How are the Manifest types used in the PNPM internals (high level overview)?

[lancejpollard]

I see in @pnpm/types there are these 4 manifest types:

• BaseManifest
• DependencyManifest
• ProjectManifest
• PackageManifest

What exactly do you mean by "manifest"? What are the differences between these 4 types of manifests? Is the PackageManifest equal to the package.json, or is it slightly different? That's basically what I'm trying to wrap my head around, what purpose these manifests serve and how they relate to the package.json.

The BaseManifest type looks like this, and looks very close to the package.json, yet there are fields which I haven't really seen in the package.json, so I'm wondering if it is a mixup of different concepts I'm unaware of?

export interface BaseManifest {
  name?: string
  version?: string
  bin?: PackageBin
  description?: string
  directories?: {
    bin?: string
  }
  files?: string[]
  dependencies?: Dependencies
  devDependencies?: Dependencies
  optionalDependencies?: Dependencies
  peerDependencies?: Dependencies
  peerDependenciesMeta?: PeerDependenciesMeta
  dependenciesMeta?: DependenciesMeta
  bundleDependencies?: string[] | boolean
  bundledDependencies?: string[] | boolean
  homepage?: string
  repository?: string | { url: string }
  scripts?: PackageScripts
  config?: object
  engines?: {
    node?: string
    npm?: string
    pnpm?: string
  }
  cpu?: string[]
  os?: string[]
  libc?: string[]
  main?: string
  module?: string
  typings?: string
  types?: string
  publishConfig?: PublishConfig
  typesVersions?: TypesVersions
  readme?: string
  keywords?: string[]
  author?: string
  license?: string
  exports?: Record<string, string>
}

For example, I just learned that the package.json has typesVersions and exports fields (among others here), but it doesn't seem to have typings or maybe it does have all these fields?

Also, what is the need for creating multiple types of manifest if they are just representations of the package.json? Could one manifest type suffice, or what am I missing?

Thank you so much for all your help in these questions!