Don’t enter an infinite loop when a circular symlink is added to a project

Author: ahoppen

Sources/SemanticIndex/CheckedIndex.swift

@@ -341,11 +341,14 @@ private struct IndexOutOfDateChecker {
 
   private enum Error: Swift.Error, CustomStringConvertible {
     case fileAttributesDontHaveModificationDate
+    case circularSymlink(URL)
 
     var description: String {
       switch self {
       case .fileAttributesDontHaveModificationDate:
         return "File attributes don't contain a modification date"
+      case .circularSymlink(let url):
+        return "Circular symlink at \(url)"
       }
     }
   }
@@ -484,6 +487,8 @@ private struct IndexOutOfDateChecker {
       }
       var modificationDate = try Self.modificationDate(atPath: fileURL.filePath)
 
+      var visited: Set<URL> = [fileURL]
+
       // Get the maximum mtime in the symlink chain as the modification date of the URI. That way if either the symlink
       // is changed to point to a different file or if the underlying file is modified, the modification time is
       // updated.
@@ -492,6 +497,9 @@ private struct IndexOutOfDateChecker {
       ),
         let symlinkDestination = URL(string: relativeSymlinkDestination, relativeTo: fileURL)
       {
+        if !visited.insert(symlinkDestination).inserted {
+          throw Error.circularSymlink(symlinkDestination)
+        }
         fileURL = symlinkDestination
         modificationDate = max(modificationDate, try Self.modificationDate(atPath: fileURL.filePath))
       }

Tests/SourceKitLSPTests/BackgroundIndexingTests.swift

@@ -2201,6 +2201,24 @@ final class BackgroundIndexingTests: XCTestCase {
       }
     )
   }
+
+  func testCircularSymlink() async throws {
+    let project = try await SwiftPMTestProject(
+      files: [
+        "Symlink.swift": ""
+      ],
+      enableBackgroundIndexing: true
+    )
+    let circularSymlink = try XCTUnwrap(project.uri(for: "Symlink.swift").fileURL)
+    try FileManager.default.removeItem(at: circularSymlink)
+    try FileManager.default.createSymbolicLink(at: circularSymlink, withDestinationURL: circularSymlink)
+
+    project.testClient.send(
+      DidChangeWatchedFilesNotification(changes: [FileEvent(uri: URI(circularSymlink), type: .changed)])
+    )
+    // Check that we don't enter an infinite loop trying to index the circular symlink.
+    try await project.testClient.send(PollIndexRequest())
+  }
 }
 
 extension HoverResponseContents {