[SuperEditor][Mobile] Fix downstream image caret position (Resolves #1959)

[angelosilvestre]

[SuperEditor][Mobile] Fix downstream image caret position. Resolves #1959

Tapping close to the trailing edge of an image places the selection correctly, but the caret isn't displayed. We had the same issue in the past on desktop. It was fixed by #1820, but mobile doesn't use the same caret layer that desktop uses, so the issue is still present on mobile.

The root cause is the same of the desktop issue:

The downstream caret is positioned at (right, 0), so when the image takes all the available screen width (like in the demo app), the caret is positioned off-screen. Block level elements that have padding don't have this issue, because there is room to render the caret.

The same solution was applied:

This PR changes the caret overlay to check whether the caret rect is placed outside of its bounds at the right side. If it is, the caret position is adjusted.

The golden tests for Android are still failing due to this exception:

══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following assertion was thrown running a test:
'package:flutter_test/src/_matchers_io.dart': Failed assertion: line 29 pos 10:
'!renderObject.debugNeedsPaint': is not true.

When the exception was thrown, this was the stack:
#2      captureImage (package:flutter_test/src/_matchers_io.dart:29:10)
#3      MatchesGoldenFile.matchAsync (package:flutter_test/src/_matchers_io.dart:96:21)
#4      _expect (package:matcher/src/expect/expect.dart:109:26)
#5      expectLater (package:matcher/src/expect/expect.dart:73:5)
#6      expectLater (package:flutter_test/src/widget_tester.dart:511:25)
#7      compareWithGolden (package:golden_toolkit/src/testing_tools.dart:296:9)

It seems to be caused by the Follower used by the Android collapsed handle.

[angelosilvestre]

@matthew-carroll Can you do a first pass review?

I still don't know what to do with this assertion failure, but it should impact the fix.

[angelosilvestre]

@matthew-carroll We had the golden test issue on the past on linux and worked around that with the following code:

 @override
  void markNeedsPaint() {
    super.markNeedsPaint();

    if (kDebugMode &&
        !kIsWeb &&
        Platform.isLinux &&
        Platform.environment.containsKey('FLUTTER_TEST') &&
        !WidgetsBinding.instance.hasScheduledFrame) {
      // We are running on a linux test and we don't have a scheduled frame.
      //
      // We ran into an issue in some golden tests, on linux only, where `debugNeedsPaint`
      // is `true` after the build/layout/phase pipeline. This causes the tests to fail,
      // because trying to capture the image of a `RenderObject` throws an assertion failure
      // if `debugNeedsPaint` is `true`. To avoid that, immediately schedule a new frame,
      // so Flutter pipeline runs again before we try to capture the image.
      WidgetsBinding.instance.scheduleFrame();
    }
  }

Should we also check for Android?

[matthew-carroll]

@angelosilvestre I think we mentioned it on our call, but you can go ahead and let that particular check run for all platforms.

[matthew-carroll]

CC @BazinC

[angelosilvestre]

@matthew-carroll I'm getting a failure on the new goldens on CI only that seems related to some antialiasing on the drag handle.

Test image:

Master image:

Isolate diff:

Any ideas?

[matthew-carroll]

@angelosilvestre can you just regenerate that golden?

[angelosilvestre]

@matthew-carroll Locally, the regenerated golden is identical to the previous one...

[matthew-carroll]

@angelosilvestre if your local Flutter version is identical to the CI Flutter version, then I'm not sure why we're seeing different results. If that's truly the case, then consider using the tooling that we created, which allows a certain number of pixels to be different before failing the test.

[angelosilvestre]

After using our tooling that tolerates small differences, I got back to the infamous debugNeedsPaint assertion failure.

[matthew-carroll]

@angelosilvestre are the goldens the only remaining problem? If so, let's file an issue to look into it and get this fix merged.

[angelosilvestre]

@matthew-carroll Yes, the only problem is the failing goldens on Android. I modified these tests to be skipped so we can try to find out the reason.

[matthew-carroll]

LGTM

[matthew-carroll]

@angelosilvestre please be sure to file an issue, if you haven't already