Common Git operations for Scala

Git has become the de facto version control system for programmers, but its core API is its command line interface, designed with a shell user foremost in mind, yet with many operations designed for batch operation, or programmatic usage. Octogenarian is an attempt to provide a Git API in Scala, with all of the capabilities available on the command-line, but presented through an idiomatic API.

• implements core Git commands
• entitities like commits, branches and tags are represented as immutable values
• Git's API is reorganized to be more idiomatic
• long-running operations run asynchronously, and track progress

Octogenarian has not yet been published. The medium-term plan is to build Octogenarian with Fury and to publish it as a source build on Vent. This will enable ordinary users to write and build software which depends on Octogenarian.

Subsequently, Octogenarian will also be made available as a binary in the Maven Central repository. This will enable users of other build tools to use it.

For the overeager, curious and impatient, see building.

All terms and types are provided in the octogenarian package:

import octogenarian.*

Octogenarian introduces various types representing entities relevant to Git.

A GitRepo is an immutable value representing a Git repository, defined only by its filesystem location: its Git directory, and optionally, its working tree. The contents of the repository are not represented by a GitRepo, and the API presumes that the repository may be changed by other processes.

The opaque types, Tag, Branch and CommitHash represent tags, branches and commit hashes within a Git repository, and all are subtypes of Refspec. Instances of these types may be returned by various Git operations, and may be used as parameters to some operations.

Commit describes the details of a commit, including its hash, tree, parent(s), author, committer, signature and message.

SshUrl is used to specify a SSH URL pointing to a remote Git repository.

Errors are represented by GitErrors, for operational problems, and GitRefErrors, for reference validation failures.

Finally, GitProcess is a mutable type representing a long-running Git process, and can be used to capture progress updates as well as the final result of an operation.

A GitRepo can be created from an existing repository on the filesystem, initializing a new one, or by cloning a remote URL.

If the repository is already on disk, constructing it is as simple as invoking the factory, GitRepo(path), where path is some representation of the path on the filesystem, as long as an appropriate Anticipation GenericPath typeclass is available. If using Galilei Paths, then it is.

A new, empty repository can be created with Git.init(path), specifying a nonexistent path on the filesystem to create it. The optional bare parameter, defaulting to false, makes it possible to create a bare Git repository, i.e. without a working tree.

A repository can also be cloned from an existing repository, either remotely or locally. The Git.clone method will clone a repository from a URL, a local path or a SshUrl, using any Anticipation-aware types, for example:

import nettlesome.*
import galilei.*

val repo = Git.clone(
  url"https://github.com/propensive/octogenarian",
  % / p"home" / p"work" / p"octogenarian",
  branch = Branch(t"main")
)

A further variant of clone exists which allows a single Commit value to be specified, cloneCommit.

Various operations are available on an instance of a GitRepo. These generally follow the naming of the Git command-line subcommands, but a single git subcommand is sometimes split into more than one method:

• checkout, checks out a Tag, Branch or CommitHash
• pull, pulls from the default remote
• switch, changes the current branch
• fetch, fetches from the specified remote
• commit, commits the currently-staged changes with the specified message
• branches, lists the branches
• makeBranch, creates a new branch
• tags, lists the repository tags
• log, reads changes to the repository as a stream of Commits
• pushTags, pushes tags to the remote

Implementations of other commands remain incomplete, and should be added in due course.

Certain operations, notably those involving fetching, will run asynchronously, and their progress can be tracked. Asynchronous operations will return a GitProcess instance. Calling its complete method will return its result synchronously, as soon as it finishes. But updates on its progress can be obtained as a LazyList[Progress] with its progress member.

Octogenarian is classified as embryotic. For reference, Soundness projects are categorized into one of the following five stability levels:

• embryonic: for experimental or demonstrative purposes only, without any guarantees of longevity
• fledgling: of proven utility, seeking contributions, but liable to significant redesigns
• maturescent: major design decisions broady settled, seeking probatory adoption and refinement
• dependable: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version 1.0.0 or later
• adamantine: proven, reliable and production-ready, with no further breaking changes ever anticipated

Projects at any stability level, even embryonic projects, can still be used, as long as caution is taken to avoid a mismatch between the project's stability level and the required stability and maintainability of your own project.

Octogenarian is designed to be small. Its entire source code currently consists of 388 lines of code.

Octogenarian will ultimately be built by Fury, when it is published. In the meantime, two possibilities are offered, however they are acknowledged to be fragile, inadequately tested, and unsuitable for anything more than experimentation. They are provided only for the necessity of providing some answer to the question, "how can I try Octogenarian?".

1. Copy the sources into your own project

   Read the fury file in the repository root to understand Octogenarian's build structure, dependencies and source location; the file format should be short and quite intuitive. Copy the sources into a source directory in your own project, then repeat (recursively) for each of the dependencies.

   The sources are compiled against the latest nightly release of Scala 3. There should be no problem to compile the project together with all of its dependencies in a single compilation.

2. Build with Wrath

   Wrath is a bootstrapping script for building Octogenarian and other projects in the absence of a fully-featured build tool. It is designed to read the fury file in the project directory, and produce a collection of JAR files which can be added to a classpath, by compiling the project and all of its dependencies, including the Scala compiler itself.

   Download the latest version of wrath, make it executable, and add it to your path, for example by copying it to /usr/local/bin/.

   Clone this repository inside an empty directory, so that the build can safely make clones of repositories it depends on as peers of octogenarian. Run wrath -F in the repository root. This will download and compile the latest version of Scala, as well as all of Octogenarian's dependencies.

   If the build was successful, the compiled JAR files can be found in the .wrath/dist directory.

Contributors to Octogenarian are welcome and encouraged. New contributors may like to look for issues marked beginner.

We suggest that all contributors read the Contributing Guide to make the process of contributing to Octogenarian easier.

Please do not contact project maintainers privately with questions unless there is a good reason to keep them private. While it can be tempting to repsond to such questions, private answers cannot be shared with a wider audience, and it can result in duplication of effort.

Octogenarian was designed and developed by Jon Pretty, and commercial support and training on all aspects of Scala 3 is available from Propensive OÜ.

In British English, a "git" is a derogatory term for a cantankerous old man, quite possibly in his eighties, and thus an octogenarian.

In general, Soundness project names are always chosen with some rationale, however it is usually frivolous. Each name is chosen for more for its uniqueness and intrigue than its concision or catchiness, and there is no bias towards names with positive or "nice" meanings—since many of the libraries perform some quite unpleasant tasks.

Names should be English words, though many are obscure or archaic, and it should be noted how willingly English adopts foreign words. Names are generally of Greek or Latin origin, and have often arrived in English via a romance language.

The logo shows a stylized version of the Git logo.

Octogenarian is copyright © 2024 Jon Pretty & Propensive OÜ, and is made available under the Apache 2.0 License.