Identifiers beginning with _ should not be considered for shadowing

The following program:

main = do
  let _ignored = 10
  let _ignored = 20
  return ()

Prints this warning (when compiled with, for example, -Wall):

temp.hs:3:6:
    Warning: This binding for `_ignored' shadows the existing binding
               bound at temp.hs:2:6
             In the binding group for: _ignored

In my opinion identifiers prefixed with _ should be ignored for the purposes of determining shadowing in the same way as they are ignored for the purposes of checking if something is bound but not used. So in particular, this warning would not be generated.

Trac metadata

Trac field	Value
Version	6.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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