Programming

The title question is very broad, varied, and difficult. It depends.

For anything that is not a small script or small, obvious and obviously scoped takes, you can't assess at first glance.

So for a project/task/extension like you wrote it's a matter of:

Is there docs or guide specifically for what I want to do/add? If yes, the expectation is it is viable and reasonably doable with low risk.

If there is no guide the assessment is already an exploration and analysis. How is the project structured, is there docs for it or my concerns, where do I expect it as to go and what does it have to touch, what's the risks of issues and unknown difficulties and efforts. The next step would already be prototyping, and then implementing. Both of which can be started with a "let's see" and timebox approach where you remain mindful of when known or invested effort or risk increases and you can stop or rethink.

Generally mostly by cyclomatic complexity:

• How big are the methods overall

• Do methods have a somewhat single responsibility

• How is the structure, is everything inner-connected and calling each other, or are there some levels of orchestration?

• Do they have any basic unittests, so that if I want to add anything, I can copypaste some test with an entrypoint close to my modifation to see how things are going

• Bonus: they actually have linter configuration in their project, and consistent commonly used style guidelines

If the code-structure itself is good, but the formatting is bad, I can generally just run the code though a linter that fixes all the formatting. That makes it easier to use, but probably not something I'd actually contribute PRs to

How do you learn to spot these situations before diving down the rabbit hole? Or, to put it another way, what advice would you give yourself at this stage of the learning curve?

Probably some kind of metric of "If I open this code in an IDE, and add my modification, how long will it take before I can find a suitable entrypoint, and how long before I can test my changes" - if it's like half a day of debugging and diagnostics before I even can get started trying to change anything, it's seems a bit tedious

Edit: Though also, how much time is this going to save you if you do implement it? If it saves you weeks of work once you have this feature, but it takes a couple of days, I suppose it's worth going though some tedious stuff.

But then again: I'd also check: are there other similar libraries with "higher scoring" "changeability metrics"

So in your specific case:

I wanted to modify Merlin 3d printer firmware

Is there any test with a mocked 3d printer to test this, or is this a case of compiling a custom framework, installing it on your actual printer, potentially bricking it if the framework is broken - etc etc

• Use cloc to get an idea of line count.
• See how hard it is to find the entry point
• Try building it
• Try hacking a feature into it
• Try hacking a bigger feature

Thing is, for repos of any typical size, its going to take a lot more than a glance to know.

For example the Atom Editor codebase is immaculate, best formatting/commenting I've ever seen. But getting it to build is a nightmare, so its too hard to contribute to/hack.

Lots of times you just have to dive down the rabbit hole

TL;DR I look at the package first, before opening it. Unfortunately, often the packaging says a lot about the project

1. A proper README
2. A section in the README about how to setup a dev environment - without that it's often just a guessing game I don't have time for
3. A section in the README about how to deploy or run the project
4. Test cases that actually mean something, not just boilerplate assert true
5. Some kind of CI setup with steps for code quality (lint, format, type checking, ...)
6. Documentation generation
7. Pull/merge requests / external project activity

Some programming languages still have either no tooling or communities that shun it. C, C++ and PHP come to mind. Many projects from those languages are written by old folk, people who only use editors (vim, emacs, nano, ...) that don't come with tooling out of the box, or assume a might amount of things about dev machines. They are languages and communities I shun.

Go, Python, Rust, Typescript, and other languages are chock-full of developer tooling with people using IDEs or at least editors with extensions/plugins for improved developer lives. Especially Rust and Typescript are often setup with a bunch of tooling that has to be actively ignored by the developer. Often it's much easier to get started, run the project, run tests, read the code, load it into an IDE or editor with advanced language support (goto definition, refactoring, integrations for running and testing code, ...).

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How do you learn to spot these situations before diving down the rabbit hole? Or, to put it another way, what advice would you give yourself at this stage of the learning curve?

Think of the absolute simplest thing you could do that is somewhat related to your actual goal. Now do something even simpler than that. Should be easy right?

This often happens for aspiring game devs. Everyone is like "I wanna make the next <insert AAA game that had 20 million dollar budget>". But start by making Pong. Should be simple right?