Re: [PATCH] convert: fail gracefully upon missing clean cmd on required filter

Matheus Tavares [off-list ref] writes:

The gitattributes documentation mentions that either the clean cmd or
the smudge cmd can be left unspecified in a filter definition. However,
when the filter is marked as 'required', the absence of any one of these
two should be treated as an error. Git already fails under these
circumstances, but not always in a pleasant way: omitting a clean cmd in
a required filter triggers an assertion error which leaves the user with
a quite verbose message:

git: convert.c:1462: convert_to_git_filter_fd: Assertion "ca.drv->clean || ca.drv->process" failed.

This assertion and the one above it are not really necessary, as the
apply_filter() call bellow them already performs the same checks. And
when these conditions are not met, the function returns 0, making the
caller die() with a much nicer message. (Also note that die()-ing here
is the right behavior as `would_convert_to_git_filter_fd() == true` is a
precondition to use convert_to_git_filter_fd(), and the former is only
true when the filter is required.) So remove both assertions and add two
regression tests to make sure that git fails nicely when either the
smudge or clean command is missing on a required filter.

Makes sense.

Will queue, thanks.