GHCi: Fill field `DynFlags.dumpPrefix`. (Fixes #17500)

For interactive evaluations set the field `DynFlags.dumpPrefix` to the
GHCi internal module name. The GHCi module name for an interactive
evaluation is something like `Ghci9`.

To avoid user confusion, don't dump any data for GHCi internal evaluations.

Extend the comment for `DynFlags.dumpPrefix` and fix a little typo in a
comment about the GHCi internal module names.

2 files changed, 18 insertions, 2 deletions

diff --git a/ghc/GHCi/UI.hs b/ghc/GHCi/UI.hs
index 4a1b91a9fc..5beca7882d 100644
--- a/ghc/GHCi/UI.hs
+++ b/ghc/GHCi/UI.hs
@@ -458,7 +458,7 @@ interactiveUI config srcs maybe_exprs = do
    _ <- liftIO $ newStablePtr stderr
 
     -- Initialise buffering for the *interpreted* I/O system
-   (nobuffering, flush) <- initInterpBuffering
+   (nobuffering, flush) <- runInternal initInterpBuffering
 
    -- The initial set of DynFlags used for interactive evaluation is the same
    -- as the global DynFlags, plus -XExtendedDefaultRules and
@@ -1215,6 +1215,10 @@ runStmt input step = do
      -- and should therefore not be used here.
      | otherwise -> do
          hsc_env <- GHC.getSession
+         let !ic = hsc_IC hsc_env  -- Bang-pattern to avoid space leaks
+         setDumpFilePrefix ic
+           -- `-ddump-to-file` must work for normal GHCi compilations /
+           --     evaluations. (#17500)
          decls <- liftIO (hscParseDeclsWithLocation hsc_env source line input)
          run_decls decls
   where
@@ -1270,6 +1274,13 @@ runStmt input step = do
         l = L loc
       in l (LetStmt noExtField (l (HsValBinds noExtField (ValBinds noExtField (unitBag (l bind)) []))))
 
+    setDumpFilePrefix :: GHC.GhcMonad m => InteractiveContext -> m () -- #17500
+    setDumpFilePrefix ic = do
+        dflags <- GHC.getInteractiveDynFlags
+        GHC.setInteractiveDynFlags dflags { dumpPrefix = Just (modStr ++ ".") }
+      where
+        modStr = moduleNameString $ moduleName $ icInteractiveModule $ ic
+
 -- | Clean up the GHCi environment after a statement has run
 afterRunStmt :: GhciMonad m
              => (SrcSpan -> Bool) -> GHC.ExecResult -> m GHC.ExecResult
diff --git a/ghc/GHCi/UI/Monad.hs b/ghc/GHCi/UI/Monad.hs
index 87de1a83cb..b371a9b8b4 100644
--- a/ghc/GHCi/UI/Monad.hs
+++ b/ghc/GHCi/UI/Monad.hs
@@ -31,6 +31,7 @@ module GHCi.UI.Monad (
         initInterpBuffering,
         turnOffBuffering, turnOffBuffering_,
         flushInterpBuffers,
+        runInternal,
         mkEvalWrapper
     ) where
 
@@ -74,6 +75,7 @@ import Control.Monad.Trans.Reader
 import Control.Monad.IO.Class
 import Data.Map.Strict (Map)
 import qualified Data.IntMap.Strict as IntMap
+import qualified GHC.Data.EnumSet as EnumSet
 import qualified GHC.LanguageExtensions as LangExt
 
 -----------------------------------------------------------------------------
@@ -519,7 +521,10 @@ runInternal =
         -- Running GHCi's internal expression is incompatible with -XSafe.
           -- We temporarily disable any Safe Haskell settings while running
           -- GHCi internal expressions. (see #12509)
-        safeHaskell = Sf_None
+        safeHaskell = Sf_None,
+          -- Disable dumping of any data during evaluation of GHCi's internal
+          -- expressions. (#17500)
+        dumpFlags = EnumSet.empty
       }
         -- RebindableSyntax can wreak havoc with GHCi in several ways
           -- (see #13385 and #14342 for examples), so we temporarily