fixes #5521 object variants superclass trigger bad codegen (#6120)

compiler/ccgexprs.nim

@@ -798,8 +798,7 @@ proc genRecordField(p: BProc, e: PNode, d: var TLoc) =
 
 proc genInExprAux(p: BProc, e: PNode, a, b, d: var TLoc)
 
-proc genFieldCheck(p: BProc, e: PNode, obj: Rope, field: PSym;
-                   origTy: PType) =
+proc genFieldCheck(p: BProc, e: PNode, obj: Rope, field: PSym) =
   var test, u, v: TLoc
   for i in countup(1, sonsLen(e) - 1):
     var it = e.sons[i]
@@ -811,12 +810,10 @@ proc genFieldCheck(p: BProc, e: PNode, obj: Rope, field: PSym;
     assert(disc.kind == nkSym)
     initLoc(test, locNone, it, OnStack)
     initLocExpr(p, it.sons[1], u)
-    var o = obj
-    let d = lookupFieldAgain(p, origTy, disc.sym, o)
     initLoc(v, locExpr, disc, OnUnknown)
-    v.r = o
+    v.r = obj
     v.r.add(".")
-    v.r.add(d.loc.r)
+    v.r.add(disc.sym.loc.r)
     genInExprAux(p, it, u, v, test)
     let id = nodeTableTestOrSet(p.module.dataCache,
                                newStrNode(nkStrLit, field.name.s), p.module.labels)
@@ -842,7 +839,7 @@ proc genCheckedRecordField(p: BProc, e: PNode, d: var TLoc) =
     if field.loc.r == nil: fillObjectFields(p.module, ty)
     if field.loc.r == nil:
       internalError(e.info, "genCheckedRecordField") # generate the checks:
-    genFieldCheck(p, e, r, field, ty)
+    genFieldCheck(p, e, r, field)
     add(r, rfmt(nil, ".$1", field.loc.r))
     putIntoDest(p, d, e.sons[0], r, a.storage)
   else:
@@ -1226,7 +1223,7 @@ proc genObjConstr(p: BProc, e: PNode, d: var TLoc) =
     if field.loc.r == nil: fillObjectFields(p.module, ty)
     if field.loc.r == nil: internalError(e.info, "genObjConstr")
     if it.len == 3 and optFieldCheck in p.options:
-      genFieldCheck(p, it.sons[2], r, field, ty)
+      genFieldCheck(p, it.sons[2], r, field)
     add(tmp2.r, ".")
     add(tmp2.r, field.loc.r)
     tmp2.k = locTemp

tests/types/tinheritref.nim

@@ -1,5 +1,7 @@
 discard """
-  output: "23"
+  output: '''23
+1.5
+'''
 """
 
 # bug #554, #179
@@ -25,3 +27,24 @@ type
 var
   it: TKeysIterator[int, string] = nil
 
+#bug #5521
+type
+  Texture = enum
+    Smooth
+    Coarse
+
+  FruitBase = object of RootObj
+    color: int
+    case kind: Texture
+    of Smooth:
+      skin: float64
+    of Coarse:
+      grain: int
+
+  Apple = object of FruitBase
+    width: int
+    taste: float64
+
+var x = Apple(kind: Smooth, skin: 1.5)
+var u = x.skin
+echo u