improve line info retreival (#9822)

* improve line info
* fix error message

compiler/semexprs.nim

@@ -1490,6 +1490,13 @@ proc asgnToResultVar(c: PContext, n, le, ri: PNode) {.inline.} =
 template resultTypeIsInferrable(typ: PType): untyped =
   typ.isMetaType and typ.kind != tyTypeDesc
 
+
+proc goodLineInfo(arg: PNode): TLineinfo =
+  if arg.kind == nkStmtListExpr and arg.len > 0:
+    goodLineInfo(arg[^1])
+  else:
+    arg.info
+
 proc semAsgn(c: PContext, n: PNode; mode=asgnNormal): PNode =
   checkSonsLen(n, 2, c.config)
   var a = n.sons[0]
@@ -1571,7 +1578,7 @@ proc semAsgn(c: PContext, n: PNode; mode=asgnNormal): PNode =
         else:
           typeMismatch(c.config, n.info, lhs.typ, rhsTyp)
 
-    n.sons[1] = fitNode(c, le, rhs, n.info)
+    n.sons[1] = fitNode(c, le, rhs, goodLineInfo(n[1]))
     liftTypeBoundOps(c, lhs.typ, lhs.info)
     #liftTypeBoundOps(c, n.sons[0].typ, n.sons[0].info)
 

tests/errmsgs/tshow_asgn.nim

@@ -1,7 +1,7 @@
 discard """
   errormsg: "type mismatch: got <int> but expected 'cshort = int16'"
   line: 12
-  column: 10
+  column: 27
   file: "tshow_asgn.nim"
 """