Allow proper errors/warnings in core2core passes

This patch makes it possible for core-to-core passes to emit
proper error messages and warnings.

  * New function CoreMonad.warnMsg

  * CoreMonad.warnMsg and errorMsg now print a proper warning/error
    message heading.

  * CoreMonad carries a SrcSpan, which is used in warning/error
    messages.  It is initialised to be the source file name, but
    a core-to-core pass could set it more specifically if it had
    better location information.

There was a bit of plumbing needed to get the filename to the
right place.

4 files changed, 21 insertions, 4 deletions

diff --git a/compiler/main/ErrUtils.hs b/compiler/main/ErrUtils.hs
index 1155b4b874..3a7d9ece23 100644
--- a/compiler/main/ErrUtils.hs
+++ b/compiler/main/ErrUtils.hs
@@ -104,12 +104,25 @@ type WarnMsg = ErrMsg
 
 data Severity
   = SevOutput
-  | SevDump
+  | SevFatal
   | SevInteractive
+
+  | SevDump
+    -- Log messagse intended for compiler developers
+    -- No file/line/column stuff
+
   | SevInfo
+    -- Log messages intended for end users.
+    -- No file/line/column stuff.
+
   | SevWarning
   | SevError
-  | SevFatal
+    -- SevWarning and SevError are used for warnings and errors
+    --   o The message has a file/line/column heading,
+    --     plus "warning:" or "error:",
+    --     added by mkLocMessags
+    --   o Output is intended for end users
+
 
 instance Show ErrMsg where
     show em = errMsgShortString em
diff --git a/compiler/main/ErrUtils.hs-boot b/compiler/main/ErrUtils.hs-boot
index ac1673b367..31edcc05ee 100644
--- a/compiler/main/ErrUtils.hs-boot
+++ b/compiler/main/ErrUtils.hs-boot
@@ -5,12 +5,13 @@ import SrcLoc (SrcSpan)
 
 data Severity
   = SevOutput
-  | SevDump
+  | SevFatal
   | SevInteractive
+  | SevDump
   | SevInfo
   | SevWarning
   | SevError
-  | SevFatal
+
 
 type MsgDoc = SDoc
 
diff --git a/compiler/main/HscMain.hs b/compiler/main/HscMain.hs
index 328655c6d0..c7cabe6f9a 100644
--- a/compiler/main/HscMain.hs
+++ b/compiler/main/HscMain.hs
@@ -1643,6 +1643,8 @@ mkModGuts mod safe binds =
     ModGuts {
         mg_module       = mod,
         mg_hsc_src      = HsSrcFile,
+        mg_loc          = mkGeneralSrcSpan (moduleNameFS (moduleName mod)),
+                                  -- A bit crude
         mg_exports      = [],
         mg_deps         = noDependencies,
         mg_dir_imps     = emptyModuleEnv,
diff --git a/compiler/main/HscTypes.hs b/compiler/main/HscTypes.hs
index 7bceda50f6..b3ae6714db 100644
--- a/compiler/main/HscTypes.hs
+++ b/compiler/main/HscTypes.hs
@@ -1054,6 +1054,7 @@ data ModGuts
   = ModGuts {
         mg_module    :: !Module,         -- ^ Module being compiled
         mg_hsc_src   :: HscSource,       -- ^ Whether it's an hs-boot module
+        mg_loc       :: SrcSpan,         -- ^ For error messages from inner passes
         mg_exports   :: ![AvailInfo],    -- ^ What it exports
         mg_deps      :: !Dependencies,   -- ^ What it depends on, directly or
                                          -- otherwise