Factor related identifiers request into a separate file

This allows use to re-use related identifiers when implementing rename

Author: ahoppen

Sources/LanguageServerProtocol/Error.swift

@@ -118,6 +118,10 @@ extension ResponseError {
   public static func unknown(_ message: String) -> ResponseError {
     return ResponseError(code: .unknownErrorCode, message: message)
   }
+
+  public static func internalError(_ message: String) -> ResponseError {
+    return ResponseError(code: .internalError, message: message)
+  }
 }
 
 /// An error during message decoding.

Sources/SourceKitLSP/Swift/RelatedIdentifiers.swift

@@ -0,0 +1,68 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 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 LSPLogging
+import LanguageServerProtocol
+import SourceKitD
+
+struct RelatedIdentifier {
+  let range: Range<Position>
+}
+
+struct RelatedIdentifiersResponse {
+  let relatedIdentifiers: [RelatedIdentifier]
+}
+
+extension SwiftLanguageServer {
+  func relatedIdentifiers(at position: Position, in snapshot: DocumentSnapshot, includeNonEditableBaseNames: Bool)
+    async throws -> RelatedIdentifiersResponse
+  {
+    guard let offset = snapshot.utf8Offset(of: position) else {
+      throw ResponseError.unknown("invalid position \(position)")
+    }
+
+    let skreq = SKDRequestDictionary(sourcekitd: self.sourcekitd)
+    skreq[keys.request] = self.requests.relatedidents
+    skreq[keys.cancelOnSubsequentRequest] = 0
+    skreq[keys.offset] = offset
+    skreq[keys.sourcefile] = snapshot.uri.pseudoPath
+
+    // FIXME: SourceKit should probably cache this for us.
+    if let compileCommand = await self.buildSettings(for: snapshot.uri) {
+      skreq[keys.compilerargs] = compileCommand.compilerArgs
+    }
+
+    let dict = try await self.sourcekitd.send(skreq, fileContents: snapshot.text)
+
+    guard
+      let results: SKDResponseArray = dict[self.keys.results]
+    else {
+      throw ResponseError.internalError("sourcekitd response did not contain results or name")
+    }
+
+    try Task.checkCancellation()
+
+    var relatedIdentifiers: [RelatedIdentifier] = []
+
+    results.forEach { _, value in
+      if let offset: Int = value[keys.offset],
+        let start: Position = snapshot.positionOf(utf8Offset: offset),
+        let length: Int = value[keys.length],
+        let end: Position = snapshot.positionOf(utf8Offset: offset + length)
+      {
+        relatedIdentifiers.append(RelatedIdentifier(range: start..<end))
+      }
+      return true
+    }
+    return RelatedIdentifiersResponse(relatedIdentifiers: relatedIdentifiers)
+  }
+}

Sources/SourceKitLSP/Swift/SwiftLanguageServer.swift

@@ -615,49 +615,17 @@ extension SwiftLanguageServer {
   public func documentSymbolHighlight(_ req: DocumentHighlightRequest) async throws -> [DocumentHighlight]? {
     let snapshot = try self.documentManager.latestSnapshot(req.textDocument.uri)
 
-    guard let offset = snapshot.utf8Offset(of: req.position) else {
-      logger.error("invalid position \(req.position, privacy: .public)")
-      return nil
-    }
-
-    let skreq = SKDRequestDictionary(sourcekitd: self.sourcekitd)
-    skreq[keys.request] = self.requests.relatedidents
-    skreq[keys.cancelOnSubsequentRequest] = 0
-    skreq[keys.offset] = offset
-    skreq[keys.sourcefile] = snapshot.uri.pseudoPath
-
-    // FIXME: SourceKit should probably cache this for us.
-    if let compileCommand = await self.buildSettings(for: snapshot.uri) {
-      skreq[keys.compilerargs] = compileCommand.compilerArgs
-    }
-
-    let dict = try await self.sourcekitd.send(skreq, fileContents: snapshot.text)
-
-    guard let results: SKDResponseArray = dict[self.keys.results] else {
-      return []
-    }
-
-    try Task.checkCancellation()
-
-    var highlights: [DocumentHighlight] = []
-
-    results.forEach { _, value in
-      if let offset: Int = value[self.keys.offset],
-        let start: Position = snapshot.positionOf(utf8Offset: offset),
-        let length: Int = value[self.keys.length],
-        let end: Position = snapshot.positionOf(utf8Offset: offset + length)
-      {
-        highlights.append(
-          DocumentHighlight(
-            range: start..<end,
-            kind: .read  // unknown
-          )
-        )
-      }
-      return true
+    let relatedIdentifiers = try await self.relatedIdentifiers(
+      at: req.position,
+      in: snapshot,
+      includeNonEditableBaseNames: false
+    )
+    return relatedIdentifiers.relatedIdentifiers.map {
+      DocumentHighlight(
+        range: $0.range,
+        kind: .read  // unknown
+      )
     }
-
-    return highlights
   }
 
   public func foldingRange(_ req: FoldingRangeRequest) async throws -> [FoldingRange]? {