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[flutter_tools] Ignore widget previews outside lib/ during LSP code generation - #192326

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bkonyi:issue-191755
Sep 9, 2026
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auto-submit[bot] merged 2 commits into
flutter:masterfrom
bkonyi:issue-191755

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@bkonyi bkonyi commented Sep 4, 2026

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Description

Fixes #191755

Previews outside of lib/ (such as at the root of a project or in test/) do not have a package: URI, so FlutterWidgetPreviewDetails.packageName is null.

In #180768, it was established that widget previews must be defined within importable libraries under lib/. Files outside lib/ cannot be safely imported into the widget preview scaffold without breaking asset path mappings or failing to resolve dev_dependencies. While legacy PreviewDetector explicitly ignores libraries where packageName == null, the Dart Analysis Server (LSP) preview detector returns all @Preview annotations across the workspace.

When _buildPreviewsLsp generated the preview list, it force-unwrapped preview.packageName!, crashing with _TypeError: Null check operator used on a null value.

This change filters out previews where packageName == null in PreviewCodeGenerator._buildGeneratedPreviewMethodLsp, ensuring that previews outside lib/ are safely ignored when using LSP preview detection.

Tests

  • Added hermetic unit test ignores previews with null packageName for LSP updates in packages/flutter_tools/test/commands.shard/hermetic/widget_preview/preview_code_generator_test.dart.

…eneration

Previews outside of `lib/` are not valid importable libraries for the widget preview scaffold (consistent with flutter#180768). Filter out previews where `packageName` is null in `_buildGeneratedPreviewMethodLsp` to avoid null check crashes when using the Analysis Server for preview detection.

Fixes flutter#191755
@github-actions github-actions Bot added the tool Affects the "flutter" command-line tool. See also t: labels. label Sep 4, 2026
@bkonyi bkonyi added the CICD Run CI/CD label Sep 5, 2026
@bkonyi
bkonyi requested a review from srawlins September 8, 2026 16:59
@bkonyi
bkonyi marked this pull request as ready for review September 8, 2026 16:59

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Code Review

This pull request filters out previews with a null packageName when generating LSP previews in PreviewCodeGenerator and adds a corresponding test. The review feedback notes that while this prevents a crash, the generated preview scaffold can still fail to compile due to invalid relative imports of files outside the lib/ directory, and suggests also filtering the generated imports and namespaces.

srawlins
srawlins previously approved these changes Sep 8, 2026
… generation

Filters out namespaces for files outside lib/ (those without package: or dart: URIs,
except internal scaffold helpers) in PreviewPrefixedAllocator to avoid emitting invalid
relative imports in the generated preview scaffold.
@bkonyi

bkonyi commented Sep 8, 2026

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Addressed in e6d292d751e. PreviewPrefixedAllocator now filters out non-package/non-SDK imports (retaining only package:, dart:, and internal scaffold helpers) and prevents prefix collisions, with unit test coverage added.

@bkonyi
bkonyi requested a review from srawlins September 8, 2026 20:09
@bkonyi bkonyi added the autosubmit Merge PR when tree becomes green via auto submit App label Sep 9, 2026
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auto-submit Bot added this pull request to the merge queue Sep 9, 2026
Merged via the queue into flutter:master with commit f78893f Sep 9, 2026
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@flutter-dashboard flutter-dashboard Bot removed the autosubmit Merge PR when tree becomes green via auto submit App label Sep 9, 2026
auto-submit Bot pushed a commit to flutter/packages that referenced this pull request Sep 9, 2026
flutter/flutter@b444e78...63b9518

2026-09-09 [email protected] Roll Packages from 9af9c60 to 36e088a (24 revisions) (flutter/flutter#192485)
2026-09-09 [email protected] Re-add Xcode and OpenJDK dependencies to macOS wasm local_engine builders (flutter/flutter#192238)
2026-09-09 [email protected] Roll Dart SDK from 77094991d1c1 to 4be1b711b4ba (5 revisions) (flutter/flutter#192453)
2026-09-09 [email protected] [material] Use super parameters in more places (flutter/flutter#192149)
2026-09-09 [email protected] [cupertino] Use super parameters in more places (flutter/flutter#192148)
2026-09-09 [email protected] [flutter_tools] Gracefully handle EROFS and write-protected file system errors (flutter/flutter#192431)
2026-09-09 [email protected] [tool] Migrate BuildIOSCommand and BuildIOSArchiveCommand to modular dependency injection (flutter/flutter#192250)
2026-09-09 [email protected] Replace more enum instances comparison to use `equality ==` instead of `identical` and update related tests (flutter/flutter#192229)
2026-09-09 [email protected] [web] Support local screenshot and golden testing in felt test (flutter/flutter#191318)
2026-09-09 [email protected] [tool] Migrate DaemonCommand and DebugAdapterCommand to modular dependency injection (flutter/flutter#190793)
2026-09-09 [email protected] [web] Support local golden testing in flutter test (flutter/flutter#191386)
2026-09-09 [email protected] [flutter_tools] Ignore widget previews outside lib/ during LSP code generation (flutter/flutter#192326)
2026-09-09 [email protected] [flutter_tools] Read package_config.json asynchronously in loadPackageConfigWithLogging (flutter/flutter#192443)
2026-09-08 [email protected] Add precacheTestImage to flutter_test and unskip web image tests (flutter/flutter#191435)
2026-09-08 [email protected] et: Fix compile_commands.json post-processing (flutter/flutter#192395)
2026-09-08 [email protected] Refactor createDebuggingOptions and option registrations to OptionDescriptor (flutter/flutter#192307)
2026-09-08 [email protected] [flutter_tools] Fix test separation between `VersionFreshnessValidator` and `FlutterVersion.checkFlutterVersionFreshness` (flutter/flutter#191593)
2026-09-08 [email protected] [tool] Migrate EmulatorsCommand to modular dependency injection (flutter/flutter#190769)
2026-09-08 [email protected] [tool] Migrate Desktop build subcommands and toolchain to modular dependency injection (flutter/flutter#190781)
2026-09-08 [email protected] [tool] Migrate Tooling and Analysis commands to modular dependency injection (flutter/flutter#190788)
2026-09-08 [email protected] Skip KGP version validation for AGP built-in Kotlin (flutter/flutter#192206)

If this roll has caused a breakage, revert this CL and set the roller
to dry run mode using the controls here:
https://autoroll.skia.org/r/flutter-packages
Please CC [email protected],[email protected] on the revert to ensure that a human
is aware of the problem.

To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
victorsanni pushed a commit to victorsanni/packages that referenced this pull request Sep 9, 2026
…r#12814)

flutter/flutter@b444e78...63b9518

2026-09-09 [email protected] Roll Packages from 9af9c60 to 36e088a (24 revisions) (flutter/flutter#192485)
2026-09-09 [email protected] Re-add Xcode and OpenJDK dependencies to macOS wasm local_engine builders (flutter/flutter#192238)
2026-09-09 [email protected] Roll Dart SDK from 77094991d1c1 to 4be1b711b4ba (5 revisions) (flutter/flutter#192453)
2026-09-09 [email protected] [material] Use super parameters in more places (flutter/flutter#192149)
2026-09-09 [email protected] [cupertino] Use super parameters in more places (flutter/flutter#192148)
2026-09-09 [email protected] [flutter_tools] Gracefully handle EROFS and write-protected file system errors (flutter/flutter#192431)
2026-09-09 [email protected] [tool] Migrate BuildIOSCommand and BuildIOSArchiveCommand to modular dependency injection (flutter/flutter#192250)
2026-09-09 [email protected] Replace more enum instances comparison to use `equality ==` instead of `identical` and update related tests (flutter/flutter#192229)
2026-09-09 [email protected] [web] Support local screenshot and golden testing in felt test (flutter/flutter#191318)
2026-09-09 [email protected] [tool] Migrate DaemonCommand and DebugAdapterCommand to modular dependency injection (flutter/flutter#190793)
2026-09-09 [email protected] [web] Support local golden testing in flutter test (flutter/flutter#191386)
2026-09-09 [email protected] [flutter_tools] Ignore widget previews outside lib/ during LSP code generation (flutter/flutter#192326)
2026-09-09 [email protected] [flutter_tools] Read package_config.json asynchronously in loadPackageConfigWithLogging (flutter/flutter#192443)
2026-09-08 [email protected] Add precacheTestImage to flutter_test and unskip web image tests (flutter/flutter#191435)
2026-09-08 [email protected] et: Fix compile_commands.json post-processing (flutter/flutter#192395)
2026-09-08 [email protected] Refactor createDebuggingOptions and option registrations to OptionDescriptor (flutter/flutter#192307)
2026-09-08 [email protected] [flutter_tools] Fix test separation between `VersionFreshnessValidator` and `FlutterVersion.checkFlutterVersionFreshness` (flutter/flutter#191593)
2026-09-08 [email protected] [tool] Migrate EmulatorsCommand to modular dependency injection (flutter/flutter#190769)
2026-09-08 [email protected] [tool] Migrate Desktop build subcommands and toolchain to modular dependency injection (flutter/flutter#190781)
2026-09-08 [email protected] [tool] Migrate Tooling and Analysis commands to modular dependency injection (flutter/flutter#190788)
2026-09-08 [email protected] Skip KGP version validation for AGP built-in Kotlin (flutter/flutter#192206)

If this roll has caused a breakage, revert this CL and set the roller
to dry run mode using the controls here:
https://autoroll.skia.org/r/flutter-packages
Please CC [email protected],[email protected] on the revert to ensure that a human
is aware of the problem.

To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
victorsanni pushed a commit to victorsanni/packages that referenced this pull request Sep 9, 2026
…r#12814)

flutter/flutter@b444e78...63b9518

2026-09-09 [email protected] Roll Packages from 9af9c60 to 36e088a (24 revisions) (flutter/flutter#192485)
2026-09-09 [email protected] Re-add Xcode and OpenJDK dependencies to macOS wasm local_engine builders (flutter/flutter#192238)
2026-09-09 [email protected] Roll Dart SDK from 77094991d1c1 to 4be1b711b4ba (5 revisions) (flutter/flutter#192453)
2026-09-09 [email protected] [material] Use super parameters in more places (flutter/flutter#192149)
2026-09-09 [email protected] [cupertino] Use super parameters in more places (flutter/flutter#192148)
2026-09-09 [email protected] [flutter_tools] Gracefully handle EROFS and write-protected file system errors (flutter/flutter#192431)
2026-09-09 [email protected] [tool] Migrate BuildIOSCommand and BuildIOSArchiveCommand to modular dependency injection (flutter/flutter#192250)
2026-09-09 [email protected] Replace more enum instances comparison to use `equality ==` instead of `identical` and update related tests (flutter/flutter#192229)
2026-09-09 [email protected] [web] Support local screenshot and golden testing in felt test (flutter/flutter#191318)
2026-09-09 [email protected] [tool] Migrate DaemonCommand and DebugAdapterCommand to modular dependency injection (flutter/flutter#190793)
2026-09-09 [email protected] [web] Support local golden testing in flutter test (flutter/flutter#191386)
2026-09-09 [email protected] [flutter_tools] Ignore widget previews outside lib/ during LSP code generation (flutter/flutter#192326)
2026-09-09 [email protected] [flutter_tools] Read package_config.json asynchronously in loadPackageConfigWithLogging (flutter/flutter#192443)
2026-09-08 [email protected] Add precacheTestImage to flutter_test and unskip web image tests (flutter/flutter#191435)
2026-09-08 [email protected] et: Fix compile_commands.json post-processing (flutter/flutter#192395)
2026-09-08 [email protected] Refactor createDebuggingOptions and option registrations to OptionDescriptor (flutter/flutter#192307)
2026-09-08 [email protected] [flutter_tools] Fix test separation between `VersionFreshnessValidator` and `FlutterVersion.checkFlutterVersionFreshness` (flutter/flutter#191593)
2026-09-08 [email protected] [tool] Migrate EmulatorsCommand to modular dependency injection (flutter/flutter#190769)
2026-09-08 [email protected] [tool] Migrate Desktop build subcommands and toolchain to modular dependency injection (flutter/flutter#190781)
2026-09-08 [email protected] [tool] Migrate Tooling and Analysis commands to modular dependency injection (flutter/flutter#190788)
2026-09-08 [email protected] Skip KGP version validation for AGP built-in Kotlin (flutter/flutter#192206)

If this roll has caused a breakage, revert this CL and set the roller
to dry run mode using the controls here:
https://autoroll.skia.org/r/flutter-packages
Please CC [email protected],[email protected] on the revert to ensure that a human
is aware of the problem.

To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
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[tool_crash] _TypeError: (#0 PreviewCodeGenerator._buildPreviewsLsp (package:flutter_tools/src/widget_preview/preview_code_generator.dart:309:58))

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