Re: What's cooking in git.git (Jan 2021, #02; Fri, 8)

[David Aguilar <davvid@gmail.com>]

On Fri, Jan 8, 2021 at 11:28 AM Junio C Hamano <gitster@pobox.com> wrote:
>
> * fc/mergetool-automerge (2021-01-06) 5 commits
>  . mergetool: add automerge_enabled tool-specific override function
>  . mergetool: break setup_tool out into separate initialization function
>  . mergetool: add per-tool support for the autoMerge flag
>  . mergetool: alphabetize the mergetool config docs
>  . mergetool: add automerge configuration
>
>  "git mergetool" feeds three versions (base, local and remote) of
>  a conflicted path unmodified.  The command learned to optionally
>  prepare these files with unconflicted parts already resolved.
>
>  Breaks tests on macOS.
>  cf. https://github.com/git/git/runs/1659807735?check_suite_focus=true#step:4:1641


Thank you for seeing these changes through.  It's so close now!

I did some investigation into this issue and narrowed down the root cause.

Here is an example input file called "tiger" for testing the sed
invocations in auto_merge():

$ cat tiger
<<<<<<< HEAD
branch1 both added
=======
tiger both added
>>>>>>> tiger

There are two sed invocations that use \r\? to maybe-match \r for crlf support.
\r\? is not portable to macOS (and freebsd?) sed.

For example, auto_merge() does the equivalent of this in one of the invocations:

    sed -e '/^<<<<<<< /,/^=======\r\?$/d' -e '/^>>>>>>> /d' tiger

It prints nothing on macOS.  "gsed" (gnu-sed) from homebrew prints
"tiger both added". This may affect other unix flavors where sed is
not gnu as well.

To verify I changed the sed invocations in auto_merge() to use gsed
and it's then able to pass the tests.

Fun times in sed portability land.  After a bit of experimentation,
this is what I've managed to whip up:

cr=$(printf '\x0d')
sed -e "/^<<<<<<< /,/^=======$cr\{0,1\}$/d" -e '/^>>>>>>> /d' tiger

- Instead of \r use printf to capture CR into a string so that we can
embed the literal using $cr.
- DQ "..." instead of SQ '...' to allow $cr to be substituted in the string.
- Instead of \? use \{0,1\} which seems to work on both macOS and Linux.

That seems to work and the tests now pass.
If not sed, is there perhaps a perl equivalent for these multi-line
delete-from-X-until-Y expressions that might provide better
portability?

I'll start putting together a patch shortly as this seems to work in
practice.  Let me know if y'all have any sugs or if there are any
portability pitfalls I'm not considering.

cheers,

--
David