Nonsense. When you read the code you need to know what it does, not what the programmer had intended, then, and only then, will you stand any hope of fixing bugs.

well chosen function and variable names tell you the intention, if it's modular enough then it will all make sense when you read it.

If people could just get over this documentation phase that programming went through in the 80's and 90's due to languages containing obtuse syntax and being so low level you had to hold a dozen things in your head at once (I'm thinking of you COM) - but in this era, with languages that operate at a high level of abstraction the era of documenting the code is over.

"The code is the documentation only works if the code is immutable."

that's actually backwards. If you want to stand any chance of changing the code then it should be readable and well structured, not well documented.