Re: [PATCH 2/2] submodule: munge paths to submodule git directories

From: Stefan Beller <sbeller@google.com>
Date: Aug 29, 2018, 18:10 UTC
Message-ID: <CAGZ79kZv4BjRq=kq_1UeT2Kn38OZwYFgnMsTe6X_WP41=hBtSQ@mail.gmail.com>
In-Reply-To: <20180829052519.GA17253@sigill.intra.peff.net>

On Tue, Aug 28, 2018 at 10:25 PM Jeff King <peff@peff.net> wrote:

Show 30 quoted lines

>
> On Tue, Aug 28, 2018 at 02:35:25PM -0700, Stefan Beller wrote:
>
> > 3) (optional) instead of putting it all in modules/, use another
> >    directory gitmodules/ for example. this will make sure we can tell
> >    if a repository has been converted or is stuck with a setup of a
> >    current git.
>
> I actually kind of like that idea, as it makes the interaction between
> old and new names much simpler to reason about.
>
> And since old code won't know about the new names anyway, there's in
> theory no downside. In practice, of course, the encoding may often be a
> noop, and lazy scripts would continue to work most of the time if you
> didn't change out the prefix directory. I'm not sure if that is an
> argument for the scheme (because it will suss out broken scripts more
> consistently) or against it (because 99% of the time those old scripts
> would just happen to work).
>
> > > This is exactly the reason why I wanted to get some opinions on what the
> > > best thing to do here would be.  I _think_ the best thing would probably
> > > be to write a specific routine to do the conversion, and it wouldn't
> > > even have to be all that complex.  Basically I'm just interested in
> > > converting '/' characters so that things no longer behave like
> > > nested directories.
> >
> > Yeah, then let's just convert '/' with as little overhead as possible.
>
> Do you care about case-folding issues (e.g., submodules "FOO" and "foo"
> colliding)?

I do. :(

2d84f13dcb6 (config: fix case sensitive subsection names on writing, 2018-08-08) explains the latest episode of case folding with submodules involved.

> I'm OK if the answer is "no", but if you do want to deal with it, the
> time is probably now.

Good point. But as soon as we start discussing case sensitivity, we are drawn down the rabbit hole of funny file names. (Try naming a submodule "CON1" and obtain it on Windows for example) So we would need to have a file system specific encoding function for submodule names, which sounds like a maintenance night mare.

The CON1 example shows that URL encoding may not be enough on Windows and we'd have to extend the encoding if we care about FS issues.

Another example would be "a" and "a\b" which would be a mess in Windows as the '\' would work as a dir separator whereas these two names were ok on linux. This would be fixed with url encoding.

URL encoding would not fix the case-folding issue that you mentioned above.

So if I was thinking in the scheme presented above, we could just have another rule that is

  [A-Z]  -> _[a-z]

(lowercase capital letters and escape them with an underscore)

But with that rule added, we are inventing a really complicated encoding scheme already.