Use SrcSpan from the binder as initial source estimatewip/source-note-fixes

There are some situations where we end up with no source notes in useful
positions in an expression. In this case we currently fail to provide
any source information about where an expression came from.

This patch improves the initial estimate by using the position from the
top-binder as the guess for the location of the whole inner expression.
It provides quite a course estimate but it's better than nothing.

Ticket #20847

1 files changed, 8 insertions, 1 deletions

diff --git a/compiler/GHC/Stg/Debug.hs b/compiler/GHC/Stg/Debug.hs
index 8452642288..7eb4155068 100644
--- a/compiler/GHC/Stg/Debug.hs
+++ b/compiler/GHC/Stg/Debug.hs
@@ -69,7 +69,14 @@ collectStgBind (StgRec pairs) = do
 
 collectStgRhs :: Id -> StgRhs -> M StgRhs
 collectStgRhs bndr (StgRhsClosure ext cc us bs e)= do
-  e' <- collectExpr e
+  let
+    name = idName bndr
+    -- If the name has a span, use that initially as the source position in-case
+    -- we don't get anything better.
+    with_span = case nameSrcSpan name of
+                  RealSrcSpan pos _ -> withSpan (pos, occNameString (getOccName name))
+                  _ -> id
+  e' <- with_span $ collectExpr e
   recordInfo bndr e'
   return $ StgRhsClosure ext cc us bs e'
 collectStgRhs _bndr (StgRhsCon cc dc _mn ticks args) = do