Better support for non-primary LSP extensions

[notpeter]

Context:

• Add default settings for LaTeX #27286

Currently when there are multiple language servers available for a given language, there is no way for an Extension to specify which language server should be the primary language server (first in the language_servers array) for a given language.

Proposal: Add an additional key to extensions.toml to optional designate their Extension provided LSPs as non-primary (E.g. primary = false; with a default of true)

[language_servers.cpsell]
name = "cspell"
primary = false
languages = [
  "AsciiDoc",
  "Astro",
  "Bash",

Which will make it so that the default "language_servers": ["..."] for the "LaTeX" language, if a user had the Latex, Cspell and Typos extensions (assuming the last two have primary = false) would expand to ["texlab", "cspell", "typos"] which is I believe the behavior users would want. There have been similar uses with users of the ruff LSP which only provides linting/formatting but not Goto Definition, etc.

Reasoning: Currently this requires shipping Zed global default.json entries so that these extensions function properly out of the box.

zed/assets/settings/default.json

Lines 1171 to 1172 in e273de5

	"Astro": {
	"language_servers": ["astro-language-server", "..."],

zed/assets/settings/default.json

Lines 1210 to 1215 in e273de5

	"Elixir": {
	"language_servers": ["elixir-ls", "!next-ls", "!lexical", "..."]
	},
	"Erlang": {
	"language_servers": ["erlang-ls", "!elp", "..."]
	},

zed/assets/settings/default.json

Lines 1229 to 1231 in e273de5

	"HEEX": {
	"language_servers": ["elixir-ls", "!next-ls", "!lexical", "..."]
	},

zed/assets/settings/default.json

Lines 1279 to 1281 in e273de5

	"Ruby": {
	"language_servers": ["solargraph", "!ruby-lsp", "!rubocop", "..."]
	},

Discussion:

There has been previous discussion about potential conflicts between two extensions, for example the R extension provides a tree-sitter with syntax highlighting for R and support for the languageserver R LSP; but there are other folks who want to provide the alternate air LSP which may require cooperation between extensions to be fully supported.

• "Native" language support for R? #25758 (comment)

Alternate implementations:

1. Add a key to ${LANGUAGE}/config.toml which supports providing a default value for the language_servers key for that language.
2. Add an API to zed_extensions which supports extensions providing this information dynamically (not sure the best design)

Edit: Perhaps this will all be negated depending on how this is handled:

• Multiple language servers on one language #24100

[notpeter]

I found some additional context:

• Providing primary/secondary language servers in an extension #15279
• extensions: Allow defining language servers as secondary #15597

And think this should potentially addressed as part of:

• Multiple language servers on one language #24100

Or other improvements which remove the primary/secondary LSP concept entirely in zed.