Slow rebuild time for dev extensions with grammar

[boris-schwarz]

Not sure if worth an issue or a discussion, but as far as I can tell some kind of cache for compiled grammars is needed when developing a local dev extension.

When creating an extension that uses a tree-sitter repository, installing or rebuilding the extension also compiles the provided grammars in extension.toml every time. For my currently used grammar, this takes about 2 minutes every time:

[grammars.cfhtml]
repository = "https://github.com/cfmleditor/tree-sitter-cfml"
rev = "25e888b47f50979db00a25cb1fd6c857a615d5be"
path = "./cfhtml"

The function compile_grammar() in zed/crates/extension/src/extension_builder.rs always compiles all grammars in the extension manifest, I cannot find any mechanic for caching, for instance the struct GrammarManifestEntry only allows repository, rev (alias commit) and path, but no other configuration. Also the flag release in CompileExtensionOptions does not play a role.

This is most likely intentional, so no pre-compiled code can be sneaked in, however during local development mode it would make sense to be able to skip the compilation of the grammars.

I could imagine a workflow like this:
If install_dev_extension() or rebuild_dev_extension() are called, compile_extension() additionally checks if grammars/my_grammar.wasm exists, if it does the clang compilation for that grammar will be skipped. It would be then in the responsibility of the developer to delete the grammars/my_grammar/ and grammars/my_grammar.wasm, as it is currently also the case if the git commit hash is being changed.

What do you think? Did I miss something or is anybody also having long rebuild times?

Cheers, Boris