describe-dune: convert dune project to a compact JSON description

describe-dune finds dune files in the directory and extracts their library and file dependencies.

Produced mapping doesn't perfectly match to dune structure in handling file dependencies. It's assumed that all stanzas in a dune file depend on the very same set of files, whereas in reality they might be not. It may lead to a circular dependency appearing in file dependency analysis whereas on level of stanzas there is none. This file dependency simplification is kept to ease format and semantics. It's a advised to change structure of a project if two dune files cross-depend on generated files.

JSON format

In schema below: "relative path" is a path relative to "src" key, while absolute is a path relative to project's root.

Generates a json array with one entry per non-empty dune file discovered (for dune files with no relevant stanzas no entries are added):

[
  {
    "src": "path to directory containing a dune file",
    "subdirs": [ "relative path to subdirs containing a non-empty dune file" ],
    "units": [
      {
        "name": "name of a compilation unit",
        "public_name": "public name of a compilation unit",
        "type": "lib | exe | test",
        "deps": [ "ocaml library name" ],
        "package": "name of a package",
        "has_inline_tests": true,
        "modules": {
          "with_standard": false,
          "include": [ "module name to include" ],
          "exclude": [ "module name to exclude" ]
        },
        "implements": "name of a virtual library",
        "default_implementation": "name of a default implementation library"
      }
    ],
    "file_deps": [ "absolute path" ],
    "file_outs": { "absolute path of a file generated": "promote | standard | fallback" }
  }
]

Field file_deps contains only dependencies that are outside the dune file directory. Relatedly, file_outs declares only generated files on which some other dune files are dependent.

Some fields of a unit object (like public_name) are omitted if not specified by the dune file. Modules field represents a subset of syntax allowed by dune, namely at most one :standard meta-module with some files listed for inclusion and exclusion.

Thanks

A big source of inspiration for this project was opam2json.