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INTERNALS.md

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Internals / architecture

The model

Mainly in Definitions.scala, Resolution.scala, and ResolutionProcess.scala.

Module

definition

Uniquely designates a... module. Typically, just an organisation (org.scala-lang) and a name (scala-library). At times, can also contains so called attributes: (unordered) key-value pairs. E.g. the SBT plugins usually have some, like scalaVersion with value 2.10 and sbtVersion with value 0.13.

Two modules having different organisation / name / attributes are simply considered different.

During resolution, all dependencies with the same module have their versions reconciled if possible. If not possible, we have a version conflict (conflicting versions of a module are needed), which makes the resolution fail.

Dependency

definition

A dependency towards a given module, with a given version (can be a version interval too, like [2.2,2.3) - TODO add support for last.revision).

TODO Add a word about the various fields of Dependency

Project

definition

Metadata about a given version of a module.

Usually comes from a POM file (Maven) or an ivy.xml file (Ivy). In the former case, the infos in Project may originate from several POMs, if the main one has a parent POM, or some import dependencies. Raw Projects are obtained from the various individual POMs, and merged back into one (done during resolution by Resolution - TODO give more details).

TODO Describe the various fields of Project

Resolution

definition

State of the resolution.

At any given point during resolution, we have:

  • ... (TODO describe the various fields)

Properties of Resolution: TODO describe the most important methods of Resolution

ResolutionProcess

definition

Proceeds with the resolution per se, starting from an initial state (a Resolution instance), until the final one.

Goes from one state to another by determining whether the current state:

  • needs some extra metadata about some versions of some modules (some IO is needed, with a cache and/or repositories), or
  • needs to take into account previously fed metadata (just calculations, no IO, giving the next state).

So each step is either IO or calculations. Several IO steps can occur in a row, if some parent POMs or dependency imports are needed to get the full picture about a given module. A calculation step is either the last step, or followed by some IO. So the steps are like: IO, IO, IO, calculations, IO, IO, calculations, IO, calculations -> done. The last step is necessarily some calculations (IO can't end it - the newly fetched metadata of an IO step needs to be taken into account by a calculation step).

TODO Describe ResolutionProcess a bit more...

Artifacts

Once the resolution is done, we get the final Resolution. This Resolutioncan provide:

  • final dependency list,
  • artifact list,
  • dependency graph,
  • ...

TODO Describe all of these a bit more

Cache / downloading

Fetching metadata

What we need during resolution: fetching metadata, possibly several ones at once.

TODO Describe the function to supply to ResolutionProcess to fetch metadata

Resolution result: artifact list

TODO How we can fetch artifacts per se...

Cache structure on disk

TODO More about the cache (structure on disk, error tracking, TTL tracking, locks)