Update pre-commit formatter to use java from repo rather than path. (flutter/engine#54450)

This removes the recently added requirement of contributors having
`java` on their path.

Also removed the mention of java being needed in setup (I don't have
java
installed and have built the engine from mac for years).

Fixes https://github.com/flutter/flutter/issues/152968
Fixes https://github.com/flutter/flutter/issues/129221

DEPS

@@ -799,7 +799,7 @@ deps = {
         'version': 'version:17'
        }
      ],
-     'condition': 'download_android_deps',
+     # Always download the JDK since java is required for running the formatter.
      'dep_type': 'cipd',
    },
 

engine/src/flutter/ci/bin/format.dart

@@ -461,7 +461,7 @@ class ClangFormatChecker extends FormatChecker {
   }
 }
 
-/// Checks the format of Java files uing the Google Java format checker.
+/// Checks the format of Java files using the Google Java format checker.
 class JavaFormatChecker extends FormatChecker {
   JavaFormatChecker({
     super.processManager,
@@ -483,8 +483,31 @@ class JavaFormatChecker extends FormatChecker {
         ),
       ),
     );
+    // Use java from the checkout to avoid contributors needing to install java.
+    final File hermetic = hermeticJava(srcDir);
+    // If for some reason the hermetic java doesn't exist, fall back to the system java.
+    javaExe = hermetic.existsSync() ? hermetic.path : 'java';
   }
 
+  /// Returns the path to the java executable in the flutter repository.
+  static File hermeticJava(Directory srcDir) {
+    final List<String> javaPath = <String>[
+      srcDir.absolute.path,
+      'flutter',
+      'third_party',
+      'java',
+      'openjdk',
+    ];
+    if (Platform.isMacOS) {
+      javaPath.add('Contents');
+      javaPath.add('Home');
+    }
+    javaPath.add('bin');
+    javaPath.add(Platform.isWindows ? 'java.exe' : 'java');
+    return File(path.joinAll(javaPath));
+  }
+
+  late final String javaExe;
   late final File googleJavaFormatJar;
 
   // String to return if java formatting cant check java code for any reson.
@@ -492,7 +515,7 @@ class JavaFormatChecker extends FormatChecker {
 
   Future<String> _getGoogleJavaFormatVersion() async {
     final ProcessRunnerResult result = await _processRunner
-        .runProcess(<String>['java', '-jar', googleJavaFormatJar.path, '--version']);
+        .runProcess(<String>[javaExe, '-jar', googleJavaFormatJar.path, '--version']);
     return result.stderr.trim();
   }
 
@@ -521,7 +544,7 @@ class JavaFormatChecker extends FormatChecker {
 
   Future<String> _getJavaVersion() async {
     final ProcessRunnerResult result =
-        await _processRunner.runProcess(<String>['java', '-version']);
+        await _processRunner.runProcess(<String>[javaExe, '-version']);
     return result.stderr.trim().split('\n')[0];
   }
 
@@ -538,7 +561,12 @@ class JavaFormatChecker extends FormatChecker {
     try {
       javaVersion = await _getJavaVersion();
     } on ProcessRunnerException {
-      error('Cannot run Java, skipping Java file formatting!');
+      if (!_processRunner.processManager.canRun(javaExe)) {
+        error('Cannot find Java ($javaExe). '
+        'Skipping Java format check.');
+        return const <String>[_javaFormatErrorString];
+      }
+      error('Cannot run Java ($javaExe), skipping Java file formatting!');
       return const <String>[_javaFormatErrorString];
     }
     try {
@@ -556,7 +584,7 @@ class JavaFormatChecker extends FormatChecker {
       }
       formatJobs.add(
         WorkerJob(
-          <String>['java', '-jar', googleJavaFormatJar.path, file.trim()],
+          <String>[javaExe, '-jar', googleJavaFormatJar.path, file.trim()],
         ),
       );
     }
@@ -602,7 +630,7 @@ class JavaFormatChecker extends FormatChecker {
     if (failed.isNotEmpty) {
       final bool plural = failed.length > 1;
       if (fixing) {
-        error('Fixing ${failed.length} Java file${plural ? 's' : ''}'
+        message('Fixing ${failed.length} Java file${plural ? 's' : ''}'
             ' which ${plural ? 'were' : 'was'} formatted incorrectly.');
       } else {
         error('Found ${failed.length} Java file${plural ? 's' : ''}'

engine/src/flutter/ci/test/format_test.dart

@@ -197,10 +197,7 @@ void main() {
     } finally {
       fixture.gitRemove();
     }
-    // TODO(mtolmacs): Fails if Java dependency is unavailable,
-    // https://github.com/flutter/flutter/issues/129221
-    // Java dependency is missing from some Mac bots so only skip those.
-  }, skip: io.Platform.isMacOS);
+  });
 
   test('Can fix Python formatting errors', () {
     final TestFileFixture fixture = TestFileFixture(target.FormatCheck.python);

engine/src/flutter/docs/contributing/Setting-up-the-Engine-development-environment.md

@@ -26,7 +26,6 @@ Make sure you have the following dependencies available:
  * On macOS:
    - Install the latest Xcode.
    - On Apple Silicon arm64 Macs, install the Rosetta translation environment by running `softwareupdate --install-rosetta`.
-   - Install Oracle's Java JDK, version 1.8 or later.
 
 You do not need to install [Dart](https://www.dartlang.org/downloads/linux.html).
 A Dart toolchain is automatically downloaded as part of the "Getting the source"