partial fix for #1119

Unless we're in one-shot mode, emit an error if we attempt to
demand-load interfaces for home modules.  This can only happen in one
way (that I'm aware of): typing a qualified name at the GHCi prompt
that refers to a module that isn't loaded.  Previously you got a
cryptic message about not finding an interface file, now you get:

Prelude> Foo.a

<interactive>:1:0:
    attempting to use module `Foo' (Foo.hs) which is not loaded

Of course you can still refer to package modules like this without
loading them explicitly, only home modules are affected, and the
behaviour is exactly the same as if you try to ':browse Foo' and
Foo isn't loaded.

diff --git a/compiler/iface/LoadIface.lhs b/compiler/iface/LoadIface.lhs
index cfb8f12..6b2660d 100644 (file)
--- a/compiler/iface/LoadIface.lhs
+++ b/compiler/iface/LoadIface.lhs
@@ -51,6 +51,7 @@ import Outputable
 import BinIface
 import Panic
 
+import Control.Monad (when)
 import Data.List
 import Data.Maybe
 import Data.IORef
@@ -175,9 +176,9 @@ loadInterface doc_str mod from
                        -- The (src_imp == mi_boot iface) test checks that the already-loaded
                        -- interface isn't a boot iface.  This can conceivably happen,
                        -- if an earlier import had a before we got to real imports.   I think.
-           other -> do
+           other -> do {
 
-       { let { hi_boot_file = case from of
+          let { hi_boot_file = case from of
                                ImportByUser usr_boot -> usr_boot
                                ImportBySystem        -> sys_boot
 
@@ -412,18 +413,25 @@ findAndReadIface doc_str mod hi_boot_file
 
        -- Look for the file
        ; hsc_env <- getTopEnv
-       ; mb_found <- ioToIOEnv (findHiFile hsc_env mod hi_boot_file)
+       ; mb_found <- ioToIOEnv (findExactModule hsc_env mod)
        ; case mb_found of {
-             Failed err -> do
+              
+             err | notFound err -> do
                { traceIf (ptext SLIT("...not found"))
                ; dflags <- getDOpts
                ; returnM (Failed (cannotFindInterface dflags 
                                        (moduleName mod) err)) } ;
-
-             Succeeded file_path -> do 
+             Found loc mod -> do 
 
        -- Found file, so read it
-       { traceIf (ptext SLIT("readIFace") <+> text file_path)
+       { let { file_path = addBootSuffix_maybe hi_boot_file (ml_hi_file loc) }
+
+        ; if thisPackage dflags == modulePackageId mod
+                && not (isOneShot (ghcMode dflags))
+            then returnM (Failed (homeModError mod loc))
+            else do {
+
+        ; traceIf (ptext SLIT("readIFace") <+> text file_path)
        ; read_result <- readIface mod file_path hi_boot_file
        ; case read_result of
            Failed err -> returnM (Failed (badIfaceFile file_path err))
@@ -433,18 +441,10 @@ findAndReadIface doc_str mod hi_boot_file
                | otherwise ->
                  returnM (Succeeded (iface, file_path))
                        -- Don't forget to fill in the package name...
-       }}}
-
-findHiFile :: HscEnv -> Module -> IsBootInterface
-          -> IO (MaybeErr FindResult FilePath)
-findHiFile hsc_env mod hi_boot_file
-  = do
-      maybe_found <- findExactModule hsc_env mod
-      case maybe_found of
-       Found loc mod -> return (Succeeded path)
-               where
-                  path = addBootSuffix_maybe hi_boot_file (ml_hi_file loc)
-       err -> return (Failed err)
+       }}}}
+
+notFound (Found _ _) = False
+notFound _ = True
 \end{code}
 
 @readIface@ tries just the one file.
@@ -689,5 +689,12 @@ wrongIfaceModErr iface mod_name file_path
            ]
        ]
   where iface_file = doubleQuotes (text file_path)
+
+homeModError mod location
+  = ptext SLIT("attempting to use module ") <> quotes (ppr mod)
+    <> (case ml_hs_file location of
+           Just file -> space <> parens (text file)
+           Nothing   -> empty)
+    <+> ptext SLIT("which is not loaded")
 \end{code}