Support cursor info-based requests when cursor is placed at the end of an identifier

VS Code considers the position after an identifier as part of an identifier. Ie. if you have `let foo| = 1`, then it considers the cursor to be positioned at the identifier. This scenario is hit, when selecting an identifier by double-clicking it and then eg. performing jump-to-definition. In that case VS Code will send the position after the identifier.
`sourcekitd`, on the other hand, does not consider the position after the identifier as part of the identifier.
To bridge the gap here, normalize any positions inside, or directly after, an identifier to the identifier's start.

Fixes #820
rdar://115557453

Author: ahoppen

Sources/SourceKitLSP/CMakeLists.txt

@@ -29,6 +29,7 @@ target_sources(SourceKitLSP PRIVATE
   Swift/SourceKitD+ResponseError.swift
   Swift/SwiftCommand.swift
   Swift/SwiftLanguageServer.swift
+  Swift/SymbolInfo.swift
   Swift/SyntaxHighlightingToken.swift
   Swift/SyntaxHighlightingTokenParser.swift
   Swift/SyntaxTreeManager.swift

Sources/SourceKitLSP/Swift/SwiftLanguageServer.swift

@@ -540,15 +540,6 @@ extension SwiftLanguageServer {
     return HoverResponse(contents: .markupContent(MarkupContent(kind: .markdown, value: result)), range: nil)
   }
 
-  public func symbolInfo(_ req: SymbolInfoRequest) async throws -> [SymbolDetails] {
-    let uri = req.textDocument.uri
-    let position = req.position
-    guard let cursorInfo = try await cursorInfo(uri, position..<position) else {
-      return []
-    }
-    return [cursorInfo.symbolInfo]
-  }
-
   public func documentColor(_ req: DocumentColorRequest) async throws -> [ColorInformation] {
     let snapshot = try self.documentManager.latestSnapshot(req.textDocument.uri)
 
@@ -1222,6 +1213,13 @@ extension DocumentSnapshot {
     return lowerBound..<upperBound
   }
 
+  func position(of position: Position) -> AbsolutePosition? {
+    guard let offset = utf8Offset(of: position) else {
+      return nil
+    }
+    return AbsolutePosition(utf8Offset: offset)
+  }
+
   func indexOf(utf8Offset: Int) -> String.Index? {
     return text.utf8.index(text.startIndex, offsetBy: utf8Offset, limitedBy: text.endIndex)
   }

Sources/SourceKitLSP/Swift/SymbolInfo.swift

@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 LanguageServerProtocol
+import SwiftSyntax
+
+fileprivate class StartOfIdentifierFinder: SyntaxAnyVisitor {
+  let requestedPosition: AbsolutePosition
+  var resolvedPosition: AbsolutePosition?
+
+  init(position: AbsolutePosition) {
+    self.requestedPosition = position
+    super.init(viewMode: .sourceAccurate)
+  }
+
+  override func visitAny(_ node: Syntax) -> SyntaxVisitorContinueKind {
+    if (node.position...node.endPosition).contains(requestedPosition) {
+      return .visitChildren
+    } else {
+      return .skipChildren
+    }
+  }
+
+  override func visit(_ token: TokenSyntax) -> SyntaxVisitorContinueKind {
+    if token.tokenKind.isPunctuation || token.tokenKind == .endOfFile {
+      return .skipChildren
+    }
+    if (token.positionAfterSkippingLeadingTrivia...token.endPositionBeforeTrailingTrivia).contains(requestedPosition) {
+      self.resolvedPosition = token.positionAfterSkippingLeadingTrivia
+    }
+    return .skipChildren
+  }
+}
+
+extension SwiftLanguageServer {
+  /// VS Code considers the position after an identifier as part of an identifier. Ie. if you have `let foo| = 1`, then
+  /// it considers the cursor to be positioned at the identifier. This scenario is hit, when selecting an identifier by
+  /// double-clicking it and then eg. performing jump-to-definition. In that case VS Code will send the position after
+  /// the identifier.
+  /// `sourcekitd`, on the other hand, does not consider the position after the identifier as part of the identifier.
+  /// To bridge the gap here, normalize any positions inside, or directly after, an identifier to the identifier's
+  /// start.
+  private func adjustPositionToStartOfIdentifier(
+    _ position: Position,
+    in snapshot: DocumentSnapshot
+  ) async -> Position {
+    let tree = await self.syntaxTreeManager.syntaxTree(for: snapshot)
+    guard let swiftSyntaxPosition = snapshot.position(of: position) else {
+      return position
+    }
+    let visitor = StartOfIdentifierFinder(position: swiftSyntaxPosition)
+    visitor.walk(tree)
+    if let resolvedPosition = visitor.resolvedPosition {
+      return snapshot.position(of: resolvedPosition) ?? position
+    } else {
+      return position
+    }
+  }
+
+  public func symbolInfo(_ req: SymbolInfoRequest) async throws -> [SymbolDetails] {
+    let uri = req.textDocument.uri
+    let snapshot = try documentManager.latestSnapshot(uri)
+    let position = await self.adjustPositionToStartOfIdentifier(req.position, in: snapshot)
+    guard let cursorInfo = try await cursorInfo(uri, position..<position) else {
+      return []
+    }
+    return [cursorInfo.symbolInfo]
+  }
+}

Tests/SourceKitLSPTests/DefinitionTests.swift

@@ -0,0 +1,39 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 LanguageServerProtocol
+import SKTestSupport
+import XCTest
+
+class DefinitionTests: XCTestCase {
+  func testJumpToDefinitionAtEndOfIdentifier() async throws {
+    let testClient = try await TestSourceKitLSPClient()
+    let uri = DocumentURI.for(.swift)
+
+    let positions = testClient.openDocument(
+      """
+      let 1️⃣foo = 1
+      _ = foo2️⃣
+      """,
+      uri: uri
+    )
+
+    let response = try await testClient.send(
+      DefinitionRequest(textDocument: TextDocumentIdentifier(uri), position: positions["2️⃣"])
+    )
+    guard case .locations(let locations) = response else {
+      XCTFail("Expected locations response")
+      return
+    }
+    XCTAssertEqual(locations, [Location(uri: uri, range: Range(positions["1️⃣"]))])
+  }
+}