You can now apply overlays to the grammar derivations via
`grammarOverlays`. Also, the `src` in the derivation is now properly
unpacked to the build directory, allowing the user to mutate the source
files if they want to.
Here we perform a shallow fetch using builtins.fetchTree. In order
to make this work, we need to specify the `ref' for any repository
that doesn't have `master' as its default branch (I'm not sure why
this limitation exists since we don't need this when performing
the shallow fetch in `--grammar build')
This `ref' field is ignored by helix, so I have left it undocumented
for now, but I could be open to documenting it.
This commit replaces the out-of-date builder in the flake which relied
on submodules for fetching and the compiler for building. Now we
disable fetching and building explicitly with the environment variable
and then use builtins.fetchGit and a derivation mostly derived from
upstream to compile the grammars.
Anecdotally, this is still quite slow as builtins.fetchGit does not
seem to do shallow clones. I'm not sure I see a way around it though
without recording sha256s, which seems cumbersome.
