MLX rejects standard {|...|} strings: '' cannot be used as a quoted string delimiter

[davesnx]

Versions

• mlx: PR OCaml 5.4 #29, commit 32da854e4cfbd7da7e126f3c081b68924f5f9462
• OCaml: 5.5.0

Problem

mlx-pp rejects standard OCaml quoted strings that use an empty delimiter.

Reproduction

mlx-pp -print-ml <<'MLX'
let css = {|color: red;|}
MLX

Actual result:

Error: '' cannot be used as a quoted string delimiter,
it must contain only lowercase letters.

The same input is accepted by mlx 0.11 and by OCaml.

Impact

In a scan of 6,829 tracked Reason files converted to MLX, 2,062 outputs were rejected for this reason. It also breaks the monorepo build for existing MLX files in Siren, Grafana dashboards, and HQ.

Expected behavior is for {|...|} to parse as a quoted string with the standard empty delimiter.

[andreypopp]

Fixed on main: the 5.5 upgrade (#44) replaced the stubbed Utf8_lexeme with the real vendored implementation, which accepts empty quoted-string delimiters; the regression test from #38 landed as e5f1f79. Verified in both mlx-pp and the merlin reader.