[[!comment format=mdwn
 username="joey"
 subject="""comment 1"""
 date="2017-02-20T15:53:29Z"
 content="""
It is indeed to support things like `.tar.gz`, `.pdf.gz` etc.

There's really no way to distinguish between what's desired to be part of
the extension and not, other than heuristics. The heuristics for this are
fairly narrow. Other than not allowing purely numeric parts in extenssions,
or only taking the last extension, I don't see any change that could help
with this case.

Bear in mind that the only reason the extension is included at all is
because some strange programs, especially on OSX, follow symlinks and look
at the symlink of the link destination to try to guess what kind of file it
is. There's no good reason for a program to do that, and if you're not
using programs with that problem, you can just use the SHA256 backend and
leave off the extensions.

Bearing in mind that the extension is part of a big long ugly key name that
you don't generally need to do anything with, including an extra short
possibly not-really-extension part doesn't seem like a usability problem.
The only real problem would be if you had two files with the same content,
but different "extensions", since this would prevent them being
deduplicated to the same key.
"""]]