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Git

Git is a decent version control(VC) system, however there are ways to make the VC process a lot smoother.

This document is best viewed from within liveview, as the charts do not render on github currently.

Terminology

topic - this is any branch that serves to fix some problem in the codebase
feature - some new concept to the codebase. Many topics can serve to fulfill one feature.
release - A release of the code. This is a git tag on main that signifies a new version of the software. This typically bumps base to the latest release as well
base - the base branch one should base work off of
main - sometimes called master, is the branch that prepares for a release.
next - a branch that has a superset of features that will be included in the next release
maint - a maintnance branch that will be updated if bugs are found
integreation branch - a topic that merges a bunch of other topics

Naming conventions

Name your topic like name/feature to avoid clashing with other people's topics.

There are some standard branches that do not follow this pattern but those are described in the Terminology section of this document

General Principles

These are some general principles which should help maintainers easily integrate your code, and have your work help out other devs on the codebase.

Do not include unrelated changes into your commits

For example, if you see some unrelated bug in the same file as your own, don't fix it in your general commit, make a new topic based on when the bug was introduced and merge that into your topic if it impacts your topic.
This makes reviewing much easier as the reviewer can read your commit message and see changes only related to that included

Make topics early and often!

This allows your work to be incrementally integrated into a release. If you put all your work into one topic, bug fixes and all, then the following will occur

The changes will not be reviewed properly
- On big projects with tight deadlines, sometimes some feature X is wanted. However if X is a single topic with a messy history, the only options are either to scrap the feature or accept it as is poor code in all.
- If this was properly split up parts of X could be merged now, with the more controversial features being held up in next, without having to sacrifice the quality of the codebase.
Other team members can not share similar work
- Often a lot of different tasks, may find the same deficiencies in the codebase.
- For a real example, let's take the following commit and topic
```
802ab9e * anoma/mariari/nock-testing-file Move the helper functions
73bfd7d * v0.3.0
 2 files changed, 44 insertions(+), 34 deletions(-)
lib/test_helper/nock.ex | 43 +++++++++++++++++++++++++++++++++++++++++++
test/nock_test.exs      | 35 +----------------------------------
```
  Here we find that we mariari moved some testing functions from test/ to lib/, as elixir tests don't share code in the best way. This allows other files in test/ to reuse the same functions that were previously found in test/nock_test.exs. In fact there are multiple topics that ended up using this. Both the executor topic and worker topic
  - 8de0c7e anoma/mariari/worker
    - 1d6bc99 anoma/mariari/executor
  both needed this. Since the worker relies upon the executor, they both don't merge in this topic separately, but if they were separate they would want to share this change.

If these changes were orchestrated by different people, then they would have made this change twice! Meaning that in the git history the work has been done in different commits! This means that when it comes time to merge in work, there will be a conflict between these two. Rather than being able to reuse other's work and save other devs time, this will come up when reviewers read the code, with unrelated changes, or when the maintainers try to merge things together and find annoying conflicts

Work can not be incrementally included
Others might just do the work before you

If one is too slow on finishing their topic and making it one big commit, then someone else might redo the same work and put it up for review, but instead of them reusing your code, they wrote it from scratch, wasting both your time and their time.

Base topics on base

Basing code on main has the following errors:

Code merged in main before a release may turn out to have issues
Git merges and conflict resolutions lead to spurious base points
Other topics can not reuse your code
Useless temporal history is had

Basing on someone's topic that you require and will merge in anyways is fine.

Code merged in main before a release may turn out to have issues

Imagine main has the following history

%%{init:
{ 'logLevel': 'debug',
  'theme': 'forest',
  'gitGraph': {'showBranches': true,
               'showCommitLabel':true,
               'mainBranchName': 'base'}} }%%
gitGraph TB:
commit id: "73bfd7d" tag: "v0.3.0"
branch Topic-Y
commit id: "4381bd3"
checkout base
merge Topic-Y id: "52b44a6"

Loading

and your code hapens to be base on 52b44a6, then the history will look something like:

%%{init:
{ 'logLevel': 'debug',
  'theme': 'forest',
  'gitGraph': {'showBranches': true,
               'showCommitLabel':true,
               'mainBranchName': 'my-cool-feature'}} }%%
gitGraph TB:
commit id: "73bfd7d" tag: "v0.3.0"
branch Topic-Y
commit id: "4381bd3"
checkout my-cool-feature
merge Topic-Y id: "52b44a6: main merge feature-y"
commit id: "7dabf44"

Loading

Later before a release, we find out that Topic-Y has issues, and any code that is based on Topic-Y will have to sit this release out. Normally to check for this, the protocol is quite simple we just:

Do not include any topics that are based on Topic-Y or merges Topic-Y into the release
Pull any topic based on Topic-Y from main

becomes muddied, as if one's topic was based on main after Topic-Y is in, then it's unclear if that topic is unaffected.

Thus my-cool-feature may be cut from the release, even if it was perfectly fine and did not rely on Topic-Y.

Git merges and conflict resolutions lead to spurious base points

Further, if we have two topics my-feature-x and my-feature-y based on main, then the history would look something like this

%%{init:
{ 'logLevel': 'debug',
  'theme': 'forest',
  'gitGraph': {'showBranches': true,
               'showCommitLabel':true,
               'mainBranchName': 'base'}} }%%
gitGraph TB:
commit id: "73bfd7d" tag: "v0.3.0"
branch main
branch ray/mnesia-attach
commit id: "97bef7"
checkout main
merge ray/mnesia-attach id: "13b3e4a"


checkout base
branch proper-topic
commit id: "8087564: add a new feature"

checkout main
branch topic-x
commit id: "bc4b2a1: new cool feature"

checkout main
merge proper-topic id: "2dd991a"

checkout main
branch topic-y
commit id: "546a8f9: add feature: conflicts X!"

checkout main
merge topic-x id: "90d91e7"
merge topic-y id: "0438922"

Loading

In a textual form this looks like:

0438922 *   main Merge branch 'topic-y'
        |\
546a8f9 | * topic-y Added a feature that conflcits with X!
90d91e7 * |   Merge branch 'topic-x'
        |\ \
        | |/
        |/|
bc4b2a1 | * topic-x Added a cool feature
2dd991a * |   Merge branch 'proper-topic'
        |\ \
        | |/
        |/|
8087564 | * proper-topic Add a new feature
13b3e4a * |   Merge branch 'ray/mnesia-attach'
        |\ \
        | |/
        |/|
97b6ef7 | * ray/mnesia-attach mnesia:
        |/
73bfd7d * v0.3.0 base

When topic-x and topic-y have a conflict, the shared base of their base is

4 taichi@Gensokyo:~/Documents/Work/Repo/anoma-all git:main: % git merge-base topic-x topic-y
13b3e4a215ea6222a1b1092ad242d3fa31e7040b

which is 13b3e4a * | Merge branch 'ray/mnesia-attach' and not 73bfd7d * v0.3.0 anoma/base, meaning that when a conflict is shown in the merge 0438922, then the diff from a 3 way diff will show the mnesia changes, potentially making it unclear to others way the potentially issues may be.

Useless temporal history is had

As we can see in the previous examples, when we base off of main, we end up in a scenario, where the date in which someone is branching is baked into the code. As maintainers we don't care about when the code was made, just the fact that it was. Thus this is a bit of history that simply adds noise

Merge other people's topics into yours

If you need some work that is already merged into next or main, simply merge that topic into yours! Since the bases are well situated, you will only deal with reasonable conflicts that you should have context for.

Base bug fixes on the commit that introduced the bug

Basing a bug fix on when the bug is introduced is superior than basing it on the latest release, as this means that it can be merged into any maint branches we may have.

For example:

73bfd7d * v0.3.0 Anoma 0.3.0
...
10f8636 * v0.2.0 Anoma 0.2.0
...
34fcd78 * v0.1.0 Release v0.1.0

if a bug was found in a topic between v0.1.0 and v0.2.0, and we based it on when the bug was found we can merge it on v0.2.0 and have v0.2.1 release from there. And have a v0.3.1 release as well.

2373834 *   v0.2.1 Merge branch 'bug-fix' into HEAD
        |\
da24431 | * bug-fix fix bug
10f8636 * | v0.2.0 Anoma 0.2.0

19c6f03 *   v0.3.1 Merge branch 'bug-fix' into HEAD
        |\
da24431 | * bug-fix fix bug
73bfd7d * | v0.3.0 Anoma 0.3.0

notice how we can merge this in with no conflicts!

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git.livemd

git.livemd

Git

Index

Git

Terminology

Naming conventions

General Principles

Do not include unrelated changes into your commits

Make topics early and often!

Base topics on base

Code merged in main before a release may turn out to have issues

Git merges and conflict resolutions lead to spurious base points

Other topics can not reuse your code

Useless temporal history is had

Merge other people's topics into yours

Base bug fixes on the commit that introduced the bug

Files

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Git

Index

Git

Terminology

Naming conventions

General Principles

Do not include unrelated changes into your commits

Make topics early and often!

Base topics on base

Code merged in main before a release may turn out to have issues

Git merges and conflict resolutions lead to spurious base points

Other topics can not reuse your code

Useless temporal history is had

Merge other people's topics into yours

Base bug fixes on the commit that introduced the bug