From a76f57202e6e27f051874f58a838e2d3134b0896 Mon Sep 17 00:00:00 2001
From: Alex Hoppen <ahoppen@apple.com>
Date: Thu, 13 Mar 2025 21:11:04 -0700
Subject: [PATCH] =?UTF-8?q?Don=E2=80=99t=20enter=20an=20infinite=20loop=20?=
 =?UTF-8?q?when=20a=20circular=20symlink=20is=20added=20to=20a=20project?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 Sources/SemanticIndex/CheckedIndex.swift       |  8 ++++++++
 .../BackgroundIndexingTests.swift              | 18 ++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/Sources/SemanticIndex/CheckedIndex.swift b/Sources/SemanticIndex/CheckedIndex.swift
index 48d849fee..ec6a99036 100644
--- a/Sources/SemanticIndex/CheckedIndex.swift
+++ b/Sources/SemanticIndex/CheckedIndex.swift
@@ -355,11 +355,14 @@ 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)"
       }
     }
   }
@@ -517,6 +520,8 @@ 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.
@@ -524,6 +529,9 @@ private struct IndexOutOfDateChecker {
         atPath: fileURL.filePath
       ) {
         fileURL = URL(fileURLWithPath: relativeSymlinkDestination, relativeTo: fileURL)
+        if !visited.insert(fileURL).inserted {
+          throw Error.circularSymlink(fileURL)
+        }
         modificationDate = max(modificationDate, try Self.modificationDate(atPath: fileURL.filePath))
       }
 
diff --git a/Tests/SourceKitLSPTests/BackgroundIndexingTests.swift b/Tests/SourceKitLSPTests/BackgroundIndexingTests.swift
index 5988cdafa..1aca7fc6c 100644
--- a/Tests/SourceKitLSPTests/BackgroundIndexingTests.swift
+++ b/Tests/SourceKitLSPTests/BackgroundIndexingTests.swift
@@ -2521,6 +2521,24 @@ final class BackgroundIndexingTests: XCTestCase {
     let workspaceSymbolsAfterUpdate = try await project.testClient.send(WorkspaceSymbolsRequest(query: "myTest"))
     XCTAssertEqual(workspaceSymbolsAfterUpdate?.compactMap(\.symbolInformation?.name), ["myTestA_updated", "myTestB"])
   }
+
+  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(SynchronizeRequest(index: true))
+  }
 }
 
 extension HoverResponseContents {