Re: [PATCH v2 3/3] diff: let external diffs report that changes are uninteresting

>>> +diff.trustExitCode::
>>> +	If this boolean value is set to true then the `diff.external`
>>> +	command is expected to return exit code 1 if it finds
>>> +	significant changes and 0 if it doesn't, like diff(1).  If it's
>>> +	false then the `diff.external` command is expected to always
>>> +	return exit code 0.  Defaults to false.
>>
>> I find this somewhat unclear. What are the consequences when this value
>> is set to false, but the command exits with code other than 0? Is it
>>
>>     If it's false then any exit code other than 0 of the `diff.external`
>>     command is treated as an error.
>
> Yes, unexpected exit codes are reported as errors.
>
> If trustExitCode is false and --quiet is given then the execution of
> external diffs is skipped, so in that situation there is no exit code to
> expect, though.  Not sure how to express it concisely, though.  This
> attempt looks a bit bloated:
>
> --quiet::
>         Disable all output of the program. Implies `--exit-code`.
>         Disables execution of external diff helpers whose exit code
>         is not trusted, i.e. their respective configuration option
> 	`diff.trustExitCode` or `diff.<driver>.trustExitCode` or
> 	environment variable `GIT_EXTERNAL_DIFF_TRUST_EXIT_CODE` is
> 	false.
>
> Might be worth documenting this original behavior somehow, anyway.  It
> makes sense in hindsight, but surprised me a bit when I wrote the tests.