[PATCH] tests: drop dependency on `git diff` in check-chainlint

From: Eric Sunshine <sunshine@sunshineco.com>

The "check-chainlint" target runs automatically when running tests and performs self-checks to verify that the chainlinter itself produces the expected output. Originally, the chainlinter was implemented via sed, but the infrastructure has been rewritten in fb41727b7e (t: retire unused chainlint.sed, 2022-09-01) to use a Perl script instead.

The rewrite caused some slight whitespace changes in the output that are ultimately not of much importance. In order to be able to assert that the actual chainlinter errors match our expectations we thus have to ignore whitespace characters when diffing them. As the `-w` flag is not in POSIX we try to use `git diff -w --no-index` before we fall back to non-standard `diff -w -u`.

To accommodate for cases where the host system has no Git installation we use the locally-compiled version of Git. This can result in problems though when the Git project's repository is using extensions that the locally-compiled version of Git doesn't understand, in which case `git` may refuse to run and thus cause the checks to fail.

Work around this issue by normalizing whitespace via sed before invoking diff, which allows any platform diff implementation to be used, thus eliminating the dependency upon `git diff` and the non-POSIX `-w` flag.

Reported-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
---

This is an alternative solution to the issue Patrick's patch[1] addresses. Hopefully, this approach should avoid the sort of push-back Patrick's patch received[2].

I shamelessly stole most of Patrick's commit message.

The sed expressions for normalizing whitespace prior to `diff` may look a bit hairy, but they are simple enough in concept:

* collapse runs of whitespace to a single SP
* drop blank lines (this step is not new)
* fold out possible SP at beginning and end of each line
* fold out SP surrounding common punctuation characters used in shell
  scripts, such as `>`, `|`, `;`, etc.

By the way, I'm somewhat surprised that this issue crops up at all considering that --no-index is being used with git-diff. As such, I would have thought that the local repository's format would not have been interrogated at all. If that's a bug in `git diff --no-index`, then fixing that could be considered yet another alternative solution to the issue raised here.

[1]: https://lore.kernel.org/git/4112adbe467c14a8f22a87ea41aa4705f8760cf6.1702380646.git.ps@pks.im/ [2]: https://lore.kernel.org/git/xmqqr0jqnnmn.fsf@gitster.g/

 t/Makefile | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)