Improve highlighting of primitive type declarations

[radeksimko]

Problem Statement

This is to follow up on hashicorp/terraform-ls#827 which introduces semantic highlighting of type declarations.

Type declarations are highlighted by the server as keyword.

Our grammar currently highlights them as storage.type which seems to result in a different association in the default VSCode themes.

https://github.com/hashicorp/vscode-terraform/blob/c8b0154b8d2cc4cd67b4e68065ad6b85f8e133a8/syntaxes/terraform.tmGrammar.json#L49-L53

Grammar (only) Highlighting

Semantic Highlighting

Expected User Experience

Grammar and semantic highlighting are more aligned, i.e. type declarations are highlighted as keywords in the grammar too.

Proposal

Update terraform_type_keywords matcher?

[dbanck]

Are we sure, we want to use keyword here? Why is the server reporting this as keyword?

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Some findings:

Looking at our grammar, we're already using keyword.control for loops as default themes and the TextMate Grammar Docs docs are suggesting:

Looking at other languages (e.g. TypeScript), keyword is used for loops, too and types are reported as support.type.

We're using support.type currently for block types, e.g. variable or resource in our grammar and in the language server: https://github.com/hashicorp/terraform-ls/blob/031e30f62ab169104837fbb1e9ef2633ded73329/internal/lsp/token_encoder.go#L112-L114

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I think a more consistent way would be to use storage.type for block types, like variable and support.type for types, like string and make sure to match grammar and semantic tokens:

[radeksimko]

The main reason is that variable (token type) is already used for traversals and I couldn't think of many other good options in semantic highlighting, other than keyword, bearing in mind the syntax should provide decent out-of-the-box experience without relying on explicit mapping in extension(s).

What you're suggesting makes sense 👍🏻 but I'm not sure how well we can map that to the default semantic tokens here:
https://github.com/hashicorp/terraform-ls/blob/031e30f62ab169104837fbb1e9ef2633ded73329/internal/lsp/semtok/lsp_token_types.go#L4-L26

On that note I'd be curious to see how any language server with semantic highlighting solves this - I'm guessing they get away with e.g. type token because there aren't "block types" unlike in our DSL?