A proposal for a PureScript Registry

Problem at hand

PureScript needs a way to distribute packages, and it's not possible to rely anymore on the Bower registry for that.

Goals for a PureScript package registry

We would like to have a registry for PureScript packages, that has the following properties:

independent: we were leaning on Bower, but that has ultimately faulted us, so we should have something that we are able to control
package uploads: we don't want a registry that just links to the location of things - like Bower - but we want to store the actual content, to prevent it from disappearing and/or being altered
content hashes: so that clients can verify package integrity when downloading them
with version bounds for packages: so that packages can express compatibilities between themselves
with a way for trusted editors to edit version bounds without republishing: so that faulty bounds can be corrected immediately without having to wait for package authors
easy to implement: the less code we have to maintain, the better
easy to secure: since this is a sensitive piece of the infrastructure, the smaller the attack surface is, the better
easy to host: we'd eventually like to have multiple copies of this registry available, so it should be easy to replicate the hosting setup

Non-goals of this design

Things we do not want to achieve with this:

all-purpose use: we are going to care about hosting PureScript packages only.
user-facing frontend: this design aims to provide a mechanism for publishing, collecting, hosting and distributing PureScript packages. The data about packages will be exposed publicly, but we do not concern ourselves with presenting it in a navigable/queriable way - this should be responsibilities of other tools/services built on top of this data.

Proposed design: "Just a GitHub Repo"

The gist of this design is that we'd have a GitHub repo (this one) to act as "the registry".

That is, the registry is a git repo, consisting in a collection of package manifests.

This repo will contain a file for every version of every package that is published. Each one of these files will contain all the info about a package at a specific version, e.g. the package name, the version, source code location, dependencies, bounds, etc This info should conform to a schema that we define as the Package type.

Features

This section is largely similar to the "goals" above, but goes a bit more in the details of our implementation. A big inspiration for this feature set has been this discussion.

Features of the current design:

immutability: packages are largely immutable - once a version has been published then its source code is forever packaged in the tarball uploaded to our storage
- ..but unpublishing will be possible for some time after publishing
- ..as well as overriding the package manifest by trustees, so that e.g. version bounds can be updated without having to ask authors to cut a new release.
ease of publishing a release is optimized for and entirely automated.
package manifests are declarative: authors need not to concern themselves with the "how", but just declare properties about their packages.
packages need not depend only on published packages in general (i.e. users can always have local/external overrides), but published packages will need to.
package manifests integrate build, package management and publishing info, a là Cabal.
no webserver: all the software running the Registry is designed in such a way that we don't need to authenticate people ourselves, nor need them to upload anything, nor need to expose any webserver in general. This greatly reduces the amount of attack vectors from the security standpoint.
first class support for Package Sets: see the relevant section for more info.

The `Package` schema

See the Package type definition for an up to date representation.

Here we embed a copy for ease of consultation:

{-

The type of a Package version in the Registry.

Note: not all fields are compulsory when compiling the definition, and we do 
provide meaningful defaults for many of them in the ./Registry.dhall file.

-}
let Map = (./Prelude.dhall).Map.Type

let Target = (./Target.dhall).Type

let Package =
      -- The name of the package
      { name : Text
      -- The SPDX code for the license under which the code is released
      , license : ./License.dhall
      -- The git repo the package is published at
      , repository : Optional ./Repo.dhall
      -- The source for the package versions listed in the `targets`.
      -- Can be either the Registry or a PackageSet
      , packages : ./Index.dhall
      -- Compilation targets for the Package
      , targets : Map Text Target
      }

in Package

It's useful to embed the definition for Target too, since it's the main component of a Package:

{-

A "compilation target".

Every target can have its own dependencies, source globs, etc.
By convention a package needs to have at least one target called `lib`.

Other common ones are `app`, `test`, `dev`, `bench`, etc. 

-}

let Map = (./Prelude.dhall).Map.Type

let TargetType =
      -- A mapping between package names (as published on the Registry or
      -- included in the Package Set) and SemVer ranges for them.
      { dependencies : Map Text Text
      -- Source globs for the local project to include in the compilation
      -- alongside its dependencies.
      , sources : List Text
      -- Optional output folder where the compiler will put its result.
      -- If not specified, the compiler will use "output"
      , output : Optional Text
      -- A target might not be pointing at the JS backend - if that's the case
      -- we can specify here the command for the alternate backend.
      -- Example values: `psgo`, `pskt`, etc.
      , backend : Optional Text
      }

let default =
      { dependencies = (toMap {=}) : Map Text Text
      , sources = [] : List Text
      , output = None Text
      , backend = None Text
      }

in  { default = default, Type = TargetType }

Adding a package to the registry

Can be done by opening a pull request to the repo - this operation can (and should) be entirely automated by the package manager the author is using.

If the author is already including a package manifest that conforms to the Package schema (in the case of a build tool using it as build manifest as well - e.g. Spago), then the only content of this file would be a Dhall import.

E.g. if we're publishing version v5.0.0 of the prelude package, then we just need to add a file called packages/prelude/v5.0.0.dhall, containing the following:

https://raw.githubusercontent.com/purescript/purescript-prelude/v5.0.0/spago.dhall

The above will import the Package manifest directly from the repo location, and it would be as if the file in this repo will have the same contents (when evaluated by Dhall).

If there's no such manifest file in the source files (as it's the case of all the packages published on the Bower registry before 2020), then we'll have to include a full fledged Package manifest here. E.g. if we'd have to import the same v5.0.0 of the prelude from Bower we'd make the following manifest in packages/prelude/v5.0.0.dhall:

let Registry = ../../v1/Registry.dhall

in  Registry.Package::{
    , name = "prelude"
    , license = Registry.License.BSD-3-Clause
    , repository = Some
        ( Registry.Repo.GitHub
            { owner = "purescript"
            , repo = "purescript-prelude"
            , version = "v5.0.0"
            }
        )
    , targets =
        toMap
          { src = Registry.Target::{
            , sources = [ "src/**/*.purs" ]
            , dependencies = [] : Registry.Dependencies
            }
          }
    }

Once the PR is open, the following will happen:

the registry curator will vet if it's good to merge
if it is, then it will merge it to master, and note that a new package version has landed in the Registry
then it goes to the relevant git tag, and fetches the sources from the package address
packages them in a tarball together with any overrides we might have for that package manifest (see the Overrides section for more details)
computes the SHA256 of the tarball
uploads the tarball and the hash to a GitHub release for hosting. Note: every package has a dedicated GitHub release that holds all the versions of that package. E.g. for the prelude package there will be a release called prelude, that holds a tarball (and its hash) for each of the versions: v4.1.1, v4.1.0, etc.
generates docs for that version and uploads them to Pursuit

Note: upgrading an existing package consists of the same process, since it involves creating a new file containing a Package manifest.

The above process covers many of the goals we defined above:

we store a copy of the packages' sources at the specified version, and this guarantees immutability for published packages (of course trusting that the registry itself would not change these)
we protect the integrity of published packages by storing their hash
we host the packages at no cost since they are normal GitHub releases
we avoid implementing authentication/authorization ourselves by piggybacking on GitHub's accounts, avoiding potential security vulnerabilities from this
we avoid implementing a backend for uploading packages, since every upload is done by the curator, that is not exposed to the public internet. This also avoids some security concerns
there's a way for "Registry Trustees" to override details about some package version - e.g. outdated version bounds - without the need for the original author to republish a package.

Downloading a package

A package manager should download packages in the following way:

fetch the tarball and the hash with the right version from the package's GitHub release in this repo
compute the SHA256 of the tarball and check that it matches the published one
unpack the tarball and use the sources as desired in the compilation process

Unpublishing a package/release

Unpublishing a version for a package can be done by removing the version file associated with it. This is allowed for security reasons (e.g. if some package was taken over maliciously), but for a different set of reasons (i.e. the leftpad problem) it's allowed only for a set period of time.

The only allowed actors that can validate/approve such unpublishing are:

the Registry Trustees
and/or the Package Author

Proposed window for possible unpublishing: one week from the publishing of that version.

Package Sets

As noted in the beginning, Package Sets are a first class citizen of this design.

We'll publish Package Sets inside this repo - you can find an example here.

Package authors/users can choose to use a Package Set rather than the Registry to be the source of the packages in their builds, and to do that they just need to assign the package key to such package set.

Example: if we have the following package manifest:

let Registry = https://raw.githubusercontent.com/purescript/registry/master/v1/Registry.dhall

in  Registry.Package::{
    , name = "my-package"
    , targets =
        toMap
          { src = Registry.Target::{
            , sources = [ "src/**/*.purs" ]
            , dependencies = toMap { effect = "^2.0.0" }
            }
          }
    }

it's pulling the effect package from the Registry, so potentially it could pick up the package effect@2.0.1 if that would get published.

But maybe we don't want that, so to use a Package Set what we have to do is to specify that in the package key, so that our manifest will change to be the following:

let Registry = https://raw.githubusercontent.com/purescript/registry/master/v1/Registry.dhall

let upstream = https://raw.githubusercontent.com/purescript/registry/master/v1/sets/20200418.dhall

in  Registry.Package::{
    , name = "my-package"
    , packages = 
        Registry.Index.PackageSet
          { compiler = upstream.compiler
          , packages = toMap upstream.packages 
          }
    , targets =
        toMap
          { src = Registry.Target::{
            , sources = [ "src/**/*.purs" ]
            , dependencies = toMap { effect = "^2.0.0" }
            }
          }
    }

..and then we'd use that package set as the provider of our package versions.

Overriding a Package

Building on the example above, what if we want to override the version of effect in the set with a local package?

We'd then change our package manifest to look like this:

let Registry = https://raw.githubusercontent.com/purescript/registry/master/v1/Registry.dhall

let upstream = https://raw.githubusercontent.com/purescript/registry/master/v1/sets/20200418.dhall

let overrides = { effect = From.Local ( ../my-effect/spago.dhall as Location ) }

in  Registry.Package::{
    , name = "my-package"
    , packages = 
        Registry.Index.PackageSet
          { compiler = upstream.compiler
          , packages = toMap (upstream.packages // overrides)
          }
    , targets =
        toMap
          { src = Registry.Target::{
            , sources = [ "src/**/*.purs" ]
            , dependencies = toMap { effect = "^2.0.0" }
            }
          }
    }

In general any Address works as an override.

This is all good for Package Sets, but how about adding local packages when just using the Registry as our provider?

It works in a similar way - e.g. to add our local copy of the effect package:

let Registry = https://raw.githubusercontent.com/purescript/registry/master/v1/Registry.dhall

let overrides = { effect = From.Local ( ../my-effect/spago.dhall as Location ) }

in  Registry.Package::{
    , name = "my-package"
    , packages = Registry.Index.Registry (toMap overrides)
    , targets =
        toMap
          { src = Registry.Target::{
            , sources = [ "src/**/*.purs" ]
            , dependencies = toMap { effect = "^2.0.0" }
            }
          }
    }

Registry Trustees and manifest editing

The "Registry Trustees" mentioned all across this document are a group of trusted janitors that have write access to this repo.

Their main task will be that of editing package manifests that will need correction - most commonly this is necessary because version bounds will be inaccurate.

But you cannot publish two different package manifests under the same package version!
That's not quite a "reproducible" build..

This is right, and in fact the Trustees will have to work under a set of constraints so that their activity will not cause disruption, unreproducible builds, etc.

First of all, if you read carefully you might notice that every package tarball has a SHA256 associated with it - we're not planning on changing that SHA ever, so we cannot actually publish a different tarball under the same version.

So how will Trustees actually be able to change manifests?

The constraints are:

we'll enforce SemVer for package versions (via CI), and authors will have the major, minor, patch and pre-release segments available to them
..while the build-metadata is reserved for Trustees to publish new versions

So to recap, when Trustees need to edit a package manifest:

they will make a new version file
change whatever is necessary to override
and bump the build-metadata in the version

Name squatting and reassigning names

I don't feel like committing to anything right now, but I'd like to have something the npm policy in this regard, where people are expected to deal with name-related matters privately first and then they are allowed to escalate to the Registry Trustees after a certain time.

Migration path

Right now we hold the Bower registry as the "source of truth" for "which package does a name refer to". This is to avoid naming inconsistencies, such as two different repos being regarded as the prelude package.

In order to provide a smooth migration path to have this Registry be the source of truth instead, we will pre-populate this new registry with all the PureScript packages existing on the Bower registry. A list of them (together with their location) can be found in the bower-packages.json file - it has been obtained by crawling the Bower registry (through libraries.io) for all the packages starting with the purescript- prefix.

For all these published packages Package manifests have been generated, and are stored in this repo. This the only thing we need in order to repackage these releases in order to upload them to the registry.

The "Registry Curator"

What we refer throughout this document as "the registry curator" is a piece of software, affectionately called pacchettibotti.

See the repo for more documentation on it. The TLDR is that it automates everything that should be automated in the Registry.

About the name: it's an "Italian-ish" pormanteau of "pacchetti" - "small packages" - and "bot". Note on pronunciation for English speakers: "che" is roughly pronounced "kae" in Italian.

Mirroring the Registry

We can think of "The Registry" as:

this git repo
all the tarballs+hashes

Mirroring it to an alternative location would consist of:

mirroring the git repo - it's just another git remote
copying all the release artifacts to another hosting location
optional, to keep the alternative location in sync: add another "tarball upload destination" to the Registry Curator

Authors of this proposal

This design is authored by @f-f, with suggestions and ideas from @reactormonk and @justinwoo

colinwahl/registry