Clean up the semantics of io.dart operations w.r.t. symlinks.

utils/pub/io.dart

Index: utils/pub/io.dart
diff --git a/utils/pub/io.dart b/utils/pub/io.dart
index f4bb6de9e243da207bf8cd92126f792fea4efc90..a32c4714198b4e94c7e8969d3f1202177721bc63 100644
--- a/utils/pub/io.dart
+++ b/utils/pub/io.dart
@@ -28,12 +28,16 @@ bool isBeneath(String entry, String dir) {
 }
 
 /// Determines if a file or directory exists at [path].
-bool entryExists(String path) => dirExists(path) || fileExists(path);
+bool entryExists(String path) =>
+  dirExists(path) || fileExists(path) || linkExists(path);
 
-/// Determines if [file] exists on the file system. Will also return `true` if
-/// [file] points to a symlink, even a directory symlink.
-bool fileExists(String file) =>
-    new File(file).existsSync() || new Link(file).existsSync();
+/// Returns whether [link] exists on the file system. This will return `true`
+/// for any symlink, regardless of what it points at or whether it's broken.
+bool linkExists(String path) => new Link(path).existsSync();
+
+/// Returns whether [file] exists on the file system. This will return `true`
+/// for a symlink only if that symlink is unbroken and points to a file.
+bool fileExists(String file) => new File(file).existsSync();
 
 /// Reads the contents of the text file [file].
 String readTextFile(String file) =>
@@ -61,11 +65,6 @@ String writeTextFile(String file, String contents, {dontLogContents: false}) {
   return file;
 }
 
-/// Deletes [file].
-void deleteFile(String file) {
-  new File(file).deleteSync();
-}
-
 /// Creates [file] and writes [contents] to it.
 String writeBinaryFile(String file, List<int> contents) {
   log.io("Writing ${contents.length} bytes to binary file $file.");
@@ -126,12 +125,6 @@ String createTempDir([dir = '']) {
   return tempDir.path;
 }
 
-/// Recursively deletes [dir].
-void deleteDir(String dir) {
-  log.io("Deleting directory $dir.");
-  new Directory(dir).deleteSync(recursive: true);
-}
-
 /// Asynchronously lists the contents of [dir]. If [recursive] is `true`, lists
 /// subdirectory contents (defaults to `false`). If [includeHiddenFiles] is
 /// `true`, includes files and directories beginning with `.` (defaults to
@@ -199,21 +192,29 @@ Future<List<String>> listDir(String dir,
   return doList(dir, new Set<String>());
 }
 
-/// Determines if [dir] exists on the file system.
+/// Returns whether [dir] exists on the file system. This will return `true` for
+/// a symlink only if that symlink is unbroken and points to a directory.
 bool dirExists(String dir) => new Directory(dir).existsSync();
 
+/// Deletes whatever's at [path], whether it's a file, directory, or symlink. If
+/// it's a directory, it will be deleted recursively.
+void deleteEntry(String path) {
+  if (linkExists(path)) {
+    log.io("Deleting link $path.");
+    new Link(path).deleteSync();
+  } else if (dirExists(path)) {
+    log.io("Deleting directory $path.");
+    new Directory(path).deleteSync(recursive: true);
+  } else {
+    log.io("Deleting file $path.");
+    new File(path).deleteSync();
+  }
+}
+
 /// "Cleans" [dir]. If that directory already exists, it will be deleted. Then a
 /// new empty directory will be created.
 void cleanDir(String dir) {
-  if (dirExists(dir)) {
-    // Delete it first.
-    deleteDir(dir);
-  } else if (fileExists(dir)) {
-    // If there is a non-directory there (file or symlink), delete it.
-    deleteFile(dir);
-  }
-
-  // Just create it.
+  if (entryExists(dir)) deleteEntry(dir);
   createDir(dir);
 }
 
@@ -582,7 +583,7 @@ Future withTempDir(Future fn(String path)) {
   return defer(() {
     var tempDir = createTempDir();
     return new Future.of(() => fn(tempDir))
-        .whenComplete(() => deleteDir(tempDir));
+        .whenComplete(() => deleteEntry(tempDir));
   });
 }