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Re: [PATCH v2] doc-diff: don't `cd_to_toplevel` before calling `usage`

On Sun, Feb 03, 2019 at 12:08:17PM +0100, Martin Ågren wrote:

> `usage` tries to call $0, which might very well be "./doc-diff", so if
> we `cd_to_toplevel` before calling `usage`, we'll end with an error to
> the effect of "./doc-diff: not found" rather than a friendly `doc-diff
> -h` output. Granted, all of these `usage` calls are in error paths, so
> we're about to exit anyway, but the user experience of something like
> `(cd Documentation && ./doc-diff)` could be a bit better than
> "./doc-diff: not found".
> This regressed in ad51743007 ("doc-diff: add --clean mode to remove
> temporary working gunk", 2018-08-31) where we moved the call to
> `cd_to_toplevel` to much earlier. Move it back to where it was, and
> teach the "--clean" code to cd on its own. This way, we only cd once
> we've verified the arguments.
> A more general fix would be to teach git-sh-setup to save away the
> absolute path for $0 and then use that, instead. I'm not aware of any
> portable way of doing that, see, e.g., d2addc3b96 ("t7800: readlink
> may not be available", 2016-05-31), so let's just fix this user
> instead.

This (and the patch) seems quite reasonable as a fix.

I actually think we could go further and drop the cd_to_toplevel
entirely. IIRC, the only thing it accomplishes[1] is that we can
consistently refer to the tmp directory as Documentation/tmp-doc-diff.

It would probably be fine to:

  - use "$(git rev-parse --show-toplevel)/Documentation/tmp-doc-diff".
    In earlier iterations of the script, I think using an absolute path
    bled through to the resulting diff, but we later cleaned that up

  - just use a relative "tmp-doc-diff". I doubt anybody actually wants
    to do anything other than "cd Documentation && ./doc-diff" anyway.
    This breaks "./Documentation/doc-diff", but it is not like you can
    run "t/t0000-basic.sh" either.


[1] I think also in early iterations I had some notion of using the cwd
    to build things, but that quickly went out the window in favor of