Audit `covariant` usage in tool by jmagman · Pull Request #114112 · flutter/flutter

jmagman · 2022-10-26T22:03:04Z

Remove covariant where possible to avoid subtle null safety issue. Where it's still useful, remove from base class and push covariant into overrides to by-default enforce nullability where covariant isn't needed.

See https://dart.dev/guides/language/sound-problems#the-covariant-keyword about how this suppresses the analyzer.

Some (rarely used) coding patterns rely on tightening a type by overriding a parameter’s type with a subtype, which is invalid. In this case, you can use the covariant keyword to tell the analyzer that you are doing this intentionally. This removes the static error and instead checks for an invalid argument type at runtime.

This will need a g3fix.

Note I left the covariant in startApp. That one is really a mess since most subclasses do expect it to be non-null, but it is legitimately called as null in the web case. I guess we can leave that one for now until it causes issues...

flutter/packages/flutter_tools/lib/src/isolated/resident_web_runner.dart

Lines 242 to 245 in 156c313

    
           if (package == null) { 
        
             _logger!.printStatus('This application is not configured to build on the web.'); 
        
             _logger!.printStatus('To add web support to a project, run `flutter create .`.'); 
        
           }

Fixes #114090

Pre-launch Checklist

I read the Contributor Guide and followed the process outlined there for submitting PRs.
I read the Tree Hygiene wiki page, which explains my responsibilities.
I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
I signed the CLA.
I listed at least one issue that this PR fixes in the description above.
I updated/added relevant documentation (doc comments with ///).
I added new tests to check the change I am making, or this PR is test-exempt.
All existing and new tests are passing.

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jmagman · 2022-10-26T22:04:12Z

packages/flutter_tools/lib/src/desktop_device.dart


  /// Builds the current project for this device, with the given options.
-  Future<void> buildForDevice(
-    ApplicationPackage package, {


package wasn't used in any of the subclass implementation, remove.

jmagman · 2022-10-26T22:06:14Z

packages/flutter_tools/lib/src/ios/simulators.dart

  @override
  Future<bool> stopApp(
-    ApplicationPackage app, {
+    ApplicationPackage? app, {


This is where the nullability mismatch caused the runtime test failure seen during the roll

Since covariant has been removed from the base class signature, there was correctly an error when this wasn't nullable.

jmagman · 2022-10-26T23:16:30Z

packages/flutter_tools/lib/src/resident_runner.dart

      );
    }

-    if (package == null) {


Rearranged this check to be above the 'Launching ${package!.displayName} ' call, which would crash.

christopherfujino · 2022-10-29T00:12:26Z

packages/flutter_tools/lib/src/android/android_device.dart

  @override
  Future<bool> isAppInstalled(
-    AndroidApk app, {
+    ApplicationPackage app, {


so for this call, will we just be more permissive and allow any ApplicationPackage?

I wonder if the right solution to this is not to make Device:

abstract class Device<A extends ApplicationPackage> { isAppInstalled(A app, ...) {} }

That would be a much better solution, but it also means every single usage of the base class Device becomes Device<ApplicationPackage> if we can't derive the implemented type, and we have hundreds of them.

info: Specify type annotations. (always_specify_types)

I gave up with about 400 more warnings to go:
e780f1d

What do you want me to do with this PR?

let me make one more pass, we can land as is

christopherfujino · 2022-10-29T00:13:44Z

packages/flutter_tools/lib/src/android/android_device.dart

  @override
  Future<bool> uninstallApp(
-    AndroidApk app, {
+    ApplicationPackage app, {


why not covariant AndroidApk here?

Because covariant AndroidApk would turns off the static analysis for this type, so if the base class switched to ApplicationPackage? say, the analyzer wouldn't complain and we'd be back where we started.

yup, I forgot

christopherfujino · 2022-10-29T00:14:35Z

packages/flutter_tools/lib/src/android/android_device.dart

  @override
  Future<LaunchResult> startApp(
-    AndroidApk package, {
+    AndroidApk? package, {


Why allow null for Android app?

It should be nullable because the base class is nullable due to web. That's the bug this is fixing--covariant was hiding that null could be passed in, which in some cases caused crashes.

yup, that was a brain fart on my part

christopherfujino · 2022-10-29T00:15:53Z

packages/flutter_tools/lib/src/android/android_device.dart

  @override
  Future<bool> stopApp(
-    AndroidApk? app, {
+    ApplicationPackage? app, {


why not covariant AndroidApk?

christopherfujino

LGTM

jmagman · 2022-11-09T21:10:59Z

Despite the passing Google Testing, this had a FRoB test failure and needs a g3fix before it can merge.

jmagman · 2022-12-12T22:22:30Z

Going to reopen this and hopefully get new google testing failures.

Audit covariant usage in tool

cbf4ce3

jmagman added tool Affects the "flutter" command-line tool. See also t: labels. c: tech-debt Technical debt, code quality, testing, etc. labels Oct 26, 2022

jmagman self-assigned this Oct 26, 2022

flutter-dashboard bot added the platform-ios iOS applications specifically label Oct 26, 2022

jmagman commented Oct 26, 2022

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jmagman changed the title ~~Audit covariant usage in tool~~ Audit covariant usage in tool Oct 26, 2022

tests

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jmagman commented Oct 26, 2022

View reviewed changes

delete NullFakeApplicationPackageFactory

38f180a

jmagman mentioned this pull request Oct 27, 2022

Terminate simulator app on "q" #114114

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jmagman requested a review from christopherfujino October 28, 2022 17:44

christopherfujino reviewed Oct 29, 2022

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christopherfujino approved these changes Nov 8, 2022

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christopherfujino mentioned this pull request Nov 8, 2022

Google testing being scheduled but never completes #114858

Closed

jmagman closed this Dec 12, 2022

jmagman deleted the covariant branch December 12, 2022 22:22

jmagman mentioned this pull request Dec 12, 2022

Audit covariant usage in tool #116930

Merged

8 tasks

	if (package == null) {
	_logger!.printStatus('This application is not configured to build on the web.');
	_logger!.printStatus('To add web support to a project, run `flutter create .`.');
	}

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jmagman commented Nov 9, 2022

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