Unhelpful error message for standalone deriving Eq instance

Summary

Adding the line

deriving instance Eq   (HsMatchContext RdrName)

after the declaration for HsMatchContext in Expr.hs results in an error, because there is no Eq instance for RdrName.

But the error is reported as

compiler/GHC/Hs/Expr.hs:2808:1: error:
    • No instance for (Eq (HsStmtContext RdrName))
        arising from a use of ‘==’
    • In the expression: ((a1 == b1))
      In an equation for ‘==’:
          (==) (StmtCtxt a1) (StmtCtxt b1) = ((a1 == b1))
      When typechecking the code for ‘==’
        in a derived instance for ‘Eq (HsMatchContext RdrName)’:
        To see the code I am typechecking, use -ddump-deriv
      In the instance declaration for ‘Eq (HsMatchContext RdrName)’
     |
2808 | deriving instance Eq   (HsMatchContext RdrName)
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Expected behavior

I would expect it to report that RdrName does not have an Eq instance.

Environment

• GHC version used: 01c43634 (technically on my wip/az/exactprint branch, but nothing has changed which should affect this.

Optional:

• Operating System:
• System Architecture: