ghc api: `load LoadAllTargets` is not idempotent

While trying to adapt hint for ghc 8.4.1, I've encountered the following phenomenon where an extra load LoadAllTargets line causes errors.

-- warning: the code below creates files A.hs and B.hs in the current working directory
import System.Directory
import Control.Monad.IO.Class
import GHCi.RemoteTypes

import GHC.Paths -- cf. the ghc-paths package
import Unsafe.Coerce

main = do
    writeFile "A.hs" "module Ahidden(a) where { a :: Int; a = 42 }"
    let mod_nameA = mkModuleName "Ahidden"
        mod_targetA = Target (TargetFile "A.hs" Nothing) False Nothing

    runGhc (Just libdir) $ do
        -- setup
        df0 <- getSessionDynFlags
        (df1, _, _) <- parseDynamicFlags df0 []
        setSessionDynFlags df1{
            ghcMode = CompManager,
            hscTarget = HscInterpreted,
            ghcLink = LinkInMemory,
            verbosity = 0
        }

        -- context : *X
        setTargets [mod_targetA]
        load LoadAllTargets
        load LoadAllTargets -- this line causes the next line to fail
        setContext [IIModule mod_nameA]
-- error:
--   ...: Could not find module ‘Ahidden’
--   Use -v to see a list of the files searched for.
        runIOExpr "print a :: IO ()"

runIOExpr e = do
    HValue h <- compileExpr e
    liftIO (unsafeCoerce h :: IO ())

This code works with ghc 8.2. The new behavior probably originates in 1893ba12, which adds flushing of the finder cache (main/Finder.hs) for every dependency analysis; my guess is that this is where the connection between the module name Ahidden and the file A.hs used be tracked.

http://lpaste.net/364298 is a less artificial example of the same behavior.

Trac metadata

Trac field	Value
Version	8.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHC API
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