Migrate status file entries when migrating files. Yay!

tools/migration/lib/src/fork.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 
 import 'io.dart';
 import 'log.dart';
+import 'test_directories.dart';
 import 'validate.dart';
 
 /// Tracks one test and the various forked locations where it may appear.
 ///
 /// * "One" refers to the original Dart 1.0 location of the test: language/,
 ///   corelib/, etc.
 ///
 /// * "Strong" is the DDC fork of the file: language_strong, etc.
 ///
 /// * "Two" is the migrated 2.0 destination location: language_2, etc.
 class Fork {
   final String twoPath;
-  String onePath;
-  String strongPath;
+  String get onePath => toOnePath(twoPath);
+  String get strongPath => toStrongPath(twoPath);
 
   String get twoSource {
     if (twoPath == null) return null;
     if (_twoSource == null) _twoSource = readFile(twoPath);
     return _twoSource;
   }
 
   String _twoSource;
 
   String get oneSource {
     if (onePath == null) return null;
     if (_oneSource == null) _oneSource = readFile(onePath);
     return _oneSource;
   }
 
   String _oneSource;
 
   String get strongSource {
     if (strongPath == null) return null;
     if (_strongSource == null) _strongSource = readFile(strongPath);
     return _strongSource;
   }
 
-  bool get isMigrated => new File(p.join(testRoot, twoPath)).existsSync();
+  bool get oneExists => new File(p.join(testRoot, onePath)).existsSync();
+  bool get strongExists => new File(p.join(testRoot, strongPath)).existsSync();
+  bool get twoExists => new File(p.join(testRoot, twoPath)).existsSync();
 
   String _strongSource;
 
   Fork(this.twoPath);
 
   List<String> migrate() {
     print("- ${bold(twoPath)}:");
 
     var todos = <String>[];
 
-    if (onePath == null && strongPath == null) {
+    if (!oneExists && !twoExists) {
       // It's already been migrated, so there's nothing to move.
       note("Is already migrated.");
-    } else if (isMigrated) {
+    } else if (twoExists) {
       // If there is a migrated version and it's the same as an unmigrated one,
       // delete the unmigrated one.
-      if (onePath != null) {
+      if (oneExists) {
         if (oneSource == twoSource) {
           deleteFile(onePath);
           done("Deleted already-migrated $onePath.");
         } else {
           note("${bold(onePath)} does not match already-migrated file.");
           todos.add("Merge from ${bold(onePath)} into this file.");
           validateFile(onePath, oneSource);
         }
       }
 
-      if (strongPath != null) {
+      if (strongExists) {
         if (strongSource == twoSource) {
           deleteFile(strongPath);
           done("Deleted already-migrated ${bold(strongPath)}.");
         } else {
           note("${bold(strongPath)} does not match already-migrated file.");
           todos.add("Merge from ${bold(strongPath)} into this file.");
           validateFile(strongPath, strongSource);
         }
       }
     } else {
-      if (strongPath == null) {
+      if (!strongExists) {
         // If it only exists in one place, just move it.
         moveFile(onePath, twoPath);
         done("Moved from ${bold(onePath)} (no strong mode fork).");
-      } else if (onePath == null) {
+      } else if (!oneExists) {
         // If it only exists in one place, just move it.
         moveFile(strongPath, twoPath);
         done("Moved from ${bold(strongPath)} (no 1.0 mode fork).");
       } else if (oneSource == strongSource) {
         // The forks are identical, pick one.
         moveFile(onePath, twoPath);
         deleteFile(strongPath);
         done("Merged identical forks.");
         validateFile(twoPath, oneSource);
       } else {
         // Otherwise, a manual merge is required. Start with the strong one.
         moveFile(strongPath, twoPath);
         done("Moved strong fork, kept 1.0 fork, manual merge required.");
         todos.add("Merge from ${bold(onePath)} into this file.");
         validateFile(onePath, oneSource);
       }
     }
 
     // See what work is left to be done in the migrated file.
-    if (isMigrated) {
+    if (twoExists) {
       validateFile(twoPath, twoSource, todos);
     }
 
     return todos;
   }
 }