Reject import declaration with semicolon in GHCi

Now GHCi rejects input containing an import declaration and semicolon,
and prints an appropriate error message. Before, the stuff after an
import declaration and semicolon got ignored (most of the time), without
telling the user about it. As the default behaviour of GHCi is to reject
multiple commands in a single input, we extend this behaviour to import
commands.

This patch fixes #10663.

(See https://phabricator.haskell.org/D1518 for the introduction of
`is_import` and `is_decl`.)

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1726

GHC Trac Issues: #10663

1 files changed, 12 insertions, 5 deletions

diff --git a/compiler/main/InteractiveEval.hs b/compiler/main/InteractiveEval.hs
index e1f2cfcbd0..013be3c07f 100644
--- a/compiler/main/InteractiveEval.hs
+++ b/compiler/main/InteractiveEval.hs
@@ -14,7 +14,7 @@ module InteractiveEval (
         Resume(..), History(..),
         execStmt, ExecOptions(..), execOptions, ExecResult(..), resumeExec,
         runDecls, runDeclsWithLocation,
-        isStmt, isImport, isDecl,
+        isStmt, hasImport, isImport, isDecl,
         parseImportDecl, SingleStep(..),
         resume,
         abandon, abandonAll,
@@ -89,7 +89,7 @@ import Outputable
 import FastString
 import Bag
 import qualified Lexer (P (..), ParseResult(..), unP, mkPState)
-import qualified Parser (parseStmt, parseModule, parseDeclaration)
+import qualified Parser (parseStmt, parseModule, parseDeclaration, parseImport)
 
 import System.Directory
 import Data.Dynamic
@@ -821,15 +821,22 @@ isStmt dflags stmt =
     Lexer.POk _ _ -> True
     Lexer.PFailed _ _ -> False
 
--- | Returns @True@ if passed string is an import declaration.
-isImport :: DynFlags -> String -> Bool
-isImport dflags stmt =
+-- | Returns @True@ if passed string has an import declaration.
+hasImport :: DynFlags -> String -> Bool
+hasImport dflags stmt =
   case parseThing Parser.parseModule dflags stmt of
     Lexer.POk _ thing -> hasImports thing
     Lexer.PFailed _ _ -> False
   where
     hasImports = not . null . hsmodImports . unLoc
 
+-- | Returns @True@ if passed string is an import declaration.
+isImport :: DynFlags -> String -> Bool
+isImport dflags stmt =
+  case parseThing Parser.parseImport dflags stmt of
+    Lexer.POk _ _ -> True
+    Lexer.PFailed _ _ -> False
+
 -- | Returns @True@ if passed string is a declaration but __/not a splice/__.
 isDecl :: DynFlags -> String -> Bool
 isDecl dflags stmt = do