feat(eslint-plugin): [no-unnecessary-condition] check type predicates based on assignability

[kirkwaiblinger]

PR Checklist

• [x] Addresses an existing open issue: fixes #11798
• [x] That issue was marked as accepting prs
• [x] Steps in Contributing were taken

Overview

TODO

[typescript-eslint[bot]]

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View your CI Pipeline Execution ↗ for commit c17df5c62ccffe425ed3fefc17fffec2c72597d0

Command	Status	Duration	Result
nx run-many -t lint	❌ Failed	3m 12s	View ↗
nx test eslint-plugin --coverage=false	✅ Succeeded	5m 13s	View ↗
nx run-many -t typecheck	✅ Succeeded	2m 10s	View ↗
nx test eslint-plugin-internal --coverage=false	✅ Succeeded	10s	View ↗
nx test typescript-estree --coverage=false	✅ Succeeded	2s	View ↗
nx run types:build	✅ Succeeded	2s	View ↗
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☁️ Nx Cloud last updated this comment at 2025-11-26 10:40:13 UTC

[codecov[bot]]

Codecov Report

:x: Patch coverage is 89.13043% with 5 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 90.49%. Comparing base (17601fc) to head (c17df5c).

Files with missing lines	Patch %	Lines
...slint-plugin/src/rules/no-unnecessary-condition.ts	85.29%	4 Missing and 1 partial :warning:

:x: Your patch check has failed because the patch coverage (89.13%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11799      +/-   ##
==========================================
- Coverage   90.49%   90.49%   -0.01%     
==========================================
  Files         522      523       +1     
  Lines       53357    53385      +28     
  Branches     8909     8919      +10     
==========================================
+ Hits        48284    48309      +25     
- Misses       5057     5059       +2     
- Partials       16       17       +1     

Flag	Coverage Δ
unittest	90.49% <89.13%> (-0.01%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
.../eslint-plugin/src/rules/class-methods-use-this.ts	100.00% <100.00%> (ø)
...plugin/src/rules/no-unnecessary-type-parameters.ts	97.08% <ø> (ø)
...slint-plugin/src/rules/no-unsafe-type-assertion.ts	100.00% <100.00%> (ø)
packages/eslint-plugin/src/util/isObjectType.ts	100.00% <100.00%> (ø)
...ckages/rule-tester/src/utils/flat-config-schema.ts	40.65% <ø> (ø)
...slint-plugin/src/rules/no-unnecessary-condition.ts	98.90% <85.29%> (-0.67%)	:arrow_down:

... and 1 file with indirect coverage changes

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