Force git diff to use delta?

[devinrhode2]

I'm trying to essentially just call git diff from a node script.. but it's turning out to be very complicated.

Tried: a bunch of different stuff on the node side: sindresorhus/execa#485

[devinrhode2]

I'm thinking this might be a little bit like TTY/color stuff. If you want to force git diff output to include color codes, you can pass in --color.

I don't if git is failing to call delta or if delta is detecting the different environment and opting to fallback to plain git diff output.

[dandavison]

Hi @devinrhode2. git only invokes its pager (that's core.pager or pager.diff etc in git config) if git's output is going to screen (a tty). So that will be why you're not seeing delta being called.

Unfortunately git doesn't seem to have an option like --pager=always. Here are some ways I can think of to do what you want to do:

1. Do the process management yourself in node: start a child git process and a child delta process from node, and send the output from the git process to the input of the delta process.
2. Start a shell process and in it execute something like git diff | delta.
3. It may be possible to trick git (as a child process of your node process) into thinking that it's input is a tty. But I don't know much about that. I do it here in a shell script using something called script that I had never heard of until I googled for how to do it:

   delta/tests/test_navigate_less_history_file

   Lines 32 to 34 in a55f021

   	# Trick git and delta into invoking their pager child processes, despite
   	# output not being a tty.
   	script -q /dev/null git -c pager.log="$DELTA" log -p HEAD~2...HEAD > /dev/null

   But I haven't tried doing that from node.

[dandavison]

While (1) is the most correct/portable, (2)'s probably the easiest to do as a quick proof of principle, i.e. something like

startProcess(['bash', '-c', 'git diff | delta'])

[devinrhode2]

I ended up just breaking up my node script into two stages:

node ./shell-scripts/pre-commit/stage1.mjs;
cat .pre-commit-cache/.git-auto-stage-files-to-diff | PAGER=cat git diff
node ./shell-scripts/pre-commit/stage2.mjs;

This is good for others not using delta too - my goal is to just print the whole diff and keep marching on.

[dandavison]

Cool. (You can do git -P to tell git not to use a pager, FWIW). Is the idea here that your second line created the stage2.mjs output used in the third line? One thing to bear in mind is that delta does make use of the colors in git's output (e.g. for colorMoved and --word-diff), so for full delta functionality you will need git diff --color=always if you are redirecting git's output to file, since otherwise git only outputs color when its output is going to screen.

[dandavison]

since otherwise git only outputs color when its output is going to screen.... but it does output colors to the pager process configured by core.pager. The last two sentences are entirely unclear, I think it may be slightly better explained here: https://github.com/dandavison/delta/blob/master/ARCHITECTURE.md#input

[devinrhode2]

You're too helpful man :)
idk why, I just do not expect quick responses on github
I posted the (hopefully) final piece I'm stuck on here on StackOverflow: https://stackoverflow.com/questions/70284321/why-is-git-diff-cat-file-not-printing-anything
It's very generic issue and, I could give you some points :) 👍

[PatrickF1]

Hi, I wanted to do this as well to integrate my plugin with delta. I asked a question on the git mailing list and got a response (https://lore.kernel.org/git/20230816025715.GB2248431@coredump.intra.peff.net/T/#t). The tldr of their recommendation is to ask users to use interactive.diffFilter, check if it's set, and if so pipe it through that value.