Windows: print an error message in addDLL

Also, look for libXXX.dll in addition to XXX.dll (see #1883, this
isn't really a proper fix, but it'll help in some cases).
And I tidied up the error message for a DLL load failure, though it's
still a bit of a mess because addDLL is supposed to return a (static)
string with the error message, but this isn't possible on Windows.

2 files changed, 28 insertions, 17 deletions

diff --git a/compiler/ghci/Linker.lhs b/compiler/ghci/Linker.lhs
index 459fbd9e90..5d01b9a71f 100644
--- a/compiler/ghci/Linker.lhs
+++ b/compiler/ghci/Linker.lhs
@@ -456,21 +456,20 @@ preloadLib dflags lib_paths framework_paths lib_spec
   where
     preloadFailed :: String -> [String] -> LibrarySpec -> IO ()
     preloadFailed sys_errmsg paths spec
-       = do maybePutStr dflags
-    	       ("failed.\nDynamic linker error message was:\n   " 
-                    ++ sys_errmsg  ++ "\nWhilst trying to load:  " 
-                    ++ showLS spec ++ "\nDirectories to search are:\n"
-                    ++ unlines (map ("   "++) paths) )
-            give_up
+       = do maybePutStr dflags "failed.\n"
+            ghcError $
+	      CmdLineError (
+                    "user specified .o/.so/.DLL could not be loaded ("
+                    ++ sys_errmsg ++ ")\nWhilst trying to load:  "
+                    ++ showLS spec ++ "\nAdditional directories searched:"
+                    ++ (if null paths then " (none)" else
+                        (concat (intersperse "\n" (map ("   "++) paths)))))
     
     -- Not interested in the paths in the static case.
     preload_static _paths name
        = do b <- doesFileExist name
             if not b then return False
                      else loadObj name >> return True
-    
-    give_up = ghcError $ 
-	      CmdLineError "user specified .o/.so/.DLL could not be loaded."
 \end{code}
 
 
diff --git a/rts/Linker.c b/rts/Linker.c
index a9c145b6e8..26d671e6e9 100644
--- a/rts/Linker.c
+++ b/rts/Linker.c
@@ -1066,14 +1066,19 @@ addDLL( char *dll_name )
    sprintf(buf, "%s.DLL", dll_name);
    instance = LoadLibrary(buf);
    if (instance == NULL) {
-	 sprintf(buf, "%s.DRV", dll_name);	// KAA: allow loading of drivers (like winspool.drv)
-	 instance = LoadLibrary(buf);
-	 if (instance == NULL) {
-		stgFree(buf);
-
-	    /* LoadLibrary failed; return a ptr to the error msg. */
-	    return "addDLL: unknown error";
-   	 }
+       if (GetLastError() != ERROR_MOD_NOT_FOUND) goto error;
+       // KAA: allow loading of drivers (like winspool.drv)
+       sprintf(buf, "%s.DRV", dll_name);
+       instance = LoadLibrary(buf);
+       if (instance == NULL) {
+           if (GetLastError() != ERROR_MOD_NOT_FOUND) goto error;
+           // #1883: allow loading of unix-style libfoo.dll DLLs
+           sprintf(buf, "lib%s.DLL", dll_name);
+           instance = LoadLibrary(buf);
+           if (instance == NULL) {
+               goto error;
+           }
+       }
    }
    stgFree(buf);
 
@@ -1089,6 +1094,13 @@ addDLL( char *dll_name )
 #  else
    barf("addDLL: not implemented on this platform");
 #  endif
+
+error:
+   stgFree(buf);
+   sysErrorBelch(dll_name);
+               
+   /* LoadLibrary failed; return a ptr to the error msg. */
+   return "addDLL: could not load DLL";
 }
 
 /* -----------------------------------------------------------------------------