Pattern synonyms with non-conid/consym names give poor error messages

The following:

{-# LANGUAGE PatternSynonyms #-}
-- Correct: pattern P = ()
pattern p = ()

gives a rather unhelpful error message:

    parse error on input ‘=’
    Perhaps you need a 'let' in a 'do' block?
    e.g. 'let x = 5' instead of 'x = 5'

Ideally, it should hint that the name of pattern should follow constructor identifier rules.

---

In the same vein, the following:

{-# LANGUAGE PatternSynonyms #-}
-- Correct: pattern (:+) = ()
pattern (+) = ()

currently gives:

    error: parse error on input ‘+’

It should hint that the operator should begin with a :.

Trac metadata

Trac field	Value
Version	8.0.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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