Re: Merge conflicts in .gitattributes can cause trouble

[Duy Nguyen <pclouds@gmail.com>]

On Tue, Oct 4, 2016 at 5:19 PM, Lars Schneider <larsxschneider@gmail.com> wrote:
> Hi,
>
>
> If there is a conflict in the .gitattributes during a merge then it looks
> like as if the attributes are not applied (which kind of makes sense as Git
> would not know what to do). As a result Git can treat e.g. binary files
> as text and they can end up with changed line endings in the working tree.
> After resolving the conflict in .gitattributes all files would be marked
> as binary, again, and the user can easily commit the wrongly changed line
> endings.
>
> Consider this script on Windows:
>
> $ git init .
> $ touch first.commit
> $ git add .
> $ git commit -m "first commit"
>
> $ git checkout -b branch
> $ printf "*.bin binary\n" >> .gitattributes
> $ git add .
> $ git commit -m "tracking *.bin files"
>
> $ git checkout master
> $ printf "binary\ndata\n" > file.dat # <-- Unix line ending!
> $ printf "*.dat binary\n" >> .gitattributes # <-- Tell Git to keep Unix line ending!
> $ git add .
> $ git commit -m "tracking *.dat files"
> $ git cat-file -p :file.dat | od -c
> 0000000   b   i   n   a   r   y  \n   d   a   t   a  \n
>                                 ^^^^                ^^^^  <-- Correct!
> $ git checkout branch
> $ git merge master # <-- Causes merge conflict!
> $ printf "*.bin binary\n*.dat binary\n" > .gitattributes # <-- Fix merge conflict!
> $ git add .
> $ git commit -m "merged"
> $ git cat-file -p :file.dat | od -c
> 0000000   b   i   n   a   r   y  \r  \n   d   a   t   a  \r  \n
>                                 ^^^^^^^^                ^^^^^^^^  <-- Wrong!
>
> Possible solutions:
>
> 1. We could print an appropriate warning if we detect a merge conflict
>    in .gitattributes

This is good regardless, to encourage people to resolve conflicts in
.gitattributes first. A good place for this warning may be "git
status"?

> 2. We could disable all line ending conversions in case of a merge conflict
>    (I am not exactly sure about all the implications, though)
>
> 3. We could salvage what we could of the .gitattributes file,
>    perhaps by using the version from HEAD (or more likely, the ours stage of
>    the index) -- suggested by Peff on the related GitHub issue mentioned below

We already have code to fall back to index version in some cases,
adding "fall back on merge conflicts" (and probably updating the index
lookup code too because it looks for stage 0 now) sounds reasonable
(especially with the warning in #1).

BTW whoever fixes this probably should do the same for .gitignore files.
-- 
Duy