Resolve follows sybmolic link and mangles submodule pathing

[kangasp]

This is an edge case I had the painful pleasure of finding today.
If there is a submodule at the same depth in the project, as the super project is to a matching symlink, then the pathing to the submodule can break.

Example setup:

Super project home:

• /home/user/git_things/my_project/src_repo

Add a submodule to the project at a path that matches a symlink in the system at the right depth:

• /home/user/git_things/my_project/src_repo/lib/utl/helpers

Make sure you have a matching symlink:

ls -alh /home/user/git_things/my_project/src_repo/../../../../../lib
/home/user/git_things/my_project/src_repo/../../../../../lib -> usr/lib

If all these conditions are met, then fugitive.vim:: s:Tree() will use resolve on the worktree and corrupt it. Something like this:
'../../../../../lib/utl/helpers' --> '../../../../../usr/lib/utl/helpers'
And then, sad sad, no more nice git blame windows for that submodule.

This is on a Linux WSL2 system.
Sorry no patch. I don't feel familiar enough with what could break by messing with the resolve cmd.

Relates to: #2397

[tpope]

If all these conditions are met, then fugitive.vim:: s:Tree() will use resolve on the worktree and corrupt it.

I think what needs to happen here is if worktree is relative, it needs to be prepended with dir . '/' before feeding it to resolve():

diff --git i/plugin/fugitive.vim w/plugin/fugitive.vim
index 86e65767..e63f897c 100644
--- i/plugin/fugitive.vim
+++ w/plugin/fugitive.vim
@@ -374,6 +374,9 @@ function! s:Tree(path) abort
       endif
     endif
     if exists('worktree')
+      if worktree !~# '^/\|^\a:'
+        let worktree = dir . '/' . worktree
+      endif
       let s:worktree_for_dir[dir] = s:Slash(resolve(worktree))
       let s:dir_for_worktree[s:worktree_for_dir[dir]] = dir
     endif

If you can confirm that works I'll ship it.

[it3q]

I had a similar issue (:Git command uses improper root directory under a submodule). Adding these three lines fixes this in my case. Thank you!