Inwelling 0.4.0: more reliable to support dependency injection

[oooutlk]

What's New

The crate inwelling has been upgraded to version 0.4.0. It become more reliable, without the need of spawning commands to analyze program arguments, environment variables nor cargo metadata. Instead of using cargo_metadata, serde_json and pals, it adopts toml as the only dependency. This upgrade is caused by a real use case which this crate desires, for verification and improving. So if you find crate inwelling useful in some cases, please let me know.

Project Goal

To provide a mechanism for upstream crates to collect information from downstream crates.

Use cases

Case 1, anonymous struct

Rust does not provide anonymous struct yet. To simulate this feature, we want to define the struct's fields and access to its value at the same place. The upstream crate providing anonymous struct simulation must know all the ad-hoc structs among its downstream crates source code, to define them before downstream crates start to compile.

Case 2, get rid of the multiple -sys crates

It would be nice if we have a unified method of compiling APIs from "the C world" instead of maintain multiple -sys crates. And same APIs which are defined in the same header files may be separated in different -sys crates, e.g. tcl_sys::TCL_OK and tk_sys::TCL_OK. Some crate such as cib tries provide a unified method to compile C libraries and provides a unified namespace clib::.

Information collected from downstream crates

Invoking collect_downstream() will collect the following information from crates which called register() in its build.rs.

• Package name.

• Metadata defined in Cargo.toml.

• Manifest paths of Cargo.toml.

• Source file paths(optional). Call collect_downstream() with the argument
  inwelling::Opt::dump_rs_paths == true to collect.

Quickstart

1. The upstream crate e.g. crate foo calls inwelling::collect_downstream() in its build.rs and do whatever it want to generate APIs for downstream.

2. The downstream crate e.g. crate bar calls inwelling::register() in its build.rs.

// build.rs
fn main() { inwelling::register(); }

To send some metadata to upstream, encode them in Cargo.toml's package metadata.

[package.metadata.inwelling.foo]
answer = { type = "integer", value = "42" }