Ability to specify file type prefixes for language detection

[klardotsh]

A pattern I've seen or implemented in many repos is to have Containerfile alongside a Containerfile.base - the former bundles up the app code (which changes frequently), the latter installs "system level dependencies" which generally changes far less frequently (this would be where, say, libfoo-devel gets installed for foo-gem to build against).

My Neovim config appears to auto-detect Containerfile.base as a Dockerfile (not sure if that's by way of file name or by way of the FROM blah line at the top), but I can't so far figure out how to emulate this in Helix, and further, Vim modelines don't flip Helix into Dockerfile mode, so I can't even hint at "hey, here's what you should use to highlight this!".

I'd propose something like the following, though it's probably imperfect and open to all sorts of discussion:

file-types = ["Dockerfile", "dockerfile", "Containerfile", "containerfile", { prefix = "Containerfile." }]

or maybe Containerfile.*?

[the-mikedavis]

This would also be useful for Bazel which can have filenames like BUILD.dep1, BUILD.dep2. We already support path suffixes so I think prefixes or file stems could make sense to add as well https://docs.helix-editor.com/master/languages.html#file-type-detection-and-the-file-types-key

[klardotsh]

This is gonna be one of those "famous last words" things, but: I wonder if regex matching is a useful addition to the file-types matcher. I currently can't think of anything it would add that prefix = "foo" can't do, but (1) it's a more generalized solution for any weird filetypes that come up later, and (2) maybe someone has run into cases where it would be useful already, I dunno.

I agree though that prefix = "foo" is the simpler thing to implement for now, and almost certainly more performant.