Error message: "accepting non-standard pattern guards" when there are no actual patterns

This code:

{-# LANGUAGE NoPatternGuards #-}

main :: IO ()
main = print (foo 5)

foo :: Int -> Int
foo x | x < 5, x > 1 = x
      | otherwise    = -1

Produces this message:

test.hs:7:7: warning:
    accepting non-standard pattern guards (use PatternGuards to suppress this message)
        x < 5, x > 1

This is not really a "pattern guard". It's just a guard with multiple clauses, which is a syntax extension that's enabled by -XPatternGuards, but there are no patterns.

(Incidentally, I wish I could disable pattern guards to avoid the f x |x<-4 problem where a student tries to compare to negative 4 and gets an accidental pattern guard, yet still keep the multiple-clause syntax; but that's a whole different can of worms.)

Trac metadata

Trac field	Value
Version	8.6.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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