Install dependencies from GitHub

[adlerjohn]

Problem

We would like to have a way for projects to install Sway project dependencies, so that Sway contract devs can share and re-use code. While eventually a central repository of published authenticated packages will be nice, in the meantime installing packages from simple GitHub repo URLs will suffice.

Proposal

A field in the manifest file already exists for dependencies, however only handles local dependencies.

sway/forc/src/utils/manifest.rs

Lines 28 to 46 in 8b36344

	#[derive(Deserialize, Debug)]
	#[serde(untagged)]
	pub enum Dependency {
	/// In the simple format, only a version is specified, eg.
	/// `package = "<version>"`
	Simple(String),
	/// The simple format is equivalent to a detailed dependency
	/// specifying only a version, eg.
	/// `package = { version = "<version>" }`
	Detailed(DependencyDetails),
	}
	#[derive(Deserialize, Debug)]
	#[serde(rename_all = "kebab-case")]
	pub struct DependencyDetails {
	pub(crate) version: Option<String>,
	pub(crate) path: Option<String>,
	pub(crate) git: Option<String>,
	}

These dependencies are compiled when running forc build.

sway/forc/src/ops/forc_build.rs

Lines 68 to 77 in 9569c55

	if let Some(ref deps) = manifest.dependencies {
	for (dependency_name, dependency_details) in deps.iter() {
	compile_dependency_lib(
	&this_dir,
	&dependency_name,
	&dependency_details,
	&mut namespace,
	)?;
	}
	}

forc build must be modified to additionally:

• Download missing remote git dependencies and save them locally. This can either be done with a ~/.forc directory (we only support Linux, and by coincidence macOS if it happens to work) or following Let Cargo put data into platform-specific directories rust-lang/rfcs#1615.
• Check for versions of remote git dependencies by tag (if dep on a particular tag) and hash (if dep on default branch) and update the locally-installed dependencies according to semver rules. Investigate how differences in hash play with updating.
• An --offline flag: https://doc.rust-lang.org/cargo/commands/cargo-build.html#manifest-options.
• Creation of a lockfile can be deferred to a future PR if needed.

Refs

Tracked by #27

[sezna]

I got most of that configuration manifest stuff from the Cargo repository itself. If desired, we could just continue to use that code to do this feature.

The specification of the dep: https://github.com/rust-lang/cargo/blob/2f3df16921deb34a92700f4d5a7ecfb424739558/src/cargo/core/dependency.rs#L32

The Registry abstraction: https://github.com/rust-lang/cargo/blob/e870eac9967b132825116525476d6875c305e4d8/crates/crates-io/lib.rs#L16