Use more LSP data when falling back to regular completions label (#23909)

Closes https://github.com/zed-industries/zed/issues/23590
Closes https://x.com/steeve/status/1865129235536568555

Before:

<img width="773" alt="before"
src="https://github.com/user-attachments/assets/129a8d12-9298-4bf5-8f2d-b3292c2562bf"
/>


After:

<img width="768" alt="after"
src="https://github.com/user-attachments/assets/e0516fb3-b02a-48be-8923-63bba05fdb69"
/>


The list obviously needs some solution for the cut-off part of the
completion label, but this is the reality for all extensions'
completions too, so one step at a time.


Release Notes:

- Improved default completion label fallback

crates/editor/src/editor_tests.rs

@@ -11282,7 +11282,7 @@ async fn test_completions_resolve_updates_labels_if_filter_text_matches(
     cx.simulate_keystroke(".");
 
     let item1 = lsp::CompletionItem {
-        label: "id".to_string(),
+        label: "method id()".to_string(),
         filter_text: Some("id".to_string()),
         detail: None,
         documentation: None,
@@ -11332,7 +11332,7 @@ async fn test_completions_resolve_updates_labels_if_filter_text_matches(
                         .iter()
                         .map(|completion| &completion.label.text)
                         .collect::<Vec<_>>(),
-                    vec!["id", "other"]
+                    vec!["method id()", "other"]
                 )
             }
             CodeContextMenu::CodeActions(_) => panic!("Should show the completions menu"),
@@ -11387,7 +11387,7 @@ async fn test_completions_resolve_updates_labels_if_filter_text_matches(
                         .iter()
                         .map(|completion| &completion.label.text)
                         .collect::<Vec<_>>(),
-                    vec!["method id()", "other"],
+                    vec!["method id() Now resolved!", "other"],
                     "Should update first completion label, but not second as the filter text did not match."
                 );
             }

crates/language/src/language.rs

@@ -1750,6 +1750,58 @@ impl Grammar {
 }
 
 impl CodeLabel {
+    pub fn fallback_for_completion(
+        item: &lsp::CompletionItem,
+        language: Option<&Language>,
+    ) -> Self {
+        let highlight_id = item.kind.and_then(|kind| {
+            let grammar = language?.grammar()?;
+            use lsp::CompletionItemKind as Kind;
+            match kind {
+                Kind::CLASS => grammar.highlight_id_for_name("type"),
+                Kind::CONSTANT => grammar.highlight_id_for_name("constant"),
+                Kind::CONSTRUCTOR => grammar.highlight_id_for_name("constructor"),
+                Kind::ENUM => grammar
+                    .highlight_id_for_name("enum")
+                    .or_else(|| grammar.highlight_id_for_name("type")),
+                Kind::FIELD => grammar.highlight_id_for_name("property"),
+                Kind::FUNCTION => grammar.highlight_id_for_name("function"),
+                Kind::INTERFACE => grammar.highlight_id_for_name("type"),
+                Kind::METHOD => grammar
+                    .highlight_id_for_name("function.method")
+                    .or_else(|| grammar.highlight_id_for_name("function")),
+                Kind::OPERATOR => grammar.highlight_id_for_name("operator"),
+                Kind::PROPERTY => grammar.highlight_id_for_name("property"),
+                Kind::STRUCT => grammar.highlight_id_for_name("type"),
+                Kind::VARIABLE => grammar.highlight_id_for_name("variable"),
+                Kind::KEYWORD => grammar.highlight_id_for_name("keyword"),
+                _ => None,
+            }
+        });
+
+        let label = &item.label;
+        let label_length = label.len();
+        let runs = highlight_id
+            .map(|highlight_id| vec![(0..label_length, highlight_id)])
+            .unwrap_or_default();
+        let text = if let Some(detail) = &item.detail {
+            format!("{label} {detail}")
+        } else if let Some(description) = item
+            .label_details
+            .as_ref()
+            .and_then(|label_details| label_details.description.as_ref())
+        {
+            format!("{label} {description}")
+        } else {
+            label.clone()
+        };
+        Self {
+            text,
+            runs,
+            filter_range: 0..label_length,
+        }
+    }
+
     pub fn plain(text: String, filter_text: Option<&str>) -> Self {
         let mut result = Self {
             runs: Vec::new(),

crates/project/src/lsp_store.rs

@@ -4380,7 +4380,8 @@ impl LspStore {
 
         // NB: Zed does not have `details` inside the completion resolve capabilities, but certain language servers violate the spec and do not return `details` immediately, e.g. https://github.com/yioneko/vtsls/issues/213
         // So we have to update the label here anyway...
-        let mut new_label = match snapshot.language() {
+        let language = snapshot.language();
+        let mut new_label = match language {
             Some(language) => {
                 adapter
                     .labels_for_completions(&[completion_item.clone()], language)
@@ -4391,9 +4392,9 @@ impl LspStore {
         .pop()
         .flatten()
         .unwrap_or_else(|| {
-            CodeLabel::plain(
+            CodeLabel::fallback_for_completion(
-                completion_item.label,
+                &completion_item,
-                completion_item.filter_text.as_deref(),
+                language.map(|language| language.as_ref()),
             )
         });
         ensure_uniform_list_compatible_label(&mut new_label);
@@ -8079,10 +8080,7 @@ async fn populate_labels_for_completions(
         };
 
         let mut label = label.unwrap_or_else(|| {
-            CodeLabel::plain(
+            CodeLabel::fallback_for_completion(&lsp_completion, language.as_deref())
-                lsp_completion.label.clone(),
-                lsp_completion.filter_text.as_deref(),
-            )
         });
         ensure_uniform_list_compatible_label(&mut label);
 
@@ -8883,7 +8881,7 @@ fn include_text(server: &lsp::LanguageServer) -> Option<bool> {
 /// Completion items are displayed in a `UniformList`.
 /// Usually, those items are single-line strings, but in LSP responses,
 /// completion items `label`, `detail` and `label_details.description` may contain newlines or long spaces.
-/// Many language plugins construct these items by joining these parts together, and we may fall back to `CodeLabel::plain` that uses `label`.
+/// Many language plugins construct these items by joining these parts together, and we may use `CodeLabel::fallback_for_completion` that uses `label` at least.
 /// All that may lead to a newline being inserted into resulting `CodeLabel.text`, which will force `UniformList` to bloat each entry to occupy more space,
 /// breaking the completions menu presentation.
 ///