Requirements

Trigger (automatic):

• open any file
• open any directory
• open any file pattern
• open any directory pattern

or run only when invoked

Root directory:

• contains a known file (e.g. Rakefile)
• contains a known directory (e.g. .git/)
• contains a known symlink directory (e.g. foo/ -> /some/path/)
• contains a known symlink file (e.g. bar.txt -> /some/file.txt)
• contains a file matching a pattern (e.g. *.sln)
• contains a directory matching a pattern ?
• contains a known subdirectory file (e.g. build/envset-up.sh)
• is a known directory (e.g. foobar/)

Search:

• first match (depth-first)
• nearest match (breadth-first)

No root found:

• noop
• change to file's directory
• change to home directory

Root found:

• change directory (:cd)
• change local directory (:lcd)
• echo new directory or not

Miscellaneous

If bar is a symlinked directory:

• expand('/foo/bar/', ':p') resolves the symlink
• expand('/foo/bar', ':p') does not resolve the symlink