Add support for gitattributes by WGH- · Pull Request #874 · Wilfred/difftastic

WGH- · 2025-08-29T21:57:34Z

Runs git check-attr to get the files git attributes, and treats the file as binary if the attribute value is "unset", matching the built-in git diff.

Fixes #466

Idea-by: @anuramat (#466 (comment))

WGH- · 2025-08-29T21:58:28Z

This is somewhat quick-and-dirty solution. Perhaps, we we shouldn't run git check-attr so eagerly. In any case, I want to hear some opinions.

Wilfred

Overall the approach here looks totally sensible, thanks for taking the time to write a PR!

I do think it needs a test: perhaps the easiest thing would be to write a unit test that e.g. "package.json\0diff\0unspecified\0" parses to the value you expect, and use that function after getting the raw string from git check-attr.

Otherwise, I think we should support at least the binary attribute too, and this is good to go. Thanks again, and let me know if you need any help :)

src/git.rs

Wilfred · 2026-03-31T21:08:02Z

src/git.rs

+
+/// Corresponds to the diff attribute. See man gitattribute.
+pub(crate) enum DiffAttribute {
+    Set,


Would you mind adding doc comments to these? Even a brief phrase copied from the man page would be a big help. I think Other is something you've added, and isn't defined in git?

Wilfred · 2026-03-31T21:08:36Z

src/git.rs

+            "set" => Self::Set,
+            "unset" => Self::Unset,
+            "unspecified" => Self::Unspecified,
+            _ => Self::Other,


I guess the other option would be to use TryFrom so you don't need this catch-all Other value.

I suppose this is no longer relevant since I changed this variant to Other(String)

Wilfred · 2026-03-31T21:09:58Z

src/git.rs

+            }
+        }
+        Err(err) => {
+            warn!("failed to execute git: {err}");


These should be debug logging I think, especially this one. You can run difft in a directory that isn't a git repository, or even on a machine that doesn't have git installed.

Running git outside of git repository is already handled by output.status.success() check, which gets logged with debug level.

I erroneously claimed that git being unavailable also goes there, but yeah, it actually ends up as a warning here.

Changed it to debug.

Wilfred · 2026-03-31T21:15:19Z

src/git.rs

+/// Runs `git check-attr diff` to get the diff attribute of the path. Returns
+/// [`Option::None`] when either `git` is not available, file is not inside git
+/// directory, or something else went wrong.
+pub(crate) fn check_attr(path: &Path) -> Option<DiffAttribute> {


I think should either be check_diff_attr, or take an attribute name as an argument.

I changed this to check_diff_attr. It also checks binary attribute under the hood, but I decided against complicating thing to the caller too much

src/main.rs

Wilfred · 2026-03-31T21:20:23Z

src/main.rs

    let (mut lhs_src, mut rhs_src) = match (
        guess_content(&lhs_bytes, lhs_path, binary_overrides),
        guess_content(&rhs_bytes, rhs_path, binary_overrides),
+        check_attr(Path::new(display_path)),


This covers the case when someone writes *.ext -diff, but not *.ext binary, which is also mentioned in #466.

Apparently binary means -text -diff -merge according to https://git-scm.com/docs/gitattributes#_using_macro_attributes

I think we should support -text and binary too, and also treat them as forcing binary.

Yeah, that's probably a good idea, since specifying both binary and an external diff driver with diff= is valid.

To avoid calling git check-attr twice, and to hide this complexity in main, I decided to make binary essentially force -diff. Please tell if you're against this implicit behaviour

Alternatively, we could return something like Option<(DiffAttribute, BinaryAttribute)>. That would be more explicit, but the patterm matching expression in main is already complicated as it is, and it will become even more ridiculous.

I don't really have a strong preference here. I can implement it either way, please tell me, how :)

@anuramat

Runs git check-attr to get the files git attributes, and treats the file as binary if the attribute value is "unset", matching the built-in git diff. Fixes Wilfred#466 Idea-by: @anuramat (Wilfred#466 (comment))

WGH- force-pushed the support-gitattributes branch from cd10de9 to 86ef851 Compare March 30, 2026 15:29

Wilfred requested changes Mar 31, 2026

View reviewed changes

WGH- force-pushed the support-gitattributes branch from 86ef851 to 1fcd21d Compare April 1, 2026 20:02

WGH- requested a review from Wilfred April 1, 2026 20:07

WGH- force-pushed the support-gitattributes branch 3 times, most recently from 246876e to a120746 Compare April 2, 2026 18:42

Add support for gitattributes

982edb0

Runs git check-attr to get the files git attributes, and treats the file as binary if the attribute value is "unset", matching the built-in git diff. Fixes Wilfred#466 Idea-by: @anuramat (Wilfred#466 (comment))

WGH- force-pushed the support-gitattributes branch from a120746 to 982edb0 Compare April 2, 2026 18:59

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WGH- commented Aug 29, 2025 •

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