ghci recompilation avoidance

[Evan Laforge]

On Tue, May 29, 2018 at 11:46 PM, Kim-Ee Yeoh <ky3 at atamo.com> wrote:
>> It turns out that git checkouts update the modtime on checked-out files,
>> even
> when they get reverted back to their original contents.
>
> Looks to me the problem's right here. Namely, git checkout.
>
> If the contents didn't change, the modtime shouldn't either. What's the
> reason behind changing it?

The contents do change, but then they change back again.  Say you
visit another branch then come back.

> Have you brought this up to the git maintainers? Compensating for flaws in
> co-tools costs code and complexity in ghc we would rather do without.

Here's an explanation with some links:

https://confluence.atlassian.com/bbkb/preserving-file-timestamps-with-git-and-mercurial-781386524.html

> In the meantime, it shouldn't be hard to kludge up some shell scripts that
> run before and after git checkout to reset the modtime back to what it
> should be.

That sounds like code and complexity too!  Only it would be repeated
in every repo.  And it sounds pretty hard too.  I'd have to keep and
update a Map (Branch, FilePath) ModTime, and hook every checkout to
record and restore every modified file.  At that point I've more or
less written my own checkout command.