-Woperator-whitespace ignores (*), (.), and (-)

Observe:

ghci> :set -Woperator-whitespace
ghci> f = \x y -> x* y
ghci> f = \x y -> x. y
ghci> f = \x y -> x- y
ghci> f = \x y -> x+ y

<interactive>:5:14: warning: [-Woperator-whitespace]
    The suffix use of a ‘+’ might be repurposed as special syntax
      by a future language extension.
    Suggested fix: add whitespace around it.

That’s because these operators are ITstar, ITdot, and ITminus respectively, rather than ITvarsym. So they are handled by a different codepath which does not generate the warning.