Extract Haskell support into an extension (#9814)

This PR extracts Haskell support into an extension and removes the
built-in Haskell support from Zed.

I tested out the extension locally in a Nix shell using `nix-shell -p
ghc haskell-language-server` to confirm the language server still
operated as expected:

<img width="341" alt="Screenshot 2024-03-26 at 11 26 26 AM"
src="https://github.com/zed-industries/zed/assets/1486634/df16fd38-4046-4a45-ac9f-c2b85bffe5c0">

Release Notes:

- Removed built-in support for Haskell, in favor of making it available
as an extension. The Haskell extension will be suggested for download
when you open a `.hs` file.

extensions/haskell/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "zed_haskell"
+version = "0.0.1"
+edition = "2021"
+publish = false
+license = "Apache-2.0"
+
+[lints]
+workspace = true
+
+[lib]
+path = "src/haskell.rs"
+crate-type = ["cdylib"]
+
+[dependencies]
+zed_extension_api = "0.0.4"

extensions/haskell/LICENSE-APACHE

@@ -0,0 +1 @@
+../../LICENSE-APACHE

extensions/haskell/extension.toml

@@ -0,0 +1,19 @@
+id = "haskell"
+name = "Haskell"
+description = "Haskell support for Zed"
+version = "0.0.1"
+schema_version = 1
+authors = [
+    "Marshall Bowers <elliott.codes@gmail.com>",
+    "Pseudomata <pseudomata@proton.me>",
+    "Lei <45155667+leifu1128@users.noreply.github.com>"
+]
+repository = "https://github.com/zed-industries/zed"
+
+[language_servers.hls]
+name = "Haskell Language Server"
+language = "Haskell"
+
+[grammars.haskell]
+repository = "https://github.com/tree-sitter/tree-sitter-haskell"
+commit = "8a99848fc734f9c4ea523b3f2a07df133cbbcec2"

extensions/haskell/languages/haskell/brackets.scm

@@ -0,0 +1,3 @@
+("(" @open ")" @close)
+("[" @open "]" @close)
+("{" @open "}" @close)

extensions/haskell/languages/haskell/config.toml

@@ -0,0 +1,14 @@
+name = "Haskell"
+grammar = "haskell"
+path_suffixes = ["hs"]
+autoclose_before = ",=)}]"
+line_comments = ["-- "]
+block_comment = ["{- ", " -}"]
+brackets = [
+    { start = "{", end = "}", close = true, newline = true },
+    { start = "[", end = "]", close = true, newline = true },
+    { start = "(", end = ")", close = true, newline = true },
+    { start = "\"", end = "\"", close = true, newline = false },
+    { start = "'", end = "'", close = true, newline = false },
+    { start = "`", end = "`", close = true, newline = false },
+]

extensions/haskell/languages/haskell/highlights.scm

@@ -0,0 +1,156 @@
+;; Copyright 2022 nvim-treesitter
+;;
+;; Licensed under the Apache License, Version 2.0 (the "License");
+;; you may not use this file except in compliance with the License.
+;; You may obtain a copy of the License at
+;;
+;;     http://www.apache.org/licenses/LICENSE-2.0
+;;
+;; Unless required by applicable law or agreed to in writing, software
+;; distributed under the License is distributed on an "AS IS" BASIS,
+;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+;; See the License for the specific language governing permissions and
+;; limitations under the License.
+
+;; ----------------------------------------------------------------------------
+;; Literals and comments
+
+(integer) @number
+(exp_negation) @number
+(exp_literal (float)) @float
+(char) @character
+(string) @string
+
+(con_unit) @symbol  ; unit, as in ()
+
+(comment) @comment
+
+
+;; ----------------------------------------------------------------------------
+;; Punctuation
+
+[
+  "("
+  ")"
+  "{"
+  "}"
+  "["
+  "]"
+] @punctuation.bracket
+
+[
+  (comma)
+  ";"
+] @punctuation.delimiter
+
+
+;; ----------------------------------------------------------------------------
+;; Keywords, operators, includes
+
+[
+  "forall"
+  "∀"
+] @keyword
+
+(pragma) @constant
+
+[
+  "if"
+  "then"
+  "else"
+  "case"
+  "of"
+] @keyword
+
+(exp_lambda_cases "\\" ("cases" @variant))
+
+[
+  "import"
+  "qualified"
+  "module"
+] @keyword
+
+[
+  (operator)
+  (constructor_operator)
+  (type_operator)
+  (tycon_arrow)
+  (qualified_module)  ; grabs the `.` (dot), ex: import System.IO
+  (all_names)
+  (wildcard)
+  "="
+  "|"
+  "::"
+  "=>"
+  "->"
+  "<-"
+  "\\"
+  "`"
+  "@"
+] @operator
+
+(module) @title
+
+[
+  (where)
+  "let"
+  "in"
+  "class"
+  "instance"
+  "data"
+  "newtype"
+  "family"
+  "type"
+  "as"
+  "hiding"
+  "deriving"
+  "via"
+  "stock"
+  "anyclass"
+  "do"
+  "mdo"
+  "rec"
+  "infix"
+  "infixl"
+  "infixr"
+] @keyword
+
+
+;; ----------------------------------------------------------------------------
+;; Functions and variables
+
+(variable) @variable
+(pat_wildcard) @variable
+
+(signature name: (variable) @type)
+(function
+  name: (variable) @function
+  patterns: (patterns))
+((signature (fun)) . (function (variable) @function))
+((signature (context (fun))) . (function (variable) @function))
+((signature (forall (context (fun)))) . (function (variable) @function))
+
+(exp_infix (variable) @operator)  ; consider infix functions as operators
+
+(exp_infix (exp_name) @function (#set! "priority" 101))
+(exp_apply . (exp_name (variable) @function))
+(exp_apply . (exp_name (qualified_variable (variable) @function)))
+
+
+;; ----------------------------------------------------------------------------
+;; Types
+
+(type) @type
+(type_variable) @type
+
+(constructor) @constructor
+
+; True or False
+((constructor) @_bool (#match? @_bool "(True|False)")) @boolean
+
+
+;; ----------------------------------------------------------------------------
+;; Quasi-quotes
+
+(quoter) @function
+; Highlighting of quasiquote_body is handled by injections.scm

extensions/haskell/languages/haskell/indents.scm

@@ -0,0 +1,3 @@
+(_ "[" "]" @end) @indent
+(_ "{" "}" @end) @indent
+(_ "(" ")" @end) @indent

extensions/haskell/languages/haskell/outline.scm

@@ -0,0 +1,26 @@
+(adt
+  "data" @context
+  name: (type) @name) @item
+
+(type_alias
+  "type" @context
+  name: (type) @name) @item
+
+(newtype
+  "newtype" @context
+  name: (type) @name) @item
+
+(signature
+  name: (variable) @name) @item
+
+(class
+  "class" @context
+  (class_head) @name) @item
+
+(instance
+  "instance" @context
+  (instance_head) @name) @item
+
+(foreign_import
+  "foreign" @context
+  (impent) @name) @item

extensions/haskell/src/haskell.rs

@@ -0,0 +1,27 @@
+use zed_extension_api::{self as zed, Result};
+
+struct HaskellExtension;
+
+impl zed::Extension for HaskellExtension {
+    fn new() -> Self {
+        Self
+    }
+
+    fn language_server_command(
+        &mut self,
+        _config: zed::LanguageServerConfig,
+        worktree: &zed::Worktree,
+    ) -> Result<zed::Command> {
+        let path = worktree
+            .which("haskell-language-server-wrapper")
+            .ok_or_else(|| "hls must be installed via ghcup".to_string())?;
+
+        Ok(zed::Command {
+            command: path,
+            args: vec!["lsp".to_string()],
+            env: Default::default(),
+        })
+    }
+}
+
+zed::register_extension!(HaskellExtension);