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+date = 2021-08-11T16:41:49+02:00
+title = "Better hunk headers with gitattributes(5)"
+
+[taxonomies]
+tags = ["git", "TIL"]
++++
+
+Yesterday whilst catching up on the Git mailing list I stumbled upon this
+[patch](https://public-inbox.org/git/20210810190937.305765-1-tsdh@gnu.org/)
+proposing to improve the hunk header regex for Java. I had never paid much
+attention to how [`git-diff(1)`](https://git-scm.com/docs/git-diff) finds the
+right method signature to show in the headers though I was vaguely aware of a
+bunch of regexes for different languages.
+
+Turns out that by default, as explained in the manual for
+[`gitattributes(5)`](https://git-scm.com/docs/gitattributes#_defining_a_custom_hunk_header),
+`git-diff(1)` emulates the behaviour of GNU `diff -p` and does **not** consult
+any of the language-specific regular expressions. This came as a bit of a
+surprise to me, as Git usually has relatively sane and extensive defaults. Why
+define all these regexes and then not use them by default?
+
+Perhaps one reason is that it is hard to tell when to use which. Git can only
+look at the filename, and not all shell scripts share the `.sh` ending, for
+example. Surely it would not be too invasive, however, to define sensible
+defaults for, say, files ending in `.py` or `.rs`.
+
+In any case I updated my `~/.config/git/attributes` with the following, and am
+now enjoying better hunk headers across the board:
+
+```
+*.c	diff=cpp
+*.cpp	diff=cpp
+*.go	diff=go
+*.md	diff=markdown
+*.pl	diff=perl
+*.py	diff=python
+*.rs	diff=rust
+*.sh	diff=bash
+*.tex	diff=tex
+```
+
+The markdown setting is especially neat since it will now display the nearest
+section right in the diff, like so:
+
+```diff
+--- a/posts/weltschmerz.md
++++ b/posts/weltschmerz.md
+@@ -24,6 +24,10 @@ ## Download
+```