feat(compiler): accept truthy filter predicates - #153
Merged
Conversation
`.filter(fn)` required the callback to return exactly bool. JS applies ToBoolean to whatever the predicate answers, so `xs.filter((s) => s)` — the idiomatic drop-the-falsy — was refused for no semantic reason. The filter loop now wraps the call in the same toBool an `if` statement would apply. A bool answer is unchanged and emits identical IR. A union answer routes through its interned per-arm truthy helper, requested at the call site where a real node exists for the diagnostic. A unit-only answer is constantly falsy, and the call still runs for its effects. The kinds with no native ToBoolean keep the fence: void has no value at all, and dyn/jsval/caught truthiness needs the embedded engine. Verified against Node: filtering strings, numbers, and a `(string | undefined)[]` all print identically in both. Diagnostics 100, filter corpus 9 across both backends.
|
The latest updates on your projects. Learn more about Vercel for GitHub.
|
![vercel[bot]](https://avatars.githubusercontent.com/in/8329?s=60&v=4){kind=small}
ctate
approved these changes
Aug 14, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Summary
Array.prototype.filterpredicate results and lower them throughToBooleanvoidpredicates, including static, island-backed, and checked-dynamic arraysValidation
pnpm exec vitest run tests/harness/diagnostics.test.tspnpm exec vitest run tests/harness/differential.test.ts --testNamePattern "2683-filter-truthy-predicate"pnpm exec vitest run packages/compiler/test/ts7/order-parity.test.ts