Reverts "Write an identical value to bin/cache/engine.stamp to prepare for migration (#164317)" (#164396)

<!-- start_original_pr_link -->
Reverts: flutter/flutter#164317
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: matanlurey
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: `bin/cache` does not exist on a fresh checkout,
and `echo bin/cache/...` will fail as a result.

This blocked the google3 roll, but would also break new checkouts of
Flutter, for regular users/contributors.
<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: matanlurey
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {jtmcdole}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
Towards https://github.com/flutter/flutter/issues/164315.

This PR just writes `bin/cache/engine.stamp` identically to how
`bin/internal/engine.version` would otherwise be written, with a caveat
that _if_ `engine.version` is tracked, it is now _copied_ to
`bin/cache/engine.stamp`.

After this lands, I'll send PRs to update tooling that looks for
`engine.version` and give a heads up to the larger team (i.e. Dart HH
bot or whomever we will break by doing this).
<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <flutter-engprod-team@google.com>

.gitignore

@@ -1,6 +1,9 @@
 # Do not remove or rename entries in this file, only add new ones
 # See https://github.com/flutter/flutter/issues/128635 for more context.
 
+# This is dynamic in a monorepo
+bin/internal/engine.version
+
 # Miscellaneous
 *.class
 *.lock
@@ -30,8 +33,6 @@
 /bin/cache/
 /bin/internal/bootstrap.bat
 /bin/internal/bootstrap.sh
-/bin/internal/engine.realm
-/bin/internal/engine.version
 /bin/mingit/
 /dev/benchmarks/mega_gallery/
 /dev/bots/.recipe_deps

bin/internal/update_engine_version.ps1

@@ -22,7 +22,6 @@ $flutterRoot = (Get-Item $progName).parent.parent.FullName
 # On stable, beta, and release tags, the engine.version is tracked by git - do not override it.
 $trackedEngine = (git -C "$flutterRoot" ls-files bin/internal/engine.version) | Out-String
 if ($trackedEngine.length -ne 0) {
-  Copy-Item -Path "$flutterRoot\bin\internal\engine.version" -Destination "$flutterRoot\bin\cache\engine.stamp" -Force
   return
 }
 
@@ -60,17 +59,9 @@ if ([string]::IsNullOrEmpty($engineVersion) -and (Test-Path "$flutterRoot\DEPS"
 
 # Write the engine version out so downstream tools know what to look for.
 $utf8NoBom = New-Object System.Text.UTF8Encoding($false)
-[System.IO.File]::WriteAllText("$flutterRoot\bin\cache\engine.stamp", $engineVersion, $utf8NoBom)
-# TODO(matanlurey): Stop writing to internal/engine.version. https://github.com/flutter/flutter/issues/164315.
 [System.IO.File]::WriteAllText("$flutterRoot\bin\internal\engine.version", $engineVersion, $utf8NoBom)
 
 # The realm on CI is passed in.
 if ($Env:FLUTTER_REALM) {
-    [System.IO.File]::WriteAllText("$flutterRoot\bin\cache\engine.realm", $Env:FLUTTER_REALM, $utf8NoBom)
-    # TODO(matanlurey): Stop writing to internal/engine.realm. https://github.com/flutter/flutter/issues/164315.
     [System.IO.File]::WriteAllText("$flutterRoot\bin\internal\engine.realm", $Env:FLUTTER_REALM, $utf8NoBom)
-} else {
+}
-    [System.IO.File]::WriteAllText("$flutterRoot\bin\cache\engine.realm", "", $utf8NoBom)
-    # TODO(matanlurey): Stop writing to internal/engine.realm. https://github.com/flutter/flutter/issues/164315.
-    [System.IO.File]::WriteAllText("$flutterRoot\bin\internal\engine.realm", "", $utf8NoBom)
-}

bin/internal/update_engine_version.sh

@@ -36,7 +36,6 @@ FLUTTER_ROOT="$(dirname "$(dirname "$(dirname "${BASH_SOURCE[0]}")")")"
 # On stable, beta, and release tags, the engine.version is tracked by git - do not override it.
 TRACKED_ENGINE="$(git -C "$FLUTTER_ROOT" ls-files bin/internal/engine.version)"
 if [[ -n "$TRACKED_ENGINE" ]]; then
-  cp $FLUTTER_ROOT/bin/internal/engine.version $FLUTTER_ROOT/bin/cache/engine.stamp
   exit
 fi
 
@@ -61,17 +60,9 @@ if [ -z "$ENGINE_VERSION" ] && [ -f "$FLUTTER_ROOT/DEPS" ] && [ -f "$FLUTTER_ROO
 fi
 
 # Write the engine version out so downstream tools know what to look for.
-echo $ENGINE_VERSION > "$FLUTTER_ROOT/bin/cache/engine.stamp"
-# TODO(matanlurey): Stop writing to internal/engine.version. https://github.com/flutter/flutter/issues/164315.
 echo $ENGINE_VERSION > "$FLUTTER_ROOT/bin/internal/engine.version"
 
 # The realm on CI is passed in.
 if [ -n "${FLUTTER_REALM}" ]; then
-  echo $FLUTTER_REALM > "$FLUTTER_ROOT/bin/cache/engine.realm"
-  # TODO(matanlurey): Stop writing to internal/engine.realm. https://github.com/flutter/flutter/issues/164315.
   echo $FLUTTER_REALM > "$FLUTTER_ROOT/bin/internal/engine.realm"
-else
-  echo "" > "$FLUTTER_ROOT/bin/cache/engine.realm"
-  # TODO(matanlurey): Stop writing to internal/engine.realm. https://github.com/flutter/flutter/issues/164315.
-  echo "" > "$FLUTTER_ROOT/bin/internal/engine.realm"
 fi

dev/tools/test/update_engine_version_test.dart

@@ -58,7 +58,6 @@ void main() {
   setUp(() async {
     tmpDir = localFs.systemTempDirectory.createTempSync('update_engine_version_test.');
     testRoot = _FlutterRootUnderTest.fromPath(tmpDir.childDirectory('flutter').path);
-    testRoot.root.childDirectory('bin').childDirectory('cache').createSync(recursive: true);
 
     environment = <String, String>{};
     environment.addAll(io.Platform.environment);
@@ -71,56 +70,7 @@ void main() {
   });
 
   tearDown(() {
-    // Git adds a lot of files, we don't want to test for them.
-    final Directory gitDir = testRoot.root.childDirectory('.git');
-    if (gitDir.existsSync()) {
-      gitDir.deleteSync(recursive: true);
-    }
-
-    // Take a snapshot of files we expect to be created or otherwise exist.
-    //
-    // This gives a "dirty" check that we did not change the output characteristics
-    // of the tool without adding new tests for the new files.
-    final Set<String> expectedFiles = <String>{
-      localFs.path.join('bin', 'cache', 'engine.realm'),
-      localFs.path.join('bin', 'cache', 'engine.stamp'),
-      localFs.path.join(
-        'bin',
-        'internal',
-        localFs.path.basename(testRoot.binInternalUpdateEngineVersion.path),
-      ),
-      localFs.path.join('bin', 'internal', 'engine.realm'),
-      localFs.path.join('bin', 'internal', 'engine.version'),
-      localFs.path.join('engine', 'src', '.gn'),
-      'DEPS',
-    };
-    final Set<String> currentFiles =
-        tmpDir
-            .listSync(recursive: true)
-            .whereType<File>()
-            .map((File e) => localFs.path.relative(e.path, from: testRoot.root.path))
-            .toSet();
-
-    // If this test failed, print out the current directory structure.
-    printOnFailure(
-      'Files in virtual "flutter" directory when test failed: ${(currentFiles.toList()..sort()).join('\n')}',
-    );
-
-    // Now do cleanup so even if the next step fails, we still deleted tmp.
     tmpDir.deleteSync(recursive: true);
-
-    final Set<String> unexpectedFiles = currentFiles.difference(expectedFiles);
-    if (unexpectedFiles.isNotEmpty) {
-      final StringBuffer message = StringBuffer(
-        'One or more files were generated by ${localFs.path.basename(testRoot.binInternalUpdateEngineVersion.path)} that were not expected:\n\n',
-      );
-      message.writeAll(unexpectedFiles, '\n');
-      message.writeln('\n');
-      message.writeln(
-        'If this was intentional update "expectedFiles" in dev/tools/test/update_engine_version_test.dart and add *new* tests for the new outputs.',
-      );
-      fail('$message');
-    }
   });
 
   io.ProcessResult runUpdateEngineVersion() {
@@ -170,7 +120,6 @@ void main() {
         testRoot.binInternalEngineVersion.readAsStringSync(),
         equalsIgnoringWhitespace('123abc'),
       );
-      expect(testRoot.binCacheEngineStamp.readAsStringSync(), equalsIgnoringWhitespace('123abc'));
     });
   });
 
@@ -186,10 +135,6 @@ void main() {
       testRoot.binInternalEngineVersion.readAsStringSync(),
       equalsIgnoringWhitespace(engineVersionTrackedContents),
     );
-    expect(
-      testRoot.binCacheEngineStamp.readAsStringSync(),
-      equalsIgnoringWhitespace(engineVersionTrackedContents),
-    );
   });
 
   test('writes nothing, even if files are set, if we are on "3.29.0"', () async {
@@ -204,10 +149,6 @@ void main() {
       testRoot.binInternalEngineVersion.readAsStringSync(),
       equalsIgnoringWhitespace(engineVersionTrackedContents),
     );
-    expect(
-      testRoot.binCacheEngineStamp.readAsStringSync(),
-      equalsIgnoringWhitespace(engineVersionTrackedContents),
-    );
   });
 
   test('writes nothing, even if files are set, if we are on "beta"', () async {
@@ -222,10 +163,6 @@ void main() {
       testRoot.binInternalEngineVersion.readAsStringSync(),
       equalsIgnoringWhitespace(engineVersionTrackedContents),
     );
-    expect(
-      testRoot.binCacheEngineStamp.readAsStringSync(),
-      equalsIgnoringWhitespace(engineVersionTrackedContents),
-    );
   });
 
   group('if DEPS and engine/src/.gn are present, engine.version is derived from', () {
@@ -248,10 +185,6 @@ void main() {
         testRoot.binInternalEngineVersion.readAsStringSync(),
         equalsIgnoringWhitespace(mergeBaseHeadUpstream.stdout as String),
       );
-      expect(
-        testRoot.binCacheEngineStamp.readAsStringSync(),
-        equalsIgnoringWhitespace(mergeBaseHeadUpstream.stdout as String),
-      );
     });
 
     test('merge-base HEAD origin/master on non-LUCI when upstream is not set', () async {
@@ -269,10 +202,6 @@ void main() {
         testRoot.binInternalEngineVersion.readAsStringSync(),
         equalsIgnoringWhitespace(mergeBaseHeadOrigin.stdout as String),
       );
-      expect(
-        testRoot.binCacheEngineStamp.readAsStringSync(),
-        equalsIgnoringWhitespace(mergeBaseHeadOrigin.stdout as String),
-      );
     });
 
     test('rev-parse HEAD when running on LUCI', () async {
@@ -285,10 +214,6 @@ void main() {
         testRoot.binInternalEngineVersion.readAsStringSync(),
         equalsIgnoringWhitespace(revParseHead.stdout as String),
       );
-      expect(
-        testRoot.binCacheEngineStamp.readAsStringSync(),
-        equalsIgnoringWhitespace(revParseHead.stdout as String),
-      );
     });
   });
 
@@ -308,7 +233,6 @@ void main() {
 
       expect(testRoot.binInternalEngineVersion, exists);
       expect(testRoot.binInternalEngineVersion.readAsStringSync(), equalsIgnoringWhitespace(''));
-      expect(testRoot.binCacheEngineStamp.readAsStringSync(), equalsIgnoringWhitespace(''));
     });
 
     test('[engine/src/.gn] engine.version is blank', () async {
@@ -318,45 +242,6 @@ void main() {
 
       expect(testRoot.binInternalEngineVersion, exists);
       expect(testRoot.binInternalEngineVersion.readAsStringSync(), equalsIgnoringWhitespace(''));
-      expect(testRoot.binCacheEngineStamp.readAsStringSync(), equalsIgnoringWhitespace(''));
-    });
-  });
-
-  group('engine.realm', () {
-    setUp(() {
-      for (final File f in <File>[testRoot.deps, testRoot.engineSrcGn]) {
-        f.createSync(recursive: true);
-      }
-      setupRepo(branch: 'master');
-      setupRemote(remote: 'origin');
-    });
-
-    test('is empty if the FLUTTER_REALM environment variable is not set', () {
-      expect(environment, isNot(contains('FLUTTER_REALM')));
-
-      runUpdateEngineVersion();
-
-      expect(testRoot.binCacheEngineRealm, exists);
-      expect(testRoot.binCacheEngineRealm.readAsStringSync(), equalsIgnoringWhitespace(''));
-      expect(testRoot.binInternalEngineRealm, exists);
-      expect(testRoot.binInternalEngineRealm.readAsStringSync(), equalsIgnoringWhitespace(''));
-    });
-
-    test('contains the FLUTTER_REALM environment variable', () async {
-      environment['FLUTTER_REALM'] = 'flutter_archives_v2';
-
-      runUpdateEngineVersion();
-
-      expect(testRoot.binCacheEngineRealm, exists);
-      expect(
-        testRoot.binCacheEngineRealm.readAsStringSync(),
-        equalsIgnoringWhitespace('flutter_archives_v2'),
-      );
-      expect(testRoot.binInternalEngineRealm, exists);
-      expect(
-        testRoot.binInternalEngineRealm.readAsStringSync(),
-        equalsIgnoringWhitespace('flutter_archives_v2'),
-      );
     });
   });
 }
@@ -394,11 +279,9 @@ final class _FlutterRootUnderTest {
       binInternalEngineVersion: root.childFile(
         fileSystem.path.join('bin', 'internal', 'engine.version'),
       ),
-      binCacheEngineRealm: root.childFile(fileSystem.path.join('bin', 'cache', 'engine.realm')),
       binInternalEngineRealm: root.childFile(
         fileSystem.path.join('bin', 'internal', 'engine.realm'),
       ),
-      binCacheEngineStamp: root.childFile(fileSystem.path.join('bin', 'cache', 'engine.stamp')),
       binInternalUpdateEngineVersion: root.childFile(
         fileSystem.path.join(
           'bin',
@@ -428,9 +311,7 @@ final class _FlutterRootUnderTest {
     this.root, {
     required this.deps,
     required this.engineSrcGn,
-    required this.binCacheEngineStamp,
     required this.binInternalEngineVersion,
-    required this.binCacheEngineRealm,
     required this.binInternalEngineRealm,
     required this.binInternalUpdateEngineVersion,
   });
@@ -450,35 +331,13 @@ final class _FlutterRootUnderTest {
   /// `bin/internal/engine.version`.
   ///
   /// This file contains a SHA of which engine binaries to download.
-  ///
+  final File binInternalEngineVersion;
-  /// Currently, the SHA is either _computed_ or _pre-determined_, based on if
-  /// the file is checked-in and tracked. That behavior is changing, and in the
-  /// future this will be a checked-in file and not computed.
-  ///
-  /// See also: https://github.com/flutter/flutter/issues/164315.
-  final File binInternalEngineVersion; // TODO(matanlurey): Update these docs.
-
-  /// `bin/cache/engine.stamp`.
-  ///
-  /// This file contains a _computed_ SHA of which engine binaries to download.
-  final File binCacheEngineStamp;
 
   /// `bin/internal/engine.realm`.
   ///
-  /// If non-empty, the value comes from the environment variable `FLUTTER_REALM`,
+  /// It is a mystery what this file contains, but it's set by `FLUTTER_REALM`.
-  /// which instructs the tool where the SHA stored in [binInternalEngineVersion]
-  /// should be fetched from (it differs for presubmits run for flutter/flutter
-  /// and builds downloaded by end-users or by postsubmits).
   final File binInternalEngineRealm;
 
-  /// `bin/cache/engine.realm`.
-  ///
-  /// If non-empty, the value comes from the environment variable `FLUTTER_REALM`,
-  /// which instructs the tool where the SHA stored in [binInternalEngineVersion]
-  /// should be fetched from (it differs for presubmits run for flutter/flutter
-  /// and builds downloaded by end-users or by postsubmits).
-  final File binCacheEngineRealm;
-
   /// `bin/internal/update_engine_version.{sh|ps1}`.
   ///
   /// This file contains a shell script that conditionally writes, on execution: