genType emits char as a TypeScript type #8975

Found by differential semantic drift analysis from a7721303 to b123b7c3.

What is broken

genType emits char as a TypeScript type.

@genType let f = (c: char) => c generates export const f: (c:char) => char; char is not a TypeScript type, while int gives number.

• char is an alias of int since Make char an alias of int #8892 (predef.ml L424-L426).
• translate_type_expr_from_types.ml L69-L72 maps bool, int, float and string but not char, and the Tconstr case (L523) does not expand the abbreviation, so char falls through to a type named char.

The genType code is unchanged in this range, so the gap may predate it; #8892 settles what char is at runtime.

Possible cause (speculation only)

A guess: genType's builtin table predates char being an alias, and nothing tests a char in a genType signature.