Updated error message to indicate that modules must start with a letter

[hughesjs]

This partially addresses #8252 by ensuring that the produced error message indicates that a module name must start with a letter.

[Leonidas-from-XIV]

Looks like a reasonable improvement. Reminds me of e.g. 0install, which could run into this issue.

[Leonidas-from-XIV]

@hughesjs Can you promote the test case failures?

[hughesjs]

@Leonidas-from-XIV - Will give it a shot later this evening. No promises though, I've spent all of 2 hours writing ocaml and half of that was working out why I couldn't build the base project, I'll let you know how I get on

[Leonidas-from-XIV]

If you do dune runtest it will run the tests locally (and trigger the failures you see on CI) and you can call dune promote <path-of-test> to automatically promote the ones where the message changed to have the new message and commit those.

[Alizter]

You don't even have to run the entire test suite. Just do the following:

$ ./dune.exe build @github5273 @github7600 @pp @fmt
$ ./dune.exe promote

That just runs the tests that failed in CI and code formatting.
(also run make bootstrap if you haven't already done that).

[hughesjs]

Huh, didn't know that was a thing. Cheers! Will do it when I'm back at my own machine

[hughesjs]

Right, that's the test cases promoted

[Leonidas-from-XIV]

I think it is ready to be merged.

[Leonidas-from-XIV]

I've rebased the change upon our current main branch due to an annoying formatting change that sucks to resolve manually.

[Alizter]

@rgrinberg Can you take a look?

[hughesjs]

Thanks for merging this guys, sorry I've not been particularly active here, life's being a bit hectic