fix(linter): nursery/noMisusedPromises should emit warnings when a function returns T | Promise<T>

[taga3s]

Summary

• Fixes 💅 noMisusedPromises should emit warning where function returns boolean | Promise<boolean> #8405

This PR enables nursery/noMisusedPromises to emit warnings/errors when a function returns a union type containing a Promise which is used in conditionals.

Test Plan

I added tests to check a function returning boolean | Promise<boolean>.

Docs

[changeset-bot]

🦋 Changeset detected

Latest commit: 68c79cc

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@biomejs/biome	Patch
@biomejs/cli-win32-x64	Patch
@biomejs/cli-win32-arm64	Patch
@biomejs/cli-darwin-x64	Patch
@biomejs/cli-darwin-arm64	Patch
@biomejs/cli-linux-x64	Patch
@biomejs/cli-linux-arm64	Patch
@biomejs/cli-linux-x64-musl	Patch
@biomejs/cli-linux-arm64-musl	Patch
@biomejs/wasm-web	Patch
@biomejs/wasm-bundler	Patch
@biomejs/wasm-nodejs	Patch
@biomejs/backend-jsonrpc	Patch

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[coderabbitai]

Walkthrough

The lint rule noMisusedPromises was changed to always signal for Promise and Promise-like types (including unions such as T | Promise) used in conditionals, removing the prior conditional-state exception. Tests were added/updated to cover a function returning boolean | Promise<boolean> used in if and while statements in both unawaited (invalid) and awaited (valid) forms. No exported/public API signatures were changed.

Suggested labels

A-Type-Inference

Suggested reviewers

• ematipico
• dyc3

Pre-merge checks and finishing touches

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: enabling noMisusedPromises to warn on union types containing Promises used in conditionals.
Description check	✅ Passed	The description clearly relates to the changeset, referencing issue #8405 and explaining the fix for detecting union types in conditionals.
Linked Issues check	✅ Passed	The PR fully addresses issue #8405 by modifying the signal logic to detect Promise-like types regardless of conditional state, and adds test coverage for boolean | Promise scenarios.
Out of Scope Changes check	✅ Passed	All changes directly support the stated objective of fixing noMisusedPromises for union types; no out-of-scope modifications detected.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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📒 Files selected for processing (1)

• .changeset/fuzzy-crabs-smash.md

🚧 Files skipped from review as they are similar to previous changes (1)

• .changeset/fuzzy-crabs-smash.md

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• GitHub Check: Test (depot-windows-2022-16)
• GitHub Check: Test (depot-ubuntu-24.04-arm-16)
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• GitHub Check: Validate rules documentation

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[codspeed-hq]

CodSpeed Performance Report

Merging #8495 will not alter performance

_{Comparing taga3s:fix-no-misused-promises-when-returns-union (68c79cc) with main (6b09620)¹}

Summary

✅ 58 untouched
⏩ 95 skipped²

Footnotes

1. No successful run was found on main (90121d1) during the generation of this report, so 6b09620 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 95 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[coderabbitai]

Actionable comments posted: 1

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⛔ Files ignored due to path filters (2)

• crates/biome_js_analyze/tests/specs/nursery/noMisusedPromises/checksConditionalsInvalid.ts.snap is excluded by !**/*.snap and included by **
• crates/biome_js_analyze/tests/specs/nursery/noMisusedPromises/checksConditionalsValid.ts.snap is excluded by !**/*.snap and included by **

📒 Files selected for processing (4)

• .changeset/fuzzy-crabs-smash.md (1 hunks)
• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs (1 hunks)
• crates/biome_js_analyze/tests/specs/nursery/noMisusedPromises/checksConditionalsInvalid.ts (1 hunks)
• crates/biome_js_analyze/tests/specs/nursery/noMisusedPromises/checksConditionalsValid.ts (1 hunks)

🧰 Additional context used

📓 Path-based instructions (2)

.changeset/*.md

📄 CodeRabbit inference engine (CONTRIBUTING.md)

Write changesets that are concise (1-3 sentences), user-focused, use past tense for actions taken and present tense for Biome behavior, include code examples for rules, and end sentences with periods

Files:

• .changeset/fuzzy-crabs-smash.md

crates/**/*.rs

📄 CodeRabbit inference engine (CONTRIBUTING.md)

Update inline rustdoc documentation for rules, assists, and their options when adding new features or changing existing features in Rust crates

Files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

🧠 Learnings (14)

📓 Common learnings

Learnt from: CR
Repo: biomejs/biome PR: 0
File: CONTRIBUTING.md:0-0
Timestamp: 2025-12-12T10:11:05.549Z
Learning: Send PRs with bug fixes or documentation fixes to the `main` maintenance branch; send PRs with new nursery rules to `main`; send PRs promoting rules from nursery or implementing user-facing features to the `next` branch

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Commit rule changes with message format: `feat(biome_<crate>): <ruleName>` to follow Biome's conventional commit style

Applied to files:

• .changeset/fuzzy-crabs-smash.md

📚 Learning: 2025-12-12T10:11:05.549Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: CONTRIBUTING.md:0-0
Timestamp: 2025-12-12T10:11:05.549Z
Learning: Create a changeset for user-facing bug fixes and features using `just new-changeset`, selecting appropriate packages and change type (`major`, `minor`, or `patch`)

Applied to files:

• .changeset/fuzzy-crabs-smash.md

📚 Learning: 2025-12-12T10:11:05.549Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: CONTRIBUTING.md:0-0
Timestamp: 2025-12-12T10:11:05.549Z
Learning: Applies to .changeset/*.md : Write changesets that are concise (1-3 sentences), user-focused, use past tense for actions taken and present tense for Biome behavior, include code examples for rules, and end sentences with periods

Applied to files:

• .changeset/fuzzy-crabs-smash.md

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Applies to crates/biome_analyze/**/*analyze/src/lint/**/*.rs : Avoid using `unwrap()` or `expect()` on `Result` and `Option` types; instead use helper functions like `map`, `filter`, `and_then` to maintain code clarity and avoid panics

Applied to files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Applies to crates/biome_analyze/**/*analyze/src/lint/**/*.rs : Check if a variable is global before banning it to avoid false positives when the variable is redeclared in local scope; use the semantic model to verify global scope

Applied to files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Applies to crates/biome_analyze/**/*analyze/src/lint/**/*.rs : Lint rules must be implemented using the `Rule` trait with type parameters: `Query` (node type to analyze), `State` (information for signals), `Signals` (return type from run function), and `Options` (rule configuration)

Applied to files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Applies to crates/biome_analyze/**/*analyze/src/lint/**/*.rs : Use the `noMisleading` prefix for rules that report valid but potentially misleading code (e.g., `noMisleadingCharacterClass`)

Applied to files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Applies to crates/biome_analyze/**/*analyze/src/lint/**/*.rs : Use the `noUseless` prefix for rules that report unnecessary code that could be removed or simplified (e.g., `noUselessConstructor`)

Applied to files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Applies to crates/biome_analyze/**/*analyze/src/lint/**/*.rs : Use the `noUnsafe` prefix for rules that report code leading to runtime failures (e.g., `noUnsafeOptionalChaining`)

Applied to files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Applies to crates/biome_analyze/**/*analyze/src/lint/**/*.rs : Use the `noRedundant` prefix for rules that report redundant code (e.g., `noRedundantUseStrict`)

Applied to files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Applies to crates/biome_analyze/**/*analyze/src/lint/**/*.rs : Use the `noInvalid` prefix for rules that report runtime errors from mistyping (e.g., `noInvalidConstructorSuper`)

Applied to files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Applies to crates/biome_analyze/**/*analyze/src/lint/**/*.rs : When navigating CST nodes that return `Result`, use the try operator `?` to convert to `Option`, or use `let else` pattern for `Vec` return types in rule run functions

Applied to files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

📚 Learning: 2025-11-27T23:04:02.022Z

Learnt from: CR
Repo: biomejs/biome PR: 0
File: crates/biome_analyze/CONTRIBUTING.md:0-0
Timestamp: 2025-11-27T23:04:02.022Z
Learning: Applies to crates/biome_analyze/**/*analyze/src/lint/**/*.rs : Use the `noConstant` prefix for rules that report computations always evaluated to the same value (e.g., `noConstantMathMinMaxClamp`)

Applied to files:

• crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (5)

• GitHub Check: Test Node.js API
• GitHub Check: Bench (biome_js_analyze)
• GitHub Check: Bench (biome_js_formatter)
• GitHub Check: Bench (biome_js_parser)
• GitHub Check: autofix

🔇 Additional comments (3)

crates/biome_js_analyze/src/lint/nursery/no_misused_promises.rs (1)

238-238: Logic simplification looks correct.

The change now consistently flags both direct Promises and union types containing Promises, matching the behaviour in find_misused_promise_returning_callback (lines 252-253). This correctly addresses the issue where boolean | Promise<boolean> wasn't flagged in conditionals.

crates/biome_js_analyze/tests/specs/nursery/noMisusedPromises/checksConditionalsInvalid.ts (1)

15-25: Excellent test coverage for the union type scenario.

The test cases properly cover the reported issue: a function returning boolean | Promise<boolean> used in conditionals without await.

crates/biome_js_analyze/tests/specs/nursery/noMisusedPromises/checksConditionalsValid.ts (1)

21-31: Well done on the valid test cases.

Properly demonstrates that awaiting the union type result in conditionals is the correct pattern and shouldn't trigger the rule.