# hakari

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`hakari` is the library underlying [`cargo hakari`](https://docs.rs/cargo-hakari/*), a tool to
manage `workspace-hack` packages.

## Examples

```rust
use guppy::MetadataCommand;
use hakari::{HakariBuilder, HakariOutputOptions};

// Use this workspace's PackageGraph for these tests.
let package_graph = MetadataCommand::new()
    .build_graph()
    .expect("obtained cargo-guppy's PackageGraph");

// The second argument to HakariBuilder::new specifies a Hakari (workspace-hack) package.
// In this repository, the package is called "guppy-workspace-hack".
let hakari_package = package_graph.workspace().member_by_name("guppy-workspace-hack").unwrap().id();
let hakari_builder = HakariBuilder::new(&package_graph, Some(hakari_package))
    .expect("HakariBuilder was constructed");

// HakariBuilder has a number of config options. For this example, use the defaults.
let hakari = hakari_builder.compute();

// hakari can be used to build a TOML representation that forms part of a Cargo.toml file.
// Existing Cargo.toml files can be managed using Hakari::read_toml.
let toml = hakari.to_toml_string(&HakariOutputOptions::default()).expect("TOML output was constructed");

// toml contains the Cargo.toml [dependencies] that would go in the Hakari package. It can be
// written out through `HakariCargoToml` (returned by Hakari::read_toml) or manually.
println!("Cargo.toml contents:\n{}", toml);
```

The `cargo-guppy` repository uses a workspace-hack crate managed by `cargo hakari`. [See the
generated `Cargo.toml`.](https://github.com/guppy-rs/guppy/blob/main/workspace-hack/Cargo.toml)

The `cargo-guppy` repository also has a number of fixtures that demonstrate Hakari's output.
[Here is an example.](https://github.com/guppy-rs/guppy/blob/main/fixtures/guppy/hakari/metadata_guppy_869476c-1.toml)

## How `hakari` works

Hakari follows a three-step process.

### 1. Configuration

A `HakariBuilder` provides options to configure how a Hakari computation is done. Options supported
include:
* [the location of the `workspace-hack` package](HakariBuilder::new)
* [platforms to simulate Cargo builds on](HakariBuilder::set_platforms)
* [the version of the Cargo resolver to use](HakariBuilder::set_resolver)
* [packages to be excluded during computation](HakariBuilder::add_traversal_excludes)
* [packages to be excluded from the final output](HakariBuilder::add_final_excludes)

With the optional `cli-support` feature, `HakariBuilder` options can be
[read from](HakariBuilder::from_summary) or [written to](HakariBuilder::to_summary)
a file as TOML or some other format.

### 2. Computation

Once a `HakariBuilder` is configured, its [`compute`](HakariBuilder::compute) method can be
called to create a `Hakari` instance. The algorithm runs in three steps:

1. Use guppy to [simulate a Cargo build](guppy::graph::cargo) for every workspace package and
   every given platform, with no features, default features and all features. Collect the
   results into
   [a map](internals::ComputedMap) indexed by every dependency and the different sets of
   features it was built with.
2. Scan through the map to figure out which dependencies are built with two or more
   different feature sets, collecting them into an [output map](internals::OutputMap).
3. If one assumes that the output map will be written out to the `workspace-hack` package
   through step 3 below, it is possible that it causes some extra packages to be built with a
   second feature set. Look for such packages, add them to the output map, and iterate until a
   fixpoint is reached and no new packages are built more than one way.

This computation is done in a parallel fashion, using the [Rayon](rayon) library.

The result of this computation is a `Hakari` instance.

### 3. Serialization

The last step is to serialize the contents of the output map into the `workspace-hack` package's
`Cargo.toml` file.

1. `Hakari::read_toml` reads an existing `Cargo.toml` file on disk. This file is
   *partially generated*:

   ```toml
   [package]
   name = "workspace-hack"
   version = "0.1.0"
   # more options...

   ### BEGIN HAKARI SECTION
   ...
   ### END HAKARI SECTION
   ```

   The contents outside the `BEGIN HAKARI SECTION` and `END HAKARI SECTION` lines may be
   edited by hand. The contents within this section are automatically generated.

   On success, a `HakariCargoToml` is returned.

2. [`Hakari::to_toml_string`](Hakari::to_toml_string) returns the new contents of the
   automatically generated section.
3. [`HakariCargoToml::write_to_file`](HakariCargoToml::write_to_file) writes out the contents
   to disk.

`HakariCargoToml` also supports serializing contents to memory and producing diffs.

## Future work

`hakari` is still missing a few features:

* Simulating cross-compilations
* Platform-specific excludes
* Only including a subset of packages in the final result (e.g. unifying core packages like
  `syn` but not any others)

These features will be added as time permits.

## Contributing

See the [CONTRIBUTING](../../CONTRIBUTING.md) file for how to help out.

## License

This project is available under the terms of either the [Apache 2.0 license](../../LICENSE-APACHE) or the [MIT
license](../../LICENSE-MIT).

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