Fossil

Update of "Fossil-NG"
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Overview

Artifact ID: f3025d965453bd78f3c83a7cc804a5063f8136c18feae77cb4a0e44eda741160
Page Name:Fossil-NG
Date: 2019-05-09 11:13:57
Original User: wyoung
Mimetype:text/x-markdown
Parent: a489846a77cb08b8f0e19e7104634dd09cec8973b0b15a70c1cfbab41fded153 (diff)
Next e973562b41e1bae76eae39a39617791a998143cf1d74b7f3a3496e605453c08c
Content

Status

This is a discussion format and record of ideas for "Fossil: The Next Generation" or Fossil-NG. There is currently no code in place for Fossil-NG.

Broadly, this document collects ideas that have come up since Fossil was created in 2006 which are difficult enough to build atop the current design that solving them might involve a breakage in compatibility with prior Fossil versions. Much as the hash policy feature forced the change from Fossil 1.x to Fossil 2.0, implementing some of the following ideas might force a similarly epochal shift to "Fossil 3.0" or "Fossil 4.0".

Goals

Partial Clones and Syncs

Fossil is currently limited to complete clones and complete syncs. This has several drawbacks in real-world workflows which are solved by features allowing partial clones and syncs:

Better Git Integration

Although Fossil is nearly as old as Git and several other popular DVCSes, Git has emerged as the dominant DVCS though various market forces, rather than on purely technical merit. (See Fossil vs. Git.)

This is unfortunate, because of the various version control systems available today, Git is the least user-friendly.

Nevertheless, Fossil must have some level of accommodation with this reality.

Fossil 2.x currently has several features in this line, primarily the longstanding fossil import --git command and the much newer fossil git export command. (The latter replaces the old fossil export --git command, deprecated in Fossil 2.9.)

There are still some missing pieces, however. We'd like to be able to:

Realize in evaluating all of these ideas that the primary and most important purpose of Fossil is to support the development of the SQLite project, and it lhas succeeded fabulously in that respect. Any changes implemented for Fossil-NG must respect that history. In particular, Fossil-NG must be able to import the complete SQLite history intact, without any changes to hash identifiers.

VCS as File Container

One way to think about a VCS is as a enhanced file container. You can use file container formats like tar and zip to create a single snapshot of a project. A VCS is the same except that it allows one to store multiple snapshots.

Fossil-NG should have facilities that allow you to work with Fossil repositories in as simple a manner as traditional command-line file archiving tools like tar and zip. For example:

fossil new new-repo.fossil Makefile README.md src/

That command will create a file container named "new-repo.fossil" that contains the files Makefile, README.md, and all files under src/. This repository would be compact, and suitable for sending as an email attachment, just like one would do with a tarball or ZIP archive.

The SQLite Archiver project shows how to build a file container using SQLite for storage. Fossil-NG should include the capabilities of SQLite Archiver, though the underlying file format will doubtless be more advanced so that it can also support block-chain versioning.

Current Fossil provides web-page links and command-line operations for generating a ZIP archive or tarball for a particular check-in. Fossil-NG should continue to have that capability, but should also be able to generate a single-checkin repository that serves as a file container.

Support For Multiple VCS Formats

Fossil-NG should provide the ability to store artifacts in various formats:

  1. Git
  2. Mercurial
  3. Legacy Fossil
  4. Fossil-NG

This is a generalization of the Git-specific cases above: in principle, Fossil is not tied to a single file format. It is possible to encode a Fossil repository atop other substrates other than the current SQLite-based DB file format.

A repository that contains only Git-formatted artifacts should have the capability to interoperate seamlessly with Git repositories. This allows, for example, a Fossil-NG user to clone and use a repository out of GitHub while continuing to use the superior Fossil user interface. It also allows a Fossil server to answer clone/push/pull requests from legacy Git clients. The same symmetry applies to Mercurial and legacy Fossil.

Thus, by using a single Fossil-NG client and user interface, a developer can interact with legacy repositories in a variety of formats, without having to learn the idiosyncrasies of multiple VCSes.

Fossil-NG itself will be able to operate on repositories that hold a mixture of artifacts in various formats. Legacy Git, Hg, and Fossil clients, however will only be able to interoperate with Fossil-NG repositories that hosts all artifacts in the one format the the client understands.

Converting artifacts from one format to another is an expensive computation - too expensive to do on-the-fly. However, it is conceivable that Fossil-NG could be used to convert repositories between Git/Hg/Fossil formats as an off-line operation.