fix(editor): List identical completion items once

kotlin-language-server repeats a class once per classpath entry declaring
it, so `String()` and `String` were listed three times each.

src/editor/lsp/completion.test.ts

@@ -4,7 +4,14 @@ import { EditorView } from "@codemirror/view";
 import type { CompletionItem } from "@/bindings";
 import type { EditorDocContext } from "@/editor/api";
 import { lspDoc } from "./lsp";
-import { completionSymbolKind, identifierEnd, toCmCompletion, triggerCharacter, typeColumnText } from "./completionItems";
+import {
+  completionSymbolKind,
+  identifierEnd,
+  toCmCompletion,
+  triggerCharacter,
+  typeColumnText,
+  withoutDuplicates,
+} from "./completionItems";
 import {
   applyLspCompletion,
   callParens,
@@ -75,6 +82,13 @@ describe("toCmCompletion", () => {
     expect(toCmCompletion(item({ label: "foo", filterText: "foo_bar" })).label).toBe("foo_bar");
   });
 
+  it("lists identical items once", () => {
+    const ctor = item({ label: "String()", kind: "constructor", data: "1" });
+    const overload = item({ label: "String()", kind: "constructor", labelDetail: "(bytes: ByteArray)" });
+    const out = withoutDuplicates([ctor, { ...ctor, data: "2" }, overload, { ...ctor, server: 2 }]);
+    expect(out).toEqual([ctor, overload, { ...ctor, server: 2 }]);
+  });
+
   it("boosts preselected and demotes deprecated items", () => {
     expect(toCmCompletion(item({ preselect: true })).boost).toBe(99);
     expect(toCmCompletion(item({ deprecated: true })).boost).toBeLessThan(0);

src/editor/lsp/completion.ts

@@ -35,7 +35,14 @@ import {
   type RequestId,
 } from "@/platform/ipc";
 import { useProject } from "@/platform/project";
-import { completionSymbolKind, identifierEnd, toCmCompletion, triggerCharacter, typeColumnText } from "./completionItems";
+import {
+  completionSymbolKind,
+  identifierEnd,
+  toCmCompletion,
+  triggerCharacter,
+  typeColumnText,
+  withoutDuplicates,
+} from "./completionItems";
 import { lspSnippetToCm, snippetVariables } from "./snippet";
 import { docOf, isUnavailable, lspDoc, lspRequest, reportLspError } from "./lsp";
 import { offsetToPos, posToOffset, textEditsToChanges } from "./positions";
@@ -437,9 +444,11 @@ async function lspCompletionSource(ctx: CompletionContext): Promise<CompletionRe
   const req: RequestContext = { doc: doc.doc, path: doc.path, language: doc.uiMode, pos: ctx.pos, text: ctx.state.doc };
   const prefs = editorPrefs().completion;
   const typed = word?.text ?? "";
-  let items = prefs.matchCase
-    ? list.items.filter((it) => matchesCase(it.filterText ?? it.label, typed, prefs.caseSensitivity))
-    : list.items;
+  let items = withoutDuplicates(
+    prefs.matchCase
+      ? list.items.filter((it) => matchesCase(it.filterText ?? it.label, typed, prefs.caseSensitivity))
+      : list.items,
+  );
   // A server snippet named like a live template (jdtls `sout`, `fori`) would be listed twice; the template wins.
   if (items.some((it) => it.kind === "snippet")) {
     const own = await contributedSource(ctx);

src/editor/lsp/completionItems.ts

@@ -65,6 +65,22 @@ function extendsLabel(item: CompletionItem): boolean {
   return item.filterText!.startsWith(item.label) && /^[^\p{L}\p{N}_$]/u.test(rest);
 }
 
+/**
+ * Items that look and insert the same, listed once. kotlin-language-server
+ * repeats a class once per classpath entry declaring it (`String()` ×3);
+ * these all have their own `apply` (see `makeCompletion`), so CodeMirror
+ * wouldn't merge them.
+ */
+export function withoutDuplicates(items: readonly CompletionItem[]): CompletionItem[] {
+  const seen = new Set<string>();
+  return items.filter((it) => {
+    const key = JSON.stringify([it.server, it.label, it.labelDetail, it.detail, it.kind, it.insertText, it.additionalEdits]);
+    if (seen.has(key)) return false;
+    seen.add(key);
+    return true;
+  });
+}
+
 const IMPORT_SOURCE = [
   /^\s*from\s+([\w.]+)\s+import\b/m, // Python
   /^\s*import\s+(?:static\s+)?([\w.]+?)\.\w+;?\s*$/m, // Java, Kotlin