Fixes #3691.

compiler/transf.nim

@@ -707,12 +707,14 @@ proc transformExceptBranch(c: PTransf, n: PNode): PTransNode =
     let excTypeNode = n[0][1]
     let actions = newTransNode(nkStmtList, n[1].info, 2)
     # Generating `let exc = (excType)(getCurrentException())`
+    # -> getCurrentException()
     let excCall = PTransNode(callCodegenProc("getCurrentException", ast.emptyNode))
+    # -> (excType)
     let convNode = newTransNode(nkHiddenSubConv, n[1].info, 2)
     convNode[0] = PTransNode(ast.emptyNode)
     convNode[1] = excCall
     PNode(convNode).typ = excTypeNode.typ.toRef()
-
+    # -> let exc = ...
     let identDefs = newTransNode(nkIdentDefs, n[1].info, 3)
     identDefs[0] = PTransNode(n[0][2])
     identDefs[1] = PTransNode(ast.emptyNode)
@@ -720,15 +722,14 @@ proc transformExceptBranch(c: PTransf, n: PNode): PTransNode =
 
     let letSection = newTransNode(nkLetSection, n[1].info, 1)
     letSection[0] = identDefs
-
+    # Place the let statement and body of the 'except' branch into new stmtList.
     actions[0] = letSection
     actions[1] = transformSons(c, n[1])
+    # Overwrite 'except' branch body with our stmtList.
     result[1] = actions
 
     # Replace the `Exception as foobar` with just `Exception`.
     result[0] = result[0][1]
-  #debug(PNode(result))
-  #echo(PNode(result))
 
 proc dontInlineConstant(orig, cnst: PNode): bool {.inline.} =
   # symbols that expand to a complex constant (array, etc.) should not be