De-duplicate results from find references

We might have duplicate results for multiple references inside a macro. In this case we only want to show the macro attribute or macro expansion expr/decl once.

Fixes #1047
rdar://122237704

Author: ahoppen

Sources/SourceKitLSP/SourceKitServer.swift

@@ -2000,7 +2000,7 @@ extension SourceKitServer {
       }
       return index.occurrences(ofUSR: usr, roles: roles).compactMap { indexToLSPLocation($0.location) }
     }
-    return locations.sorted()
+    return locations.unique.sorted()
   }
 
   private func indexToLSPCallHierarchyItem(

Tests/SourceKitLSPTests/ReferencesTests.swift

@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import LanguageServerProtocol
+import SKTestSupport
+import XCTest
+
+/// Tests that test the overall state of the SourceKit-LSP server, that's not really specific to any language
+final class ReferencesTests: XCTestCase {
+  func testReferencesInMacro() async throws {
+    let ws = try await IndexedSingleSwiftFileWorkspace(
+      """
+      import Observation
+
+      @available(macOS 14.0, *)
+      1️⃣@Observable
+      class 2️⃣Foo {
+        var x: Int = 2
+      }
+      """
+    )
+
+    let response = try await ws.testClient.send(
+      ReferencesRequest(
+        textDocument: TextDocumentIdentifier(ws.fileURI),
+        position: ws.positions["2️⃣"],
+        context: ReferencesContext(includeDeclaration: true)
+      )
+    )
+    XCTAssertEqual(
+      response,
+      [
+        Location(uri: ws.fileURI, range: Range(ws.positions["1️⃣"])),
+        Location(uri: ws.fileURI, range: Range(ws.positions["2️⃣"])),
+      ]
+    )
+  }
+}