Collapse unique nested paths in dired with dired-collapse-mode

Often times we find ourselves in a situation where a single file or directory is nested in a chain of nested directories with no other content. This is sometimes due to various mandatory layouts demanded by packaging tools or tools generating these deeply-nested "unique" paths to disambiguate architectures or versions (but we often use only one anyway). If the user wants to access these directories they have to quite needlessly drill-down through varying number of "uninteresting" directories to get to the content.

This minor mode is in main inspired by how GitHub renders these paths: if there is a chain of directories where each one only has one child, they are concatenated together and shown on the first level in this collapsed form. When the user clicks this collapsed directory they are immediately brought to the deepest directory with some actual content.

In case the deepest directory contains only a single file dired-collapse-mode differs a bit in that this file is displayed instead of the last directory. This way we can get directly to the file itself. This is often helpful with config files which are stored in their own directories, for example in ~/.config/foo/config and similar situations.

The files or directories re-inserted in this manner will also have updated permissions, file sizes and modification dates so they truly correspond to the properties of the file being shown.

The path to the deepest file is dimmed with the shadow face so that it does not distract but at the same time is still available for inspection.

The mode is integrated with dired-rainbow so the nested files are properly colored according to user's rules.

After collapsing:

This package was created mainly due to the excellent feature request by the GitHub user @kidd. Thanks!