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

6 files changed, 29 insertions, 10 deletions

diff --git a/compiler/main/GHC.hs b/compiler/main/GHC.hs
index 31f809c716..2dad92a482 100644
--- a/compiler/main/GHC.hs
+++ b/compiler/main/GHC.hs
@@ -132,7 +132,7 @@ module GHC (
 
         -- ** Other
         runTcInteractive,   -- Desired by some clients (Trac #8878)
-        isStmt, isImport, isDecl,
+        isStmt, hasImport, isImport, isDecl,
 
         -- ** The debugger
         SingleStep(..),
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
diff --git a/ghc/GHCi/UI.hs b/ghc/GHCi/UI.hs
index 7bd9bbeb77..1303af554f 100644
--- a/ghc/GHCi/UI.hs
+++ b/ghc/GHCi/UI.hs
@@ -933,12 +933,21 @@ enqueueCommands cmds = do
 runStmt :: String -> SingleStep -> GHCi (Maybe GHC.ExecResult)
 runStmt stmt step = do
   dflags <- GHC.getInteractiveDynFlags
-  if | GHC.isStmt dflags stmt   -> run_stmt
-     | GHC.isImport dflags stmt -> run_imports
-     | otherwise                -> run_decl
+  if | GHC.isStmt dflags stmt    -> run_stmt
+     | GHC.isImport dflags stmt  -> run_import
+     -- Every import declaration should be handled by `run_import`. As GHCi
+     -- in general only accepts one command at a time, we simply throw an
+     -- exception when the input contains multiple commands of which at least
+     -- one is an import command (see #10663).
+     | GHC.hasImport dflags stmt -> throwGhcException
+       (CmdLineError "error: expecting a single import declaration")
+     -- Note: `GHC.isDecl` returns False on input like
+     -- `data Infix a b = a :@: b; infixl 4 :@:`
+     -- and should therefore not be used here.
+     | otherwise                 -> run_decl
 
   where
-    run_imports = do
+    run_import = do
       addImportToContext stmt
       return (Just (GHC.ExecComplete (Right []) 0))
 
diff --git a/testsuite/tests/ghci/scripts/T10663.script b/testsuite/tests/ghci/scripts/T10663.script
new file mode 100644
index 0000000000..10be57f52a
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T10663.script
@@ -0,0 +1 @@
+import Data.List; sort [2, 1]
\ No newline at end of file
diff --git a/testsuite/tests/ghci/scripts/T10663.stderr b/testsuite/tests/ghci/scripts/T10663.stderr
new file mode 100644
index 0000000000..7170dbf29c
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T10663.stderr
@@ -0,0 +1 @@
+error: expecting a single import declaration
\ No newline at end of file
diff --git a/testsuite/tests/ghci/scripts/all.T b/testsuite/tests/ghci/scripts/all.T
index da0ea0d55e..06a91259a8 100755
--- a/testsuite/tests/ghci/scripts/all.T
+++ b/testsuite/tests/ghci/scripts/all.T
@@ -225,6 +225,7 @@ test('T10466', normal, ghci_script, ['T10466.script'])
 test('T10501', normal, ghci_script, ['T10501.script'])
 test('T10508', normal, ghci_script, ['T10508.script'])
 test('T10520', normal, ghci_script, ['T10520.script'])
+test('T10663', normal, ghci_script, ['T10663.script'])
 test('T10989',
     [
       extra_clean(['dummy.hs', 'dummy.lhs', 'dummy.tags'])