contradictory-interface-assertion

Default severity: error

An assertion from one interface to another can compile even when the two method sets contain a same-named method with incompatible signatures. No dynamic type can implement both contracts, so the assertion can never succeed.

Assertions to concrete types are already checked by the Go compiler. This check focuses on interface-to-interface assertions.

Bad

type source interface { Read() int }
type target interface { Read() string }

value, ok := input.(target) // reported when input has type source

Good

type source interface { Read() int }
type target interface { Write([]byte) error }

value, ok := input.(target)