Printed @as names of fields and constructors turn non-ASCII letters into other characters #9142

When a type declaration is printed (error messages, hover, createInterface), the @as names of record fields and variant constructors are escaped the OCaml way (%S in Printtyp.tree_of_constructor, String.escaped in Res_outcome_printer). Non-ASCII bytes become decimal escapes like \195\169, which ReScript reads back as different characters.

module Make = (X: {type t}) => {
  type record = {@as("prénom") name: X.t}
  type variant = | @as("é") E | @as("a\"b") Q
}

module Applied = Make({
  type t = string
})

createInterface prints the types of Applied through this printer:

module Applied: {
  type record = {@as("pr\195\169nom") name: string}
  type variant = @as("\195\169") E | @as("a\"b") Q
}

Read back, @as("pr\195\169nom") names the field prénom:

type record = {@as("pr\195\169nom") name: string}
let r = {name: "x"}

compiles to

let r = {
  "prénom": "x"
};

so a generated interface gives the fields and constructors other runtime names than the implementation. Error messages and hover show the escapes too.

The @tag name of a declaration is printed with String_literal.encode_js_string since #9136, which keeps non-ASCII letters and escapes only what a string literal needs.