Using it:

 (define-key global-map (kbd "C-x C-g") 'git-find-file)

Then 'C-x C-g' from within your project directory. You'll see a list of the files in your current Git repository, and anything you type will be used as input to narrow the list. A pattern like:

 => srcmarcmaclj

Could match files like:

 src/marcgrep/sources/marc_file.clj
 src/marcgrep/sources/marcxml_file.clj
 src/marcgrep/destinations/marcfile.clj

That is, the pattern is applied (very!) fuzzily, and any path where the letters of the pattern appear in order will be returned.

There's some basic relevance ranking here: exact substring matches sort above fuzzy matches, fuzzy matches against the path's basename are better than matches against the entire path, and matches where the letters appear close to one another are better than when they're spread out.

Hitting RET opens the file under point, and C-g will abort the file selection.

Finally, C-s "rotates" the list:

 /path/a              /path/b              /path/c
 /path/b  --[C-s]-->  /path/c  --[C-s]-->  /path/a
 /path/c              /path/a              /path/b