# deno_graph

[![JSR](https://jsr.io/badges/@deno/graph)](https://jsr.io/@deno/graph)
[![Build Status - Cirrus][]][Build status] [![Twitter handle][]][Twitter badge]
[![Discord Chat](https://img.shields.io/discord/684898665143206084?logo=discord&style=social)](https://discord.gg/deno)

The module graph/dependency logic for the Deno CLI.

This repository is a Rust crate which provides the foundational code to be able
to build a module graph, following the Deno CLI's module resolution logic. It
also provides a web assembly interface to the built code, making it possible to
leverage the logic outside of the Deno CLI from JavaScript/TypeScript.

## Rust usage

### `ModuleGraph::new(...)`

`ModuleGraph::new(GraphKind::All)` creates a new module graph. From there, you
can use the `.build(...).await` method to add roots. The `build` method requires
the root module specifiers/URLs for the graph and an implementation of the
`source::Loader` trait. It also optionally takes implementation of the
`source::Resolver` trait. It will load and parse the root module and recursively
all of its dependencies, returning asynchronously a resulting `ModuleGraph`.

### `source::Loader` trait

Implementing this trait requires the `load()` method and optionally the
`get_cache_into()` method. The `load()` method returns a future with the
requested module specifier and the resulting load response. This allows the
module graph to deal with redirections, error conditions, and local and remote
content.

The `get_cache_info()` is the API for exposing additional meta data about a
module specifier as it resides in the cache so it can be part of a module graphs
information. When the graph is built, the method will be called with each
resolved module in the graph to see if the additional information is available.

### `source::Resolver` trait

This trait "replaces" the default resolution logic of the module graph. It is
intended to allow concepts like import maps and alternative resolution logic to
"plug" into the module graph.

It has two methods, `resolve` and `resolve_types`, which both have default
implementations. `resolve` takes the string specifier from the source and the
referring specifier and is expected to return a result with the resolved
specifier.

`resolve_types` takes a specifier and is expected to return a result with an
optional module specifier and optional source range of the types that should be
used. For example, if you are trying represent the `"typings"` field from a
`package.json` file, when you receive the request on `resolve_types` for the
main module of the package, you would respond with the absolute specifier to the
types along with a range that indicates the file URL to the `package.json` and
the range where it was specified. Including the range is useful to allow errors
produced from the graph to indicate "where" the dependency came from.

### `source::MemoryLoader` struct

`MemoryLoader` is a structure that implements the `source::Loader` trait and is
designed so that a cache of modules can be stored in memory to be parsed and
retrieved when building a module graph. This is useful for testing purposes or
in situations where the module contents is already available and _dynamically_
loading them is not practical or desirable.

A minimal example would look like this:

```rust
use deno_graph::ModuleSpecifier;
use deno_graph::ModuleGraph;
use deno_graph::GraphKind;
use deno_graph::source::MemoryLoader;
use deno_graph::source::Source;
use futures::executor::block_on;

fn main() {
  let mut loader = MemoryLoader::new(
    vec![
      (
        "file:///test.ts",
        Source::Module {
          specifier: "file:///test.ts",
          maybe_headers: None,
          content: "import * as a from \"./a.ts\";"
        }
      ),
      (
        "file:///a.ts",
        Source::Module {
          specifier: "file:///a.ts",
          maybe_headers: None,
          content: "export const a = \"a\";",
        }
      ),
    ],
    Vec::new(),
  );
  let roots = vec![ModuleSpecifier::parse("file:///test.ts").unwrap()];
  let future = async move {
    let mut graph = ModuleGraph::new(GraphKind::All);
    graph.build(roots, &loader, Default::default()).await;
    println!("{:#?}", graph);
  };
  block_on(future)
}
```

## Usage from Deno CLI or Deploy

See [js/README.md](js/README.md).

## Building Web Assembly

The build script (`_build.ts`) requires the Deno CLI to be installed and
available in the path. If it is, the following command should _just work_:

```
> deno task build
```

### Contributing

We appreciate your help!

To contribute, please read our
[contributing instructions](https://deno.land/manual/contributing).

This repository includes `.devcontainer` metadata which will allow a development
container to be built which has all the development pre-requisites available to
make contribution easier.

[Build Status - Cirrus]: https://github.com/denoland/deno_graph/workflows/ci/badge.svg?branch=main&event=push
[Build status]: https://github.com/denoland/deno_graph/actions
[Twitter badge]: https://twitter.com/intent/follow?screen_name=deno_land
[Twitter handle]: https://img.shields.io/twitter/follow/deno_land.svg?style=social&label=Follow