Add tree-sitters EEx and HEEx #2093
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The new revision handles a case that I come across often: a stab
clause (i.e. '->') with an empty right hand side:
Enum.map(xs, fn x ->
end)
The old version would parse the "end" token as an error.
This is technically valid syntax but more importantly it comes up
very often when editing, and the old revision would flicker between
the keyword highlight and the warning highlight.
This will become more important with the HEEx grammar being added. Error highlighting with the Elixir grammar is a bit jumpy because in some scenarios, a bit of missing syntax can force tree-sitter to give up on error recovery and mark the entire tree as an error. This ends up looking bad when editing. We don't typically highlight error nodes so I'm inclined to leave it out of the highlights here.
EEx is an templating language for Elixir. Since the incremental parsing refactor we can used combined injections which allows us to add EEx support.
HEEx is a templating engine on top of Elixir's EEx templating language specific to HTML that is included in Phoenix.LiveView (though I think the plan is to eventually include it in base Phoenix). It's a superset of EEx with some additional features like components and slots. The injections don't work perfectly because the Elixir grammar is newline sensitive (the _terminator rule). See elixir-lang/tree-sitter-elixir#24 for more information.
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archseer
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Apr 13, 2022
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EEx and HEEx are templating languages for Elixir.
I thought about pulling in HEEx before (#881) but it needed the incremental injections refactor in order to use combined injections (#1378).
The highlights are not perfect because of the whitespace sensitivity of tree-sitter-elixir. I've removed the error highlighting in tree-sitter-elixir queries to make it less noticeable. It may take a bit to fix that so I think we're better off adding heex with "good enough" syntax highlights for now (see also elixir-lang/tree-sitter-elixir#2 (comment)). I could be persuaded to drop the commit that removes error highlighting though.
Also updates tree-sitter-elixir with a fix for a case that bugged me during editing (elixir-lang/tree-sitter-elixir#33)