oxc-project / oxc-project/backlog

AST: ban type predicates in non-function return type positions

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Description

type t = asserts K;

https://playground.oxc.rs/?t=ir&options=%7B%22run%22%3A%7B%22lint%22%3Atrue%2C%22formatter%22%3Afalse%2C%22transform%22%3Afalse%2C%22isolatedDeclarations%22%3Afalse%2C%22whitespace%22%3Afalse%2C%22mangle%22%3Afalse%2C%22compress%22%3Afalse%2C%22scope%22%3Atrue%2C%22symbol%22%3Atrue%2C%22cfg%22%3Afalse%7D%2C%22parser%22%3A%7B%22extension%22%3A%22tsx%22%2C%22allowReturnOutsideFunction%22%3Atrue%2C%22preserveParens%22%3Atrue%2C%22allowV8Intrinsics%22%3Atrue%2C%22semanticErrors%22%3Atrue%7D%2C%22linter%22%3A%7B%7D%2C%22formatter%22%3A%7B%22useTabs%22%3Afalse%2C%22tabWidth%22%3A2%2C%22endOfLine%22%3A%22lf%22%2C%22printWidth%22%3A80%2C%22singleQuote%22%3Afalse%2C%22jsxSingleQuote%22%3Afalse%2C%22quoteProps%22%3A%22as-needed%22%2C%22trailingComma%22%3A%22all%22%2C%22semi%22%3Atrue%2C%22arrowParens%22%3A%22always%22%2C%22bracketSpacing%22%3Atrue%2C%22bracketSameLine%22%3Afalse%2C%22objectWrap%22%3A%22preserve%22%2C%22singleAttributePerLine%22%3Afalse%7D%2C%22transformer%22%3A%7B%22target%22%3A%22es2015%22%2C%22useDefineForClassFields%22%3Atrue%2C%22experimentalDecorators%22%3Atrue%2C%22emitDecoratorMetadata%22%3Atrue%2C%22optimizeEnums%22%3Atrue%2C%22optimizeConstEnums%22%3Atrue%7D%2C%22isolatedDeclarations%22%3A%7B%22stripInternal%22%3Afalse%7D%2C%22codegen%22%3A%7B%22normal%22%3Atrue%2C%22jsdoc%22%3Atrue%2C%22annotation%22%3Atrue%2C%22legal%22%3Atrue%7D%2C%22compress%22%3A%7B%7D%2C%22mangle%22%3A%7B%22topLevel%22%3Atrue%2C%22keepNames%22%3Afalse%7D%2C%22controlFlow%22%3A%7B%22verbose%22%3Afalse%7D%2C%22inject%22%3A%7B%22inject%22%3A%7B%7D%7D%2C%22define%22%3A%7B%22define%22%3A%7B%7D%7D%7D&code=type+t+%3D+asserts+K%3B

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the AST/parser handling for the TypeScript syntax shown in the issue, using the linked Oxc playground to reproduce type t = asserts K;. Trace how type predicates are accepted outside function return type positions, then add or update a parser test showing that this form is rejected while valid function return predicates remain accepted.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
52/100

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