jakstys.lt/content/log/2022/git-subtrac.md

---
title: "zig, git-subtrac and dependencies"
date: 2022-04-23T05:37:51+03:00
draft: true
---

TLDR: modern programming languages make it very easy to add many dependencies.
That is nice for development, but a nightmare for maintenance. Unfortunately,
zig is following suit. I wish we could accept that adding dependencies does not
have to be trivial. If we accept that, thanks to ubiquity of git, we may have
almost solved the dependency problem.

Adding dependencies
-------------------

All of the programming languages I've used professionally whose name does not
start with "c"[^1]  have package managers[^2], which make "dependency
management" easy. These package managers will, as part of the project's build
process, download and build the dependencies, making adding and using
third-party dependencies easy.

Because C/C++ still does not have a universal package manager, not adding
external dependencies to C/C++ is the path of least resistance. Instead, it is
common to rely on libraries already installed in the system. Because of this
cultural difference, there is a plethora of dependency managers that will
discover, but not install dependencies: autotools, cmake, pkg-config and
others. As a result, C/C++ projects I've been involved usually had 0-5
non-system dependencies, whereas non-C/C++ projects -- tens, hundreds or
thousands[^3]. Having many system dependencies is painful for user experience,
so (the good) C/C++ projects also avoid having too many of them.

Not doing things that are easy to do requires discipline: brushing teeth,
limiting candy intake, not adding dependencies all over the place. If it is
easy to add dependencies and there is no discipline not doing so, the project
will gain a lot of dependency "weight" with time.

{{<img src="_cheese/2022/brick-house.jpg"
    alt="House made out of Duplo pieces"
    caption="Just like this brick house, \"modern\" package managers are optimized for building, not maintenance. Photo mine, house by my sons."
    hint="photo"
    >}}

In Go and Python small number of dependencies is often a sign of care and
quality. [mattn/go-sqlite3](https://github.com/mattn/go-sqlite3),
[uber/zap](https://github.com/uber-go/zap),
[apenwarr/redo](https://github.com/apenwarr/redo) and
[django](https://djangoproject.com) are good examples. Making it easy to depend
on external code is is convenient during development, but frees developers from
their basic right (or obligation?) to audit understand them. And adds real
long-term maintenance costs.

The costs of just having dependencies are huge. I haven't done a survey and
have only my experience to base this on (read: "many anecdotes of me failing to
build stuff I wrote a decade ago"). But it is bad enough that I have a
dependency checklist and am prepared to do grunt work to avoid or strip it.
Here is my checklist:

- Obvious: does it work at all?
- How easy is it to build, run and run it's tests?
- Is it well written? API surface, documentation, tests, error handling, error
  signaling, logging, metrics (if applicable), etc.
- It's system dependencies.
- It's transitive dependencies.

If a dependency is well written, but has more transitive dependencies than I
need and there is no good alternative, I will fork it and remove unnecessary
code and dependencies. My recent example is
[sql-migrate](https://github.com/motiejus/sql-migrate).

To sum up, the "modern" languages optimize for initial development experience,
not maintenance. And as [Corbet says][linux-rust]. "We can't understand why
Kids These Days just don't want to live that way". Kids want to build, John,
not maintain. A 4-letter Danish corporation made a fortune by selling toys that
do not need to be maintained: they are designed to be disassembled and built
anew. It is very hard to change the guts of an existing structure without
rebuilding it.

If I may combine Corbet's views with mine: if we understand and audit our
dependencies (and transitive ones), we will have less dependencies and a more
maintainable system. Win-win.

Which brings us to...

Transitive dependencies and git-subtrac
---------------------------------------

[`git-subtrac`][git-subtrac] does not deal with transitive dependencies. At
least not directly. Or I am not aware of it. Ok, I haven't tried.

If we audit and thus understand our dependencies, we will be able to add
transitive ones to our project even without support of git-subtrac. So perhaps
git-subtrac shouldn't care?

I use [`git-subtrac`][git-subtrac] for some of my projects, and am not very
enthusiastic about Zig getting it's own package manager (can we all use
git-subtrac and be done with it?). A few weeks ago in a park in Milan my
conversation with [Andrew Kelley](https://andrewkelley.me/) was something like:

- me: "git-subtrac yadda yadda yadda submodules but better yadda yadda yadda".
- Andrew: "if I clone a repository that uses it with no extra parameters, will
  it work as expected?"
- me: "no, you have to pass `--recursive`, so git will checkout submodules...
  even if they are already fetched."
- Andrew: "then it's a piece-of-shit-approach."

Uh, I agree. People have not grown muscle memory to clone repositories with
`--recursive` flag and never will, so it's impossible to adopt git-subtrac
beyond well-controlled silos. Which is why we will have a
yet-another-programming-language-specific-package-manager, this time for zig.
Or at least my argument for using git-subtrac stops right there.

Why git-subtrac?
----------------

[`git-subtrac`][git-subtrac] is like "classic" git submodules, but all refs of
the dependencies stay in the same repository. Wait, stop here. Repeat after me:
_it is git submodules, but all refs stay in the same repository_. I also call
it "good vendoring". Since all the deps are in our repo, no external force can
make our dependency unavailable.

It is, howerver, harder to *add* a dependency with submodules than with, say,
`go get <dependency>`. Let's talk about adding dependencies.

Conclusion
----------

Can git checkout local submodules when they are in the same repository, so our
conversation of reconsidering (or not having) a zig package manager doesn't
stop after 5 seconds?

[^1]: Alphabetically: Erlang, Go, Java, Javascript, PHP, Perl, Python.
[^2]: Usually written in the same language. Zoo of package managers (sometimes
  a couple of popular ones for the same programming language) is a can of worms
  in an on itself worth another blog post.
[^3]: `go.sum` of a project I am currently involved clocks around 6k lines.
  This is quite a lot for Go, but still peanuts to Node.js.

[git-subtrac]: https://github.com/apenwarr/git-subtrac/
[linux-rust]: https://lwn.net/SubscriberLink/889924/a733d6630e3b5115/