Error reporting on obsolete file

I have just had this warning:

Whatever.hs:41:1: warning: [-Wunused-imports]
    The import of ‘Data.Map’ is redundant
      except perhaps to import instances from ‘Data.Map’
    To import instances alone, use: import Data.Map()
   |
41 | import Data.Foldable
   | ^^^^^^^^^^^^^^^^^^^^^

This happens because the source file has been modified during the compilation: GHC shows an excerpt of the new file to report an error in the old file. Could we cache the old file somehow during the compilation to avoid this discrepancy?

Trac metadata

Trac field	Value
Version	8.2.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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