Complexity rules

What adds a decision point to a function's cyclomatic complexity, and what does not.

Every function starts at 1. Each of these adds one:

• if, elif, and else if, and Rust’s let … else.
• A ternary or conditional expression.
• Each loop: for, while, do, and Rust’s loop.
• Each case of a switch, arm of a match, or case of a Go select. Default arms add nothing: default, Rust’s _ =>, and Python’s case _:. A guarded case _ if x: still counts, and so does its guard.
• Each catch or except clause.
• Each &&, ||, and, and or, including the && of a Rust if let chain.
• Each for and if clause in a Python comprehension.

These add nothing: ?? and ?., Rust’s ?, finally, early returns, and a nested function, which is scored on its own.