Historically, GNU make has not disallowed whitespace to appear in variable names.  So, when you write "$(dirname FOO)" make cannot tell the difference between a mis-typed function name and an honest attempt to expand a variable named literally "dirname FOO".

As you no doubt are aware, there's no warning or error provided when you attempt to expand a variable which doesn't exist.

This is why you don't get any notification when you mistype a function name.  You can of course enable the "--warn-undefined-variables" flag and this will cause GNU make to complain about any attempt to expand any undefined variable, including things you intended to be functions but were not.

Over the last few releases I've been deprecating the ability to create variable names containing whitespace.  Once that is fully in effect, GNU make can treat a reference containing whitespace to be an attempt to use an undefined function and generate a proper warning for it.

I'm resetting this to be an enhancement request.