[cknitt]

Fixes #8975.

@genType let f = (c: char) => c generated export const f: (c:char) => char, and char is not a TypeScript type. Since #8892, char is an alias of int, but genType's builtin table in translate_type_expr_from_types.ml mapped only bool, int, float and string. Its Tconstr case doesn't expand abbreviations, so char fell through to a type reference named char. char now maps to number, like int.

Tests

typescript-react-example/src/Core.res gains char0 = (x: char) => x. The generated Core.gen.tsx has (x:number) => number, and yarn typecheck checks it.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Xk6AeCYpCK4SZRtHYKHGoe

[github-actions]

Semantic Diff

1 commit · Full page

Translate char to number in genType

_{7427a92 · Christoph Knittel with Claude Opus 5.5 · Oct 23, 2026}

Why

char is an alias of int since #8892, but genType's table of builtin types had no row for it and does not expand the abbreviation, so a char in a genType signature was emitted as the TypeScript type char, which does not exist.

Representation modified (genType's TypeScript type of char)

@genType
let char0 = (x: char) => x

text

-export const char0: (x:char) => char = CoreJS.char0 as any;
+export const char0: (x:number) => number = CoreJS.char0 as any;

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.22%. Comparing base (9e2f371) to head (7427a92).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8988   +/-   ##
=======================================
  Coverage   81.22%   81.22%           
=======================================
  Files         457      457           
  Lines       63862    63862           
=======================================
  Hits        51875    51875           
  Misses      11987    11987           

Files with missing lines	Coverage Δ
compiler/gentype/translate_type_expr_from_types.ml	88.46% <100.00%> (ø)

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commit: 7427a92

[github-actions]

Developer playground preview: https://rescript-lang.github.io/rescript/dev-playground/?version=pr-8988

[cknitt]

@codex review

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-23T09:27:35.955320Z	7427a92	Manual request

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