die on error reading stdin
  t4054: test diff --no-index with stdin
  diff --no-index: support reading from named pipes

 diff-no-index.c          | 83 ++++++++++++++++++++++++----------------
 t/t4053-diff-no-index.sh | 43 +++++++++++++++++++++
 2 files changed, 92 insertions(+), 34 deletions(-)