Binary file change by hook not detected due to Git textconv

[adamchainz]

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textconv

describe your issue

I’ve set up Git to use exiftool as a text conversion filter for JPEGs, with this in ~/.config/git/config:

[diff "exiftool"]
    textconv = exiftool --composite -x 'Exiftool:*' -x 'File:*' -g0
    cachetextconv = true
    xfuncname = "^-.*$"

…and this in ~/.config/git/attributes:

*.jpeg diff=exiftool

In my repo, I’m using jpegoptim to optimize JPEG's with the below .pre-commit-config.yaml.

Take an unoptimized JPEG:

$ git status
On branch main
Changes to be committed:
        new file:   donut.jpeg

Running pre-commit, the hook passes:

$ pre-commit run jpegoptim
Optimize JPEGs...........................................................Passed

(There’s no option to make jpegoptim exit with a non-zero status code when it changes files.)

However, the tool did actually modify the image:

$ git status
On branch main
Changes to be committed:
        new file:   donut.jpeg

Changes not staged for commit:
        modified:   donut.jpeg

This behaviour means commits don't include the optimized version of a flie, instead they’re left around unstaged.

pre-commit doesn't detect the change because the text conversions of the binary file before/after are the same, leading to an empty diff:

$ git diff donut.jpeg

But using --no-textconv shows the tool actually made a change:

$ git diff --no-textconv donut.jpeg |cat
diff --git a/donut.jpeg b/donut.jpeg
index 3bd0743..d66a2f4 100644
Binary files a/donut.jpeg and b/donut.jpeg differ

The `git diff` call that pre-commit uses to check for changes, in [`_git_diff()`](https://github.com/pre-commit/pre-commit/blob/e846829992a84ce8066e6513a72a357709eec56c/pre_commit/commands/run.py#L273C6-L277) already uses `--no-ext-diff` to make diffs reproducible
I think it should also use `--no-textconv`.
This would also make it a little faster.

### pre-commit --version

3.0.3 / main

### .pre-commit-config.yaml

```yaml
repos:
-   repo: local
    hooks:
    -   id: jpegoptim
        name: Optimize JPEGs
        entry: jpegoptim
        language: system
        types: [jpeg]

~/.cache/pre-commit/pre-commit.log (if present)

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