Add label_for_symbol to extension API (#10179)

This PR adds `label_for_symbol` to the extension API.

As a motivating example, we implemented `label_for_symbol` for the
Haskell extension.

Release Notes:

- N/A

Co-authored-by: Max <max@zed.dev>

extensions/haskell/Cargo.toml

@@ -13,4 +13,5 @@ path = "src/haskell.rs"
 crate-type = ["cdylib"]
 
 [dependencies]
-zed_extension_api = "0.0.4"
+# zed_extension_api = "0.0.4"
+zed_extension_api = { path = "../../crates/extension_api" }

extensions/haskell/src/haskell.rs

@@ -1,3 +1,5 @@
+use zed::lsp::{Symbol, SymbolKind};
+use zed::{CodeLabel, CodeLabelSpan};
 use zed_extension_api::{self as zed, Result};
 
 struct HaskellExtension;
@@ -9,7 +11,7 @@ impl zed::Extension for HaskellExtension {
 
     fn language_server_command(
         &mut self,
-        _config: zed::LanguageServerConfig,
+        _language_server_id: &zed::LanguageServerId,
         worktree: &zed::Worktree,
     ) -> Result<zed::Command> {
         let path = worktree
@@ -22,6 +24,44 @@ impl zed::Extension for HaskellExtension {
             env: Default::default(),
         })
     }
+
+    fn label_for_symbol(
+        &self,
+        _language_server_id: &zed::LanguageServerId,
+        symbol: Symbol,
+    ) -> Option<CodeLabel> {
+        let name = &symbol.name;
+
+        let (code, display_range, filter_range) = match symbol.kind {
+            SymbolKind::Struct => {
+                let data_decl = "data ";
+                let code = format!("{data_decl}{name} = A");
+                let display_range = 0..data_decl.len() + name.len();
+                let filter_range = data_decl.len()..display_range.end;
+                (code, display_range, filter_range)
+            }
+            SymbolKind::Constructor => {
+                let data_decl = "data A = ";
+                let code = format!("{data_decl}{name}");
+                let display_range = data_decl.len()..data_decl.len() + name.len();
+                let filter_range = 0..name.len();
+                (code, display_range, filter_range)
+            }
+            SymbolKind::Variable => {
+                let code = format!("{name} :: T");
+                let display_range = 0..name.len();
+                let filter_range = 0..name.len();
+                (code, display_range, filter_range)
+            }
+            _ => return None,
+        };
+
+        Some(CodeLabel {
+            spans: vec![CodeLabelSpan::code_range(display_range)],
+            filter_range: filter_range.into(),
+            code,
+        })
+    }
 }
 
 zed::register_extension!(HaskellExtension);