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ocaml-ppx / ocamlformat

Auto-formatter for OCaml code
MIT License
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Feature request: support BER MetaOCaml #1211

Open ale64bit opened 4 years ago

ale64bit commented 4 years ago

Is your feature request related to a problem? Please describe. When using ocamlformat with BER MetaOCaml sources, the bracket syntax is expanded to the corresponding attributes. For example:

let _ = .<1>.

expands to

let _ = (1 [@metaocaml.bracket])

Describe the solution you'd like I guess we could argue that BER MetaOCaml is a "dialect" of OCaml and the fix doesn't belong in ocamlformat. However, it would be great if it was supported. Concretely, the bracket syntax (both bracket .<expr>. and escape .~(expr)) should be kept as is.

Additional context none

gpetiot commented 4 years ago

The problem is that we would need a way to tell the OCaml parser (that we rely on) that .<expr>. is a valid expression, formatting the corresponding attribute in the BER syntax is the easy part. Once #1026 is merged we would be able to format invalid files, so the parts where you use BER syntax would be ignored and the rest would be formatted.

Julow commented 4 years ago

@gpetiot BER MetaOCaml is a fork of OCaml. Building OCamlformat with it automatically allows to parse BER syntax, since there is no new AST nodes. This issue is about OCamlformat's output. BER parser uses [@metaocaml. ..] attributes internally but OCamlformat prints them.

I would be in favor of this feature :) I wonder how compatibility with different version would work as we rely on ocaml-migrate-parsetree ? (OCamlformat only supports 4.07 to 4.09, though)

emillon commented 4 years ago

This will at least make the test suite more complicated since we'll emit code that's invalid for the vanilla compiler, as @gpetiot said. So it would have to be gated behind a flag at least.

In any case, extensions are low priority at the moment. It would be easier to support than extensions like cppo or camlp4, but the focus for ocamlformat is vanilla ocaml code for now.

craigfe commented 3 years ago

I have a small (~50 line) patch that adds MetaOCaml dialect support here, which may be useful to anyone who just wants a quick solution. I have no comment on whether it's worth trying to maintain this upstream.

hhugo commented 1 year ago

x-link https://github.com/ocaml/ocaml/pull/11871

gpetiot commented 1 year ago

We will be happy to support this once it is merged in the compiler, we regularly rebase our vendored parser to catch up on the latest syntax.