deno_graph

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:

use deno_graph::create_graph;
use deno_graph::ModuleSpecifier;
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::default();
    graph.build(roots, &mut loader, Default::default()).await;
    println!("{}", graph);
  };
  block_on(future)
}

Usage from Deno CLI or Deploy

This repository includes a compiled version of the Rust crate as Web Assembly and exposes an interface which is available via the mod.ts in this repository and can be imported like:

import * as denoGraph from "https://deno.land/x/deno_graph@{VERSION}/mod.ts";

Where {VERSION} should be substituted with the specific version you want to use.

createGraph()

The createGraph() function allows a module graph to be built asynchronously and returns a single JavaScript object containing the module graph information. It requires a root specifier or any array of root specifiers to be passed, which will serve as the roots of the module graph.

There are several options that can be passed the function in the optional options argument:

• load - a callback function that takes a URL string and a flag indicating if the dependency was required dynamically (e.g. const m = await import("mod.ts")) and resolves with a LoadResponse. By default a load() function that will attempt to load local modules via Deno.readFile() and load remote modules via fetch().
• cacheInfo - a callback function that takes a URL string and returns a CacheInfo object. In the Deno CLI, the DENO_DIR cache info is passed back using this interface. If the function is not provided, the information is not present in the module graph.
• resolve - a callback function that takes a string and a referring URL string and returns a fully qualified URL string. In the Deno CLI, import maps provide this callback functionality of potentially resolving modules differently than the default resolution.
• resolveTypes - a callback function that takes a URL string and returns the types dependency for the specifier, along with optionally the source of the types dependency. This only gets called in situations where the module is potentially untyped (e.g. JavaScript, JSX) and no other type dependency was detected. This is intended to enrich the module graph with external types that are resolved in some other fashion, like from a package.json or via detecting an @types typings package is available.

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.

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.