microsoft / microsoft/TypeScript
Template Literal with infer does not handle surrogate pairs
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Description
TypeScript Version: 4.1.0-dev.20201015
Search Terms:
template literal, surrogate pair, infer
Code
type Head<StrT extends string> = StrT extends `${infer HeadT}${string}` ? HeadT : never;
type Tail<StrT extends string> = StrT extends `${string}${infer TailT}` ? TailT : never;
type TestHead = Head<"𡁻">
type TestTail = Tail<"𡁻">
Expected behavior:
Should handle surrogate pairs properly
Actual behavior:
Playground Link:
Playground
Related Issues:
Searched for "template literal surrogate pair" and didn't find anything
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Reproduce the issue with the Head and Tail type aliases and the surrogate-pair string "𡁻" in the linked TypeScript Playground or TypeScript 4.1.0-dev.20201015. Trace template-literal infer handling in the compiler; done means both aliases preserve the complete surrogate pair rather than splitting it.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 38/100