A commit that moves an entire package elsewhere renames hundreds of
files, and passing every one of their old paths can push the command past
the length limit the OS imposes (~32k characters on Windows). Their
common parent directory does just as well whenever everything it holds
ends up in the diff anyway.
Deciding that needs to consider every file of the diff, not only those on
display, so the paths are now derived from the model rather than from the
tree; a status filter must not make a directory look emptier than it is.
Git limits its tree diff by the pathspec before it looks for renames, so
a directory only ever gets one end of a rename whose other end is outside
it. Nothing is left to pair up, and the file turns into an addition or a
deletion that the commit doesn't contain.
Pass the other end along with the directory. This is bounded by the
number of renames that cross the directory's boundary, so it costs
nothing at all for the vast majority of commits.
Stefan Haller