Fix the format idempotency of open type declarations

[barkmadley]

e.g.

  type a = b = ..;

was being formatted as

  type a = .. = b;

[jordwalke]

You are at it again!

[jordwalke]

I assume you ran into this issue in a real world app. How are you pulling in your custom fixes into your personal project so that these don't become blockers for you?

[barkmadley]

To be honest, I'm not even sure what the form type x = ..; is used for, I've never had to reach for the feature myself in my OCaml work.

I just decided to increase the unit test code coverage for the reason_pprint_ast.ml file. I integrated bisect into my local dev build and am slowly going through the uncovered lines. So far I have 3 other test cases that increase coverage but this one uncovered an actual bug so I thought I wouldn't wait to create a PR.

[jordwalke]

That's awesome. Thanks for helping us improve the quality of the code.

I'm curious how you are finding code that is not executed in the formatting tests. Is there an OCaml utility you are using?

[jordwalke]

By the way type t = ..; is a cool feature called extensible variants. It allows one place to define the start of a type, and then allows multiple other modules that depend on it, to extend that type - without any of the extenders having to know about each other. It's a great utility for implementing plugin systems that can inject themselves into a system, where all the plugins don't need to know about each other.

[barkmadley]

Ah so thats how extensible variants are defined. Back in my day we wrote our plugin systems with first class modules. It worked pretty well.

To get code coverage reports I

1. opam install bisect_ppx
2. add the (preprocess (pps (bisect_ppx))) line to the reason-parser/jbuild file:

3. make test (jbuilder will rebuild everything correctly which is awesome) this generates a bunch of bisect_XXXX.out
4. generate a coverage report using bisect-ppx-report -ignore-missing-files -I _build/ -html coverage/ bisect*.out ./*/*/*/bisect*.out (and then I usually clear out the bisect.out files using a find/rm command.

The report looks like this:

I will probably add a makefile target to make this process a bit easier. At the moment I'm relying on shell history to not forget anything.

[jordwalke]

I would definitely use such a makefile target.