ocaml/dune

Preprocess using both cppo and PPXs

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#171 opened on Jun 27, 2017

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help wantedpreprocessing

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Description

From https://github.com/ocsigen/lwt/issues/411#issuecomment-311214821:

it is possible to both apply a PPX and preprocess with cppo, but it requires the [separate] cppo rule stanza, and so presumably a source file with a name like foo.cppo.ml. It would be nice if one could both apply cppo and PPXs to source named foo.ml.

This is not a high priority, but it would make files like lwt_unix.cppo.ml, where we both want to use cppo, and apply Bisect_ppx, ever so slightly more maintainable.

I'm basically thinking of being able to have either multiple preprocess stanzas, or list both pps and action in one preprocess stanza. There may, of course, be other, better ways.

Contributor guide

Research direction
Investigate the current preprocess stanza implementation in dune. Look at how cppo and PPX are handled separately. Identify the code path for parsing the preprocess stanza and consider how to allow combining both (e.g., by accepting a list or using a new syntax). Look at existing tests and documentation for guidance.
Tech stack
None
Domain
build system
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
OCamldune build system
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50