Traverse symlinks when resolving migrations

[tgeoghegan]

When enumerating the source directory seeking migration files, sqlx ignores entries that aren't files. This was previously reported as #614 and fixed in #985 but apparently regressed somewhere along the way. This commit reintroduces the fix from #985 to the current implementation: use std::fs::metadata instead of std::fs::DirEntry::metadata. The former is documented to traverse symlinks; the latter does not.

[tgeoghegan]

I would love to add a test to stop this from regressing, but it's not obvious where to do so. It looks like there are tests for migrations in tests/migrate and tests/postgres/migrate.rs, but AFAICT neither gets run when I invoke tests/x.py as instructed by tests/README.md.

[abonander]

@tgeoghegan tests/x.py is old and not very well maintained. I personally don't use it, and neither does the Github Actions workflow.

tests/migrate asserts that Migrator::new() and migrate!() behave the same, so I reckon that's the best place to put the regression test.

[abonander]

@tgeoghegan do you have time to write a regression test so I can get this merged? If not, can you tell me if you're mainly symlinking the migrations/ directory itself or the individual files within? With that I can add the regression test myself.

[tgeoghegan]

@abonander Thank you for the pointers, and apologies for the late reply (I was on vacation). I added a test that I think should do the trick; let's see how it goes in CI.

[tgeoghegan]

🎉 Thank you for reviewing and taking the change!