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// Copyright 2018 oooutlk@outlook.com. See the COPYRIGHT // file at the top-level directory of this distribution. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! # Problem To Resolve //! //! Sometimes a crate needs to gather information from its downstream users. //! //! Frequently used mechanisms: //! //! - Cargo Features. //! //! The are friendly to cargo tools but not applicable for passing free contents //! because they are predefined options. //! //! - Environment Variables. //! //! They can pass free contents, but are not friendly to cargo tools. //! //! # Project Goal //! //! To provide a mechanism that is both friendly to cargo tools and able to pass //! free contents. //! //! # Library Overview //! //! This library helps to send metadata through the hierarchy of crates, from //! downstream crates to one of their common ancestor. //! //! The main API is `inwelling()`, which is expected to be called in `build.rs` of //! the common ancestor crate. //! //! ```text //! . +--------------> [topmost crate] //! . | 3 | ^ //! . | 4| |8 //! . | | | //! . | [dependencies] //! . |2 | | //! . | | | //! . | (metadata) |5 7| (API) //! . | | | //! . | 1 v 6 | //! . inwelling() <---- build.rs ----> bindings.rs //! .[inwelling crate] [common ancestor] //! ``` //! //! The information in section `[packages.metadata.inwelling.{common ancestor}.*]` //! in downstream crates' Cargo.toml files will be collected by `inwelling()`. //! //! # Examples //! //! See this [demo](https://github.com/oooutlk/inwelling/tree/main/src/examples/) //! for more. //! //! The `echo` crate has build-dependency of inwelling crate: //! //! ```toml //! [build-dependencies] //! inwelling = { path = "../.." } //! ``` //! //! And provides `echo()` which simply returns what it recieves as strings. //! //! In `build.rs`: //! //! ```rust,no_run //! use std::{env, fs, path::PathBuf}; //! //! fn main() { //! let metadata_from_downstream = inwelling::inwelling() //! .sections //! .into_iter() //! .fold( String::new(), |acc, section| //! format!( "{}{:?} <{}>: {}\n" //! , acc //! , section.manifest //! , section.pkg //! , section.metadata.to_string() )); //! //! let out_path = PathBuf::from( env::var( "OUT_DIR" ) //! .expect( "$OUT_DIR should exist." ) //! ).join( "metadata_from_downstream" ); //! //! fs::write( //! out_path, //! metadata_from_downstream //! ).expect( "metadata_from_downstream generated." ); //! } //! ``` //! //! In `lib.rs`: //! //! ```rust,no_run //! pub fn echo() -> String { //! include_str!( concat!( env!( "OUT_DIR" ), "/metadata_from_downstream" )) //! .to_owned() //! } //! ``` //! //! The gamma crate depends on alpha crate and conditionally depends on beta crate. //! The beta crate depends on alpha crate. The alpha, beta and gamma ccrates all //! depend on echo crate. //! //! ```text //! . +---------------> [gamma crate] gamma=true //! . | . ^ ^ //! . | gamma=true . | | //! . | . | | //! . | [beta crate] | beta=true //! . | | | | //! . | beta=true | | | //! . | | | | //! . | [alpha crate] alpha=true //! . | | | | //! . | alpha=true | | | //! . | v | | //! . inwelling() <---- build.rs ----> `echo()`----+ //! .[inwelling crate] [echo crate] //! ``` //! //! In alpha crate's test code: //! //! ```rust,no_run //! pub fn test() { //! let metadata = echo::echo(); //! assert!( metadata.find("<alpha>: {\"alpha\":true}\n").is_some() ); //! } //! ``` //! //! # Caveat //! //! Collecting metadata from downstream and utilizing it in build process makes a //! crate depending on its downstream crates. Unfortunately this kind of //! reverse-dependency is not known to cargo. As a result, the changing of metadata //! caused by modification of Cargo.toml files or changing of feature set will not //! cause recompilation of the crate collecting metadata, which it should. //! //! To address this issue, simply do `cargo clean`, or more precisely, //! `cargo clean --package {crate-collecting-metadata}` before running //! `cargo build`. Substitute `{crate-collecting-metadata}` with actual crate name, //! e.g. `cargo clean --package echo` in the examples above. use cargo_metadata::{ CargoOpt, MetadataCommand, }; use pals::Pid; use std::{ env, path::PathBuf, process, }; /// Metadata collected from downstream crates. #[derive( Debug )] pub struct Inwelling { /// sections gathered from downstream Cargo.toml files pub sections : Vec<Section>, } impl Default for Inwelling { fn default() -> Self { Inwelling{ sections: Vec::new() } } } /// Metadata collected from downstream crates, in `[package.metadata.inwelling.*]` sections. #[derive( Debug )] pub struct Section { /// name of the package which collects metadata from its downstream crates. pub pkg : String, /// path of Cargo.toml. pub manifest : PathBuf, /// metadata represented in JSON. pub metadata : serde_json::value::Value, } /// Collects metadata from `[package.metadata.inwelling.*]` sections in downstream crates' Cargo.toml files. pub fn inwelling() -> Inwelling { let mut command = MetadataCommand::new(); let mut manifest_path = PathBuf::from( env::var("PWD").unwrap() ).join( "Cargo.toml" ); let pals = pals::pals(); if let Ok( pals ) = pals { if let Some( parent ) = pals.parent_of( Pid( process::id() )) { if let Some( parent ) = pals.parent_of( parent.ppid ) { let mut argv = parent.argv(); while let Some( arg ) = argv.next() { match arg { "--all-features" => { command.features( CargoOpt::AllFeatures ); }, "--features" => if let Some( features ) = argv.next() { command.features( CargoOpt::SomeFeatures( features .split_ascii_whitespace() .map( ToOwned::to_owned ) .collect() )); }, "--no-default-features" => { command.features( CargoOpt::NoDefaultFeatures ); }, "--manifest-path" => if let Some( path ) = argv.next() { manifest_path = PathBuf::from( path ); }, _ => (), } } } } } let metadata = command .manifest_path( &manifest_path ) .exec() .unwrap(); let build_name = env::var("CARGO_PKG_NAME").unwrap(); metadata.packages.into_iter().fold( Inwelling::default(), |mut inwelling, mut pkg| { if let Some( section ) = pkg.metadata.get_mut("inwelling") { if let Some( metadata ) = section.get_mut( &build_name ) { inwelling.sections.push( Section{ pkg : pkg.name, manifest : pkg.manifest_path, metadata : metadata.take(), }); } } inwelling }) }