W0007 - Trivial Match

Error

-module(main).

do_foo() ->
    X = 42,
    Y = 42,
    X = X,
%%% ^^^^^ warning: match is redundant
    X = Y.

Explanation

The error message is indicating that the statement X = X is redundant.

Since the pattern (the part on the left of the = and the expression (the part on the right of the =) are the same and given that in Erlang variables are immutable (once a value is assigned to a variable it cannot be changed), the operation will always succeed.

To fix this warning, you should remove the redundant assignment.