search

martinvonz / jj

A Git-compatible VCS that is both simple and powerful
https://martinvonz.github.io/jj/
Apache License 2.0
7.24k stars 240 forks source link

FR: Materialize files with conflict markers (or any files) in a way that can be parsed #3975

Open ilyagr opened 6 days ago

ilyagr commented 6 days ago

This is a tracking issue for this bug/FR. I'm promoting this discussion from https://github.com/martinvonz/jj/issues/3968#issuecomment-2192516971. I think I also have a plan now that could work, so I am posting an outline it here in case people have comments.

The alternative would be to declare that it is not a goal to be able to materialize any text file conflict, and show a materialization error instead. I was leaning towards this, but I think the following approach is simple enough to work.

Originally posted by @ilyagr in https://github.com/martinvonz/jj/issues/3968#issuecomment-2192516971

Wouldn't you want to preserve the invariant that you can reconstruct any of the file sides directly from the conflicted contents, rather than having to consult an out-of-band store?

This issue has been nerd-sniping me for a while; in addition to trailing newlines (Update: in non-empty files; we actually support files that are 0 or more lines, each ending with a newline), it's also a matter of encoding conflict markers inside files

TODO: find link. I remember discussing it with Martin recently in some PR, haven't found it yet. TLDR: jj currently can't handle conflicts in out own tutorial.md because of

https://github.com/martinvonz/jj/blob/638649b435795bbb991d840e9ad1750648d9b74a/docs/tutorial.md?plain=1#L284-L291

In the shortest term, I'll probably ignore both issues and just add newlines to the end of files.

However, I think I finally figured out a syntax that will work, will not require a complicated parser, and even be somewhat readable. Before computing conflicts (and only if a file is conflicted), we'd encode file contents as follows:

  1. A mildly pathological file
JJ Verbatim Line:<<<<<<<<<<<
blahblah
JJ EOF: No newline at the end of file
  1. A moderately pathological file
JJ Verbatim Line:<<<<<<<<<<<
JJ Verbatim Line:JJ Verbatim Line:<<<<<<<<<<<
blahblah
JJ Verbatim Line:JJ EOF: No newline at the end of file
  1. Another fun file
blah
JJ Verbatim Line:JJ EOF: No newline at the end of file
JJ EOF: No newline at the end of file

Fun, huh?

This relies on conflict markers having to start at the beginning of the line. If we ever have a notion of conflicts that happen in the middle of lines, we'd need a different syntax, of course. I think that would be nice, but also would probably need a whole different UI to be usable; I'm not sure it can be very usable in the terminal or as a text file.

ilyagr commented 6 days ago

TODO: Check if there are problems with diffing non-empty files that don't end in a newline.

If we do JJ EOF: No newline at the end of file for conflicts, it would be nice to do it for diffs as well, but that's a slightly separate issue.