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Re-add the ability to return null in ListView.builder#108706

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rrousselGit:null-item-builder
Sep 20, 2022
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Re-add the ability to return null in ListView.builder#108706
auto-submit[bot] merged 16 commits into
flutter:masterfrom
rrousselGit:null-item-builder

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@rrousselGit

@rrousselGit rrousselGit commented Jul 31, 2022

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Fixes a possible regression during NNBD migration that removed the ability to return null in ListView.builder's itemBuilder

fixes #108705

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  • I read the Contributor Guide and followed the process outlined there for submitting PRs.
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  • 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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@flutter-dashboard flutter-dashboard Bot added f: scrolling Viewports, list views, slivers, etc. framework flutter/packages/flutter repository. See also f: labels. labels Jul 31, 2022
@goderbauer

goderbauer commented Aug 2, 2022

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(from triage): Looks like some tests are failing on this, could you take a look and fix those up?

@goderbauer
goderbauer requested a review from Piinks August 2, 2022 22:15
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Comment thread packages/flutter/lib/src/widgets/scroll_view.dart Outdated
@rrousselGit

rrousselGit commented Aug 8, 2022

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(from triage): Looks like some tests are failing on this, could you take a look and fix those up?

I'd happily try to fix the CI, but the error messages are unreadable

Example:

��������������������������������������������������������

Any thought on how I could get a readable explanation of the problem? Otherwise I'll have a hard time fixing the issue.

@goderbauer

goderbauer commented Aug 8, 2022

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The failure appears pretty clearly in the log [1]:

03:48 +2804 ~52: /tmp/flutter sdk/packages/flutter/test/widgets/scroll_view_test.dart: ListView.separated supports null items in itemBuilder                                                           
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following TestFailure was thrown running a test:
Expected: exactly 4 matching nodes in the widget tree
  Actual: _TextFinder:<5 widgets with text "separator" (ignoring offstage widgets):
Text("separator", dependencies: [DefaultSelectionStyle, DefaultTextStyle, MediaQuery]),
Text("separator", dependencies: [DefaultSelectionStyle, DefaultTextStyle, MediaQuery]),
Text("separator", dependencies: [DefaultSelectionStyle, DefaultTextStyle, MediaQuery]), ...>
   Which: is too many
When the exception was thrown, this was the stack:
#4      main.<anonymous closure> (file:///tmp/flutter%20sdk/packages/flutter/test/widgets/scroll_view_test.dart:179:5)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from package:stack_trace)
This was caught by the test expectation on the following line:
  file:///tmp/flutter%20sdk/packages/flutter/test/widgets/scroll_view_test.dart line 179
The test description was:
  ListView.separated supports null items in itemBuilder
════════════════════════════════════════════════════════════════════════════════════════════════════

[1] https://cirrus-ci.com/task/6670346764943360?logs=main#L801

@rrousselGit

rrousselGit commented Aug 9, 2022

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Thanks! Weird that Github action doesn't render them clearly. I'll look into it

@goderbauer
goderbauer requested a review from Piinks August 16, 2022 22:13
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Thanks for the updates. So we have updated PageView, ListView, and GridView here, and it looks like AnimatedList, ReorderableList are confirmed not relevant.
It also looks like CupertinoTabScaffold specifies in the docs that tabBuilder cannot be null.

For the three cases that are changing to NullableIndexedWidgetBuilder can you add a templated doc that clarifies the behavior when using null to indicate the end of the list? The max scroll extent will not be accurate unless you are at the end of the list for example. This has caused confusion for a lot of folks in the past, so reintroducing this gives us a better chance to document it. :)

@rrousselGit

rrousselGit commented Aug 24, 2022

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Sorry, I missed your message!

I'll update the docs after the Flutter Vikings (1st of September).

@goderbauer

goderbauer commented Sep 13, 2022

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(triage): @rrousselGit Do you have another chance to look at this now that Vikings is over?

@rrousselGit

rrousselGit commented Sep 14, 2022

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Oops, sorry for the delay. Done

Piinks
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This LGTM with nits, but it looks like CI is unhappy. Can you rebase with master to see if it resolves the failures?

Comment thread packages/flutter/lib/src/widgets/scroll_view.dart Outdated
Comment thread packages/flutter/lib/src/widgets/scroll_view.dart Outdated
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Thanks for the updates! The docs test looks unhappy, but I've noted where the issues are below.

Comment thread packages/flutter/lib/src/widgets/page_view.dart Outdated
Comment thread packages/flutter/lib/src/widgets/scroll_view.dart
/// [ListView] itself is created, it is more efficient to use the [ListView]
/// constructor. Even more efficient, however, is to create the instances on
/// demand using this constructor's `itemBuilder` callback.
///

@Piinks Piinks Sep 16, 2022

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This needs an /// {@endtemplate}

@rrousselGit rrousselGit Sep 17, 2022

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There is one, it is in the paragraph above

This paragraph isn't part of the @template

Comment thread packages/flutter/lib/src/widgets/scroll_view.dart Outdated
@rrousselGit

rrousselGit commented Sep 17, 2022

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Oh, my bad. Let me fix that

@Piinks

Piinks commented Sep 19, 2022

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Oh, my bad. Let me fix that

No worries, appeasing the CI gods can feel a bit tedious at times. Thanks for sticking with it!

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Flutter_LGTM

@Piinks Piinks added the autosubmit Merge PR when tree becomes green via auto submit App label Sep 19, 2022
@auto-submit auto-submit Bot removed the autosubmit Merge PR when tree becomes green via auto submit App label Sep 19, 2022
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auto-submit Bot commented Sep 19, 2022

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auto label is removed for flutter/flutter, pr: 108706, due to - Please get at least one approved review if you are already a member or two member reviews if you are not a member before re-applying this label. Reviewers: If you left a comment approving, please use the "approve" review action instead.

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auto label is removed for flutter/flutter, pr: 108706, due to Validations Fail.

@Piinks

Piinks commented Sep 19, 2022

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Ah we need a second reviewer, I'll seek one.

justinmc
justinmc approved these changes Sep 19, 2022
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LGTM 👍

Comment thread packages/flutter/lib/src/widgets/scroll_view.dart
@Piinks Piinks added autosubmit Merge PR when tree becomes green via auto submit App and removed autosubmit Merge PR when tree becomes green via auto submit App labels Sep 20, 2022
@Piinks Piinks added the autosubmit Merge PR when tree becomes green via auto submit App label Sep 20, 2022
@auto-submit
auto-submit Bot merged commit 6f3168c into flutter:master Sep 20, 2022
@rrousselGit
rrousselGit deleted the null-item-builder branch September 20, 2022 19:03
This was referenced Sep 21, 2022
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engine-flutter-autoroll added a commit to engine-flutter-autoroll/packages that referenced this pull request Sep 21, 2022
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6f3168c Re-add the ability to return null in ListView.builder (flutte…
b0c969c 
…r/flutter#108706)
engine-flutter-autoroll added a commit to engine-flutter-autoroll/plugins that referenced this pull request Sep 21, 2022
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6f3168c Re-add the ability to return null in ListView.builder (flutte…
63e0370 
…r/flutter#108706)
galiperkin
galiperkin reviewed Jan 30, 2023
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Changes are reviewed. LGTM.

@HansMuller HansMuller mentioned this pull request Feb 28, 2024
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@laiiihz laiiihz mentioned this pull request Nov 13, 2024
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Regression: ListView.builder's itemBuilder can no-longer return null since NNBD migration

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@rrousselGit @goderbauer @Piinks @justinmc @galiperkin