fix(linter): detect floating promises through cross-module generic wrappers by bmish · Pull Request #9835 · biomejs/biome

bmish · 2026-04-06T20:03:45Z

Summary

noFloatingPromises missed unhandled promises when an async function was wrapped by a generic identity function defined in another module, a common pattern for tracing decorators, instrumentation wrappers, and memoization helpers:

// trace.ts
export function trace<F extends (...args: any) => any>(fn: F): F { return fn; }

// wrapper.ts
import { trace } from "./trace";
async function _doWork(id: string): Promise<void> { /* ... */ }
export const doWork = trace(_doWork);
export const maybeDoWork: typeof doWork | undefined = doWork;

// index.ts
import { doWork, maybeDoWork } from "./wrapper";
async function main() {
  doWork("abc"); // ← floating promise, was not detected
  maybeDoWork?.("xyz"); // ← also not detected (union-typed callee)
}

The root cause was two gaps in type flattening (expressions.rs):

Unhandled TypeofExpression callees. resolve_callee_to_function could resolve Function, InstanceOf, Interface, and Object callees, but not TypeofExpression. When an imported binding's type is an unflattened call expression (e.g. typeof trace(asyncFn)), the callee couldn't be resolved to its underlying function type. Fixed by adding a TypeofExpression arm that eagerly flattens the expression.
TypeofExpression skipped inside union-typed callees. flattened_call explicitly skipped TypeofExpression variants when iterating through a union callee (e.g. typeof doWork | undefined from an optional call maybeDoWork?.(...)). This prevented detection even after fix 1. Fixed by removing the skip so these variants fall through to resolve_callee_to_function.

Known limitations

Nested/chained generic wrappers (memoize(trace(asyncFn))) across modules are still not detected. The inner TypeofCallExpression argument isn't flattened during generic inference in flattened_function_call, so the composed result doesn't resolve to a function type. This is a pre-existing limitation and could be addressed separately.

Related issues

Partially addresses #7332

Test plan

invalidGenericWrapper/ — three-file test (index -> wrapper -> trace) with generic trace<F>(fn: F): F, verifies diagnostics for Promise<void> and Promise<string> return types, plus an optional call through a union-typed binding (maybeDoWork?.("xyz")).
validGenericWrapper/ — same topology, verifies no false positives when calls are properly handled (await, void, .catch()), and that sync functions through the wrapper are not flagged.
invalidTwoHopImport/ — two-hop re-export without generics (base -> reexport -> index).
20_invalid.ts — single-file generic wrapper (same-module baseline).
All 46 noFloatingPromises tests, 2326 biome_js_analyze spec tests, and 46 biome_module_graph tests pass. Clippy clean.

This PR was written primarily with AI assistance (Claude).

…appers Two issues prevented `noFloatingPromises` from detecting unhandled promises when async functions were wrapped by cross-module generic identity functions (e.g. `export const fn = trace(asyncFn)` where `trace<F>(fn: F): F`). 1. When types are copied from a module's local (Thin) store to the project-wide (Full) resolver, inner `TypeReference::Resolved` fields inside compound types like `TypeofCallExpression` retained stale Thin-level IDs. Add a remapping pass in `ModuleResolver::resolve_all` that rewrites these inner references to Full-level IDs. 2. `resolve_callee_to_function` did not handle `TypeofExpression` callees, so imported bindings whose types were unflattened call expressions (e.g. `typeof trace(asyncFn)`) could not be resolved to their underlying function type. Add a `TypeofExpression` arm that eagerly flattens the expression. Made-with: Cursor

changeset-bot · 2026-04-06T20:03:52Z

🦋 Changeset detected

Latest commit: 1335923

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 · 2026-04-06T20:25:40Z

Walkthrough

Updates enable the noFloatingPromises linter rule to detect floating promises when promise-returning functions are wrapped by cross-module generic wrappers. New TypeScript test fixtures cover valid and invalid generic-wrapper and two-hop import scenarios. Implementation changes traverse TypeofExpression during callee-to-function resolution and add a post-processing remap of module-level TypeReference::Resolved entries to full resolved type IDs during module resolution.

Suggested reviewers

dyc3
ematipico

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarises the core change: detecting floating promises through cross-module generic wrappers, which is the primary objective of the PR.
Description check	✅ Passed	The PR description clearly explains the bug (floating promises missed through cross-module generic wrappers), provides concrete examples, identifies root causes, details the fixes implemented, and documents test coverage.

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In @.changeset/fix-no-floating-promises-generic-wrappers.md:
- Line 5: Update the changeset description so it begins with the repository
bug-fix prefix; replace the existing first sentence ("The `noFloatingPromises`
rule now detects floating promises through cross-module generic wrapper
functions...") with a line that starts with the bug-fix format, e.g. "Fixed
[`#7332`](https://github.com/biomejs/biome/issues/7332): The `noFloatingPromises`
rule now detects floating promises through cross-module generic wrapper
functions..." to match the required `.changeset/*.md` convention and ensure
release notes parse correctly; edit the file named
.changeset/fix-no-floating-promises-generic-wrappers.md and update the existing
description line accordingly.

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📥 Commits

Reviewing files that changed from the base of the PR and between 3884c04 and de7645e.

⛔ Files ignored due to path filters (18)

crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/20_invalid.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidGenericWrapper/index.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidGenericWrapper/trace.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidGenericWrapper/wrapper.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidTwoHopImport/base.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidTwoHopImport/index.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidTwoHopImport/reexport.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/validGenericWrapper/index.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/validGenericWrapper/trace.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/validGenericWrapper/wrapper.ts.snap is excluded by !**/*.snap and included by **
crates/biome_module_graph/tests/snapshots/test_resolve_generic_mapped_value.snap is excluded by !**/*.snap and included by **
crates/biome_module_graph/tests/snapshots/test_resolve_generic_return_value.snap is excluded by !**/*.snap and included by **
crates/biome_module_graph/tests/snapshots/test_resolve_generic_return_value_with_multiple_modules.snap is excluded by !**/*.snap and included by **
crates/biome_module_graph/tests/snapshots/test_resolve_nested_function_call_with_namespace_in_return_type.snap is excluded by !**/*.snap and included by **
crates/biome_module_graph/tests/snapshots/test_resolve_type_of_destructured_field_of_intersection_of_interfaces.snap is excluded by !**/*.snap and included by **
crates/biome_module_graph/tests/snapshots/test_resolve_type_of_intersection_of_interfaces.snap is excluded by !**/*.snap and included by **
crates/biome_module_graph/tests/snapshots/test_widening_via_assignment.snap is excluded by !**/*.snap and included by **
crates/biome_module_graph/tests/snapshots/test_widening_via_assignment_multiple_values.snap is excluded by !**/*.snap and included by **

📒 Files selected for processing (13)

.changeset/fix-no-floating-promises-generic-wrappers.md
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/20_invalid.ts
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidGenericWrapper/index.ts
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidGenericWrapper/trace.ts
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidGenericWrapper/wrapper.ts
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidTwoHopImport/base.ts
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidTwoHopImport/index.ts
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/invalidTwoHopImport/reexport.ts
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/validGenericWrapper/index.ts
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/validGenericWrapper/trace.ts
crates/biome_js_analyze/tests/specs/nursery/noFloatingPromises/validGenericWrapper/wrapper.ts
crates/biome_js_type_info/src/flattening/expressions.rs
crates/biome_module_graph/src/js_module_info/module_resolver.rs

… generic wrappers TypeofExpression callees inside union types (e.g. optional calls via `?.`) were being skipped in `flattened_call`, preventing detection. Remove the skip so they fall through to `resolve_callee_to_function` which already handles TypeofExpression flattening. Made-with: Cursor

ematipico · 2026-04-07T03:24:27Z

These stale references caused lookups to resolve to the wrong type (e.g. ImportNamespace instead of the actual function binding).

Can you actually explain it with actual code? Are there tests you can point to?

codspeed-hq · 2026-04-07T03:28:53Z

Merging this PR will not alter performance

✅ 58 untouched benchmarks
⏩ 196 skipped benchmarks¹

_{Comparing bmish:fix/no-floating-promises-cross-module-generic-wrappers (1335923) with main (82b9c4a)}

196 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. ↩

bmish · 2026-04-07T04:07:19Z

These stale references caused lookups to resolve to the wrong type (e.g. ImportNamespace instead of the actual function binding).

Can you actually explain it with actual code? Are there tests you can point to?

The test for this is invalidGenericWrapper/. In wrapper.ts, export const doWork = trace(_doWork) gets stored as a TypeofCallExpression. The problem is that when resolve_all copies types into the Full store, the inner references inside that expression (callee, args) keep their old Module(0) IDs, so they point at the wrong things. The module-graph snapshot diffs (e.g. test_resolve_generic_return_value.snap) show returns: Module(0) TypeId(0) becoming returns: Full TypeId(0).

The Thin→Full inner reference remapping is not required for the floating promise detection fix. Revert the module_resolver.rs changes and associated snapshot updates as requested. Made-with: Cursor

arendjr · 2026-04-15T06:55:21Z

This is a great improvement, thanks both!

github-actions Bot added A-Project Area: project A-Linter Area: linter L-JavaScript Language: JavaScript and super languages A-Type-Inference Area: type inference labels Apr 6, 2026

bmish marked this pull request as ready for review April 6, 2026 20:18

coderabbitai Bot reviewed Apr 6, 2026

View reviewed changes

Comment thread .changeset/fix-no-floating-promises-generic-wrappers.md

ematipico requested changes Apr 12, 2026

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Comment thread crates/biome_module_graph/src/js_module_info/module_resolver.rs Outdated

Comment thread crates/biome_module_graph/src/js_module_info/module_resolver.rs Outdated

Comment thread crates/biome_module_graph/src/js_module_info/module_resolver.rs Outdated

refactor: remove module_resolver remap pass per review feedback

1335923

The Thin→Full inner reference remapping is not required for the floating promise detection fix. Revert the module_resolver.rs changes and associated snapshot updates as requested. Made-with: Cursor

github-actions Bot removed the A-Project Area: project label Apr 12, 2026

ematipico approved these changes Apr 14, 2026

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ematipico merged commit f8d49d9 into biomejs:main Apr 14, 2026
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github-actions Bot mentioned this pull request Apr 14, 2026

ci: release #9890

Merged

bmish mentioned this pull request Apr 26, 2026

fix(resolver): resolve typed package main entries #10125

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fix(linter): detect floating promises through cross-module generic wrappers#9835

fix(linter): detect floating promises through cross-module generic wrappers#9835
ematipico merged 3 commits intobiomejs:mainfrom
bmish:fix/no-floating-promises-cross-module-generic-wrappers

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