add --force flag to precache (#31278)

packages/flutter_tools/lib/src/commands/precache.dart

@@ -13,6 +13,8 @@ class PrecacheCommand extends FlutterCommand {
   PrecacheCommand() {
     argParser.addFlag('all-platforms', abbr: 'a', negatable: false,
         help: 'Precache artifacts for all platforms.');
+    argParser.addFlag('force', abbr: 'f', negatable: false,
+        help: 'Force downloading of artifacts.');
     argParser.addFlag('android', negatable: true, defaultsTo: true,
         help: 'Precache artifacts for Android development');
     argParser.addFlag('ios', negatable: true, defaultsTo: true,
@@ -55,10 +57,11 @@ class PrecacheCommand extends FlutterCommand {
         requiredArtifacts.add(artifact);
       }
     }
-    if (cache.isUpToDate()) {
-      printStatus('Already up-to-date.');
-    } else {
+    final bool forceUpdate = argResults['force'];
+    if (forceUpdate || !cache.isUpToDate()) {
       await cache.updateAll(requiredArtifacts);
+    } else {
+      printStatus('Already up-to-date.');
     }
     return null;
   }

packages/flutter_tools/test/commands/precache_test.dart

@@ -63,6 +63,23 @@ void main() {
       Cache: () => cache,
       FlutterVersion: () => flutterVersion,
     });
+
+    testUsingContext('Downloads artifacts when --force is provided', () async {
+      when(cache.isUpToDate()).thenReturn(true);
+      // Release lock between test cases.
+      Cache.releaseLockEarly();
+      final PrecacheCommand command = PrecacheCommand();
+      applyMocksToCommand(command);
+      await createTestCommandRunner(command).run(const <String>['precache', '--force']);
+      expect(artifacts, unorderedEquals(<DevelopmentArtifact>{
+       DevelopmentArtifact.universal,
+       DevelopmentArtifact.iOS,
+       DevelopmentArtifact.android,
+     }));
+    }, overrides: <Type, Generator>{
+      Cache: () => cache,
+      FlutterVersion: () => flutterVersion,
+    });
   });
 }