Dont update last compiled time when compilation is rejected (#41424)

packages/flutter_tools/lib/src/devfs.dart

@@ -465,7 +465,6 @@ class DevFS {
       generator.reset();
     }
     printTrace('Compiling dart to kernel with ${invalidatedFiles.length} updated files');
-    lastCompiled = DateTime.now();
     final CompilerOutput compilerOutput = await generator.recompile(
       mainPath,
       invalidatedFiles,
@@ -475,6 +474,8 @@ class DevFS {
     if (compilerOutput == null || compilerOutput.errorCount > 0) {
       return UpdateFSReport(success: false);
     }
+    // Only update the last compiled time if we successfully compiled.
+    lastCompiled = DateTime.now();
     // list of sources that needs to be monitored are in [compilerOutput.sources]
     sources = compilerOutput.sources;
     //

packages/flutter_tools/test/general.shard/devfs_test.dart

@@ -178,6 +178,7 @@ void main() {
     testUsingContext('reports unsuccessful compile when errors are returned', () async {
       devFS = DevFS(vmService, 'test', tempDir);
       await devFS.create();
+      final DateTime previousCompile = devFS.lastCompiled;
 
       final RealMockResidentCompiler residentCompiler = RealMockResidentCompiler();
       when(residentCompiler.recompile(
@@ -197,6 +198,7 @@ void main() {
       );
 
       expect(report.success, false);
+      expect(devFS.lastCompiled, previousCompile);
     }, overrides: <Type, Generator>{
       FileSystem: () => fs,
     });