Add support for fish-lsp

[cswimr]

This PR adds support for fish-lsp.

Binary resolution works how you would expect; we first check lsp.fish-lsp.binary.path for a set binary path, then we check $PATH for a fish-lsp binary, and finally we install fish-lsp from NPM if another binary can't be found. Note that this has a runtime requirement on the fish shell being present in $PATH, or the LSP setup will fail. I decided to make this error in the extension instead of letting the LSP error, so that users get a clearer error message.

I didn't include any LSP settings, nor did I test any initialization options. Initialization options should work, I think? Didn't feel like adding support for LSP settings, it could be done in the future through environment variables though if I understand fish-lsp's help output correctly.

This is my first time really using Rust. I did test this, and everything works fine as far as I can tell, but I'm not sure on general code quality / best practices and such.

LLM Usage: LLMs were used to assist with figuring out some Rust related stuff, but did not write any code. This is all human-written slopcode, not LLM-generated slopcode.
Edit: Technically used some coderabbit-suggested code, after review. Even this was tweaked a little though.

Closes #8.

Summary by CodeRabbit

Summary by CodeRabbit

• New Features

  • Added a Fish language server extension for the Zed editor, enabling Fish development support with configurable server arguments and environment settings, plus automatic resolution/installation of the Fish LSP server.

• Chores

  • Updated extension metadata to version 0.2.0 and registered the “Fish LSP” language server for Fish.
  • Added Rust crate configuration for the extension and pinned the Rust toolchain to the stable channel.
  • Updated ignore rules to skip the /target directory.

[coderabbitai]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 38cc592f-faeb-4c5d-8ab8-29ca9a2100da

📥 Commits

Reviewing files that changed from the base of the PR and between b113453 and 03d08de.

📒 Files selected for processing (1)

• src/lib.rs

📝 Walkthrough

Walkthrough

This PR adds the zed-fish extension crate, configures the extension manifest, and implements fish-lsp resolution, install/update handling, and command construction.

Changes

fish-lsp Zed Extension

Layer / File(s)	Summary
Project scaffolding and extension manifest Cargo.toml, rust-toolchain.toml, .gitignore, extension.toml	Defines the zed-fish crate, pins Rust to stable, ignores /target, updates the extension version, and adds the fish-lsp language server entry for Fish.
Settings and NPM support src/lib.rs	Defines constants and helpers for settings, arguments, environment construction, and NPM install/update status handling.
Binary resolution and command wiring src/lib.rs	Requires fish, resolves fish-lsp from configured path, PATH, or NPM, and builds the extension command with the resolved binary and environment.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Poem

🐇 I hop through the burrow where fish-lsp sings,
With stable Rust boots and a few tidy things.
From PATH to NPM, the server finds home,
Then start gets the whiskers and off it can roam.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding fish-lsp support.
Linked Issues check	✅ Passed	The PR adds fish-lsp support for the Fish extension, matching issue #8's request.
Out of Scope Changes check	✅ Passed	The modified files are all directly related to adding fish-lsp support and packaging it.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/lib.rs`:
- Around line 67-85: The current code uses the `?` operator on the version
checking calls (npm_package_installed_version and npm_package_latest_version)
and the install method call (Fish::install_npm_language_server), which
propagates errors and blocks LSP startup. Instead, wrap the version checking and
update operations in error handling logic that gracefully handles failures. When
npm_package_installed_version, npm_package_latest_version, or the
Fish::install_npm_language_server call fails, check if a local binary already
exists at the expected path. If a local binary exists, allow the LSP to proceed
despite the version check or update failure. Only propagate an error if no local
binary is available. This way, transient network or registry issues do not block
LSP startup when a usable binary is already present.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: ef4e7f93-a2e9-4808-b924-b283061f0da9

📥 Commits

Reviewing files that changed from the base of the PR and between d225d1c and 6598fdc.

⛔ Files ignored due to path filters (1)

• Cargo.lock is excluded by !**/*.lock

📒 Files selected for processing (5)

• .gitignore
• Cargo.toml
• extension.toml
• rust-toolchain.toml
• src/lib.rs

[hasit]

@cswimr thank you for the PR. I will review it by the end of the week.

[cswimr]

Addressed review feedback. I also made a couple other changes, primarily stylistic ones (like using Self instead of Fish). Tweaked a few error messages as well.