Improve Linting in GHCi (fixes Trac #8215)

The original problem was that we weren't bringing varaibles bound in the
interactive context into scope before Linting the result of a top-level
declaration in GHCi.  (We were doing this for expressions.)

Moreover I found that we weren't Linting the result of desugaring
a GHCi expression, which we really should be doing.

It took me a bit of time to unravel all this, and I did some refactoring
to make it easier next time.

  * CoreMonad contains the Lint wrappers that get the right
    environments into place.  It always had endPass and lintPassResult
    (which Lints bindings), but now it has lintInteractiveExpr.

  * Both use a common function CoreMonad.interactiveInScope to find
    those in-scope variables.

Quite a bit of knock-on effects from this, but nothing exciting.

1 files changed, 18 insertions, 5 deletions

diff --git a/compiler/coreSyn/CoreLint.lhs b/compiler/coreSyn/CoreLint.lhs
index 68aaea5b5c..1913e3ab93 100644
--- a/compiler/coreSyn/CoreLint.lhs
+++ b/compiler/coreSyn/CoreLint.lhs
@@ -16,7 +16,7 @@ A ``lint'' pass to check for Core correctness
 
 {-# OPTIONS_GHC -fprof-auto #-}
 
-module CoreLint ( lintCoreBindings, lintUnfolding ) where
+module CoreLint ( lintCoreBindings, lintUnfolding, lintExpr ) where
 
 #include "HsVersions.h"
 
@@ -120,14 +120,15 @@ find an occurence of an Id, we fetch it from the in-scope set.
 
 
 \begin{code}
-lintCoreBindings :: CoreProgram -> (Bag MsgDoc, Bag MsgDoc)
+lintCoreBindings :: [Var] -> CoreProgram -> (Bag MsgDoc, Bag MsgDoc)
 --   Returns (warnings, errors)
 -- If you edit this function, you may need to update the GHC formalism
 -- See Note [GHC Formalism]
-lintCoreBindings binds
+lintCoreBindings local_in_scope binds
   = initL $ 
-    addLoc TopLevelBindings $
-    addInScopeVars binders  $
+    addLoc TopLevelBindings        $
+    addInScopeVars local_in_scope  $
+    addInScopeVars binders         $
 	-- Put all the top-level binders in scope at the start
 	-- This is because transformation rules can bring something
 	-- into use 'unexpectedly'
@@ -178,6 +179,18 @@ lintUnfolding locn vars expr
     (_warns, errs) = initL (addLoc (ImportedUnfolding locn) $
                             addInScopeVars vars	           $
                             lintCoreExpr expr)
+
+lintExpr :: [Var]		-- Treat these as in scope
+	 -> CoreExpr
+	 -> Maybe MsgDoc	-- Nothing => OK
+
+lintExpr vars expr
+  | isEmptyBag errs = Nothing
+  | otherwise       = Just (pprMessageBag errs)
+  where
+    (_warns, errs) = initL (addLoc TopLevelBindings $
+                            addInScopeVars vars	    $
+                            lintCoreExpr expr)
 \end{code}
 
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