Over time im inclined to value human written documentation. Especially when things involve integrations of multiple systems. I had real cases, where two parties point at code and say their code is correct. And in isolation code looks correct. But when time comes to integrate these systems. It breaks. And then if you have human readable document where intentions and expectations are specified it's much easier to come to common (working) solution.
Not all languages have capability to express complex intentions so code as documentation does not work most of the time.
Auto-generated API docs combined with handwritten documentation that covers what can't be expressed in code and includes some useful examples seems like the right approach to me. In practice that's the kind of doc I tend to have the best experience with. For example the Rust stdlib docs are auto-generated but the language also supports notes and (automatically unit-tested) examples in docstrings which means the API docs are filled with explanations & examples and mentions what assumptions are made about inputs.
https://hitchdev.com/hitchstory/
The difference between this and behave/cucumber is that the A) specification language allows for more complex representations and B) there's a templating step to generate readable documentation.
They almost convinced me somewhere in my career. But the hard truth I learnt is that most people are saying this because they aren’t capable of verbalizing what they are programming.
If your "code is doc", it should be extremely easy to add a little sentence above your method to explain what it does. And no, doc doesn’t stale. If your documentation isn’t up to what your function does, it’s probably because you should have written a brand new function instead of changing a function’s behavior.
In my experience if they can do the latter the former isn’t a problem. But since many people can’t you are left with bad code, littered with bad (often contradictory) comments which makes the problem worse not better.
First level of documentation would be specifications. Which can then be used to write tests.
But in many, many shops "Agile" means "we don't do specs anymore, woohoo!".
I completely agree with you, ie right now doing bunch of data migration code that is awful 200 lines on first look, but does quite clever transformations, handles various data corner cases, manages lots of threads, is already quite optimized (had 30x speed increase just over last week's state and not yet done with it) etc. and... is full of little green one-liners explaining why certain logic is happening, why at given place, and not elsewhere, and how it helps later in the code.
Its even one-off migration, and its mostly for me only. But I still put comments in, have enough experience to know I will keep using those comments in further optimizations, and I know by heart that many one-off efforts end up being re-used later. Code dense with logic shouldn't require you to re-read it all to have constant full mental model of it and all its branching and possibilities just because you want to tweak it a bit.
The important point is to evolve those comments with code, otherwise they become worse than no comments at all. This is where most folks hit the wall - they are simply too lazy or undisciplined for that.
I'd say that's true, and it's worth noting at this point that expressing certain things in natural language is hard. The strict rules of programming languages mean that you can reason about programs to a complexity level that would otherwise be unreachable. Notation as a tool of thought. The corollary is that there may not be a simple natural language equivalent of the code you're writing, and that adding documentation might be more effort than it's worth.
And, as you note, when integrating systems you need more than just the code and comments, since the code might not even be written with the other system in mind.
It not always feasible to document every little edge case in natural language and keep it in sync with your code. If you "document" edge cases as tests, they _have_ to be in sync with your code. It shouldn't replace traditional documentation though and is better suited for internal components and not for public API.
If the documentation can also be interpreted by machine to validate what it claims is true you have a nice side benefit, but not the reason for writing your documentation.
