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

From: Phillip Wood <phillip.wood@dunelm.org.uk>

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/20200918113256.8699-3-tguyot@gmail.com/ [2] https://lore.kernel.org/git/20181220002610.43832-1-sandals@crustytoothpaste.net/ [3] https://public-inbox.org/git/20170113102021.6054-1-dennis@kaarsemaker.net/

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(-)