Use realpath from the tests to do symlink resolution.

Author: allevato

Sources/SwiftFormat/Utilities/FileIterator.swift

@@ -168,32 +168,41 @@ public struct FileIterator: Sequence, IteratorProtocol {
 ///   exist or is not a supported file type. If `followSymlinks` is `true`, the returned URL may be
 ///   different from the given URL; otherwise, it will be the same.
 private func fileAndType(at url: URL, followSymlinks: Bool) -> (URL, FileAttributeType)? {
-  func typeOfFile(at url: URL) -> FileAttributeType? {
-    // We cannot use `URL.resourceValues(forKeys:)` here because it appears to behave incorrectly on
-    // Linux.
-    return try? FileManager.default.attributesOfItem(atPath: url.path)[.type] as? FileAttributeType
+  var url = url
+  if followSymlinks {
+    url = realPath(of: url)
   }
 
-  guard var fileType = typeOfFile(at: url) else {
+  // We cannot use `URL.resourceValues(forKeys:)` here because it appears to behave incorrectly on
+  // Linux.
+  guard
+    let type =
+      try? FileManager.default.attributesOfItem(atPath: url.path)[.type] as? FileAttributeType
+  else {
     return nil
   }
 
-  // We would use `standardizedFileURL.path` here as we do in the iterator above to ensure that
-  // path components like `.` and `..` are resolved, but the standardized URLs returned by
-  // Foundation pre-Swift-6.0 resolve symlinks. This causes the file type of a URL and its
-  // standardized path to not match.
-  var visited: Set<String> = [url.absoluteString]
-  var url = url
-  while followSymlinks && fileType == .typeSymbolicLink,
-    let destination = try? FileManager.default.destinationOfSymbolicLink(atPath: url.path)
-  {
-    url = URL(fileURLWithPath: destination, relativeTo: url)
-    // If this URL is in the visited set, we must have a symlink cycle. Ignore it gracefully.
-    guard !visited.contains(url.absoluteString), let newType = typeOfFile(at: url) else {
-      return nil
+  return (url, type)
+}
+
+/// Assuming the given URL is a file URL, resolves all symlinks in its path.
+///
+/// - Note: We need this because `URL.resolvingSymlinksInPath()` not only resolves symlinks but also standardizes the
+///   path by stripping away `private` prefixes.
+@_spi(Internal)
+public func realPath(of url: URL) -> URL {
+  #if canImport(Darwin)
+  return url.path.withCString { path in
+    guard let realpath = Darwin.realpath(path, nil) else {
+      return url
     }
-    visited.insert(url.absoluteString)
-    fileType = newType
+    let result = URL(fileURLWithPath: String(cString: realpath))
+    free(realpath)
+    return result
   }
-  return (url, fileType)
+  #else
+  // Non-Darwin platforms don't have the `/private` stripping issue, so we can just use `self.resolvingSymlinksInPath`
+  // here.
+  return url.resolvingSymlinksInPath()
+  #endif
 }

Tests/SwiftFormatTests/Utilities/FileIteratorTests.swift

@@ -1,41 +1,18 @@
 @_spi(Internal) @_spi(Testing) import SwiftFormat
 import XCTest
 
-extension URL {
-  /// Assuming this is a file URL, resolves all symlinks in the path.
-  ///
-  /// - Note: We need this because `URL.resolvingSymlinksInPath()` not only resolves symlinks but also standardizes the
-  ///   path by stripping away `private` prefixes. Since sourcekitd is not performing this standardization, using
-  ///   `resolvingSymlinksInPath` can lead to slightly mismatched URLs between the sourcekit-lsp response and the test
-  ///   assertion.
-  fileprivate var realpath: URL {
-    #if canImport(Darwin)
-    return self.path.withCString { path in
-      guard let realpath = Darwin.realpath(path, nil) else {
-        return self
-      }
-      let result = URL(fileURLWithPath: String(cString: realpath))
-      free(realpath)
-      return result
-    }
-    #else
-    // Non-Darwin platforms don't have the `/private` stripping issue, so we can just use `self.resolvingSymlinksInPath`
-    // here.
-    return self.resolvingSymlinksInPath()
-    #endif
-  }
-}
-
 final class FileIteratorTests: XCTestCase {
   private var tmpdir: URL!
 
   override func setUpWithError() throws {
-    tmpdir = try FileManager.default.url(
-      for: .itemReplacementDirectory,
-      in: .userDomainMask,
-      appropriateFor: FileManager.default.temporaryDirectory,
-      create: true
-    ).realpath
+    tmpdir = realPath(
+      of: try FileManager.default.url(
+        for: .itemReplacementDirectory,
+        in: .userDomainMask,
+        appropriateFor: FileManager.default.temporaryDirectory,
+        create: true
+      )
+    )
 
     // Create a simple file tree used by the tests below.
     try touch("project/real1.swift")