Support Optional Dependencies

[bristermitten]

There are many situations where dependencies may be optional. For example, users may want to only download 1 database driver based on what's in the config.

Currently, this is not possible. If a dependency isn't in the libraries directory, it is downloaded again.

My proposition is to add another field to dependencies.json (and as such Artifact) - "optional": true/false.

The default value should be false. If a dependency is optional, it will only be downloaded on initial loading(or if required transitively).

How should this be implemented?

This idea raises a few complications as to the semantics of implementation:

• How do we ensure that optional dependencies are only downloaded once?
• If the dependency graph changes, how should this be handled?
• How should dependencies be specified as optional in the Gradle plugin?
• Hypothetically, if Project depends optionally on someLibrary, how should dependency "ownership" be managed, if at all?
• Should PDM be in charge of automatically deleting unused dependencies?

The obvious solution is some sort of storage in the PluginLibraries directory. This might look something like this:

"optionals": {
    "someLibrary-version": {
        "downloaded:" "timestamp-12349875187"
    } //etc
}

If an optional dependency is present in this file, PDM can assume that it has been downloaded, and will not redownload it if not present.

A method should likely be added to PluginDependencyManager to force download all dependencies, optional ones included.