Structural equality for the side-effect-free expressions a self-comparison can involve:
identifiers, member access, indexing (by an equal index), binary operations, elementary-type
casts, payable(...), the pure unary operators (-, !, ~), and the ternary c ? a : b.
Anything else (notably arbitrary calls, which may return different values or have side effects,
and the ++/-- unary ops, which mutate) is treated as unequal, so the lint never fires on a
comparison whose two sides could legitimately differ.