New rule: Operation on Same Values

[elbrujohalcon]

Operation on Same Values

Brief Description

The idea is to emit a warning in situations where an infix operation is applied to the same value on both sides of it, like the ones below...

X = X
X == X
{A, B, C} /= {A, B, C}
A -- A
…

Should be on by default?

YES

Options

• operations :: [atom()] (default: ['=', '==', '/=', '=:=', '=/=', 'and', 'andalso', 'or', 'orelse', …])

For the default, you need to find all Erlang infix operators and figure out which ones make sense in this context and which ones doesn't. For instance, the result of X -- X is obvious ([]), but the result of X ++ X is not.

Reasoning

Paraphrasing Credo documentation:

In practice they are likely the result of a debugging session or were made by mistake.

Origin (#281)

Inspired by the Warning.OperationOnSameValues rule from Credo.
Also inspired by the Warning.BoolOperationOnSameValues rule from Credo.