fixes nim-lang#12821 (nim-lang#12822)

compiler/enumtostr.nim

@@ -41,20 +41,26 @@ proc genEnumToStrProc*(t: PType; info: TLineInfo; g: ModuleGraph): PSym =
   result.ast = n
   incl result.flags, sfFromGeneric
 
-proc searchObjCase(obj: PNode; field: PSym): PNode =
+proc searchObjCaseImpl(obj: PNode; field: PSym): PNode =
   case obj.kind
   of nkSym:
     result = nil
   of nkElse, nkOfBranch:
-    result = searchObjCase(obj.lastSon, field)
+    result = searchObjCaseImpl(obj.lastSon, field)
   else:
     if obj.kind == nkRecCase and obj[0].kind == nkSym and obj[0].sym == field:
       result = obj
     else:
       for x in obj:
-        result = searchObjCase(x, field)
+        result = searchObjCaseImpl(x, field)
         if result != nil: break
 
+proc searchObjCase(t: PType; field: PSym): PNode =
+  result = searchObjCaseImpl(t.n, field)
+  if result == nil and t.len > 0:
+    result = searchObjCase(t[0].skipTypes({tyAlias, tyGenericInst, tyRef, tyPtr}), field)
+  doAssert result != nil
+
 proc genCaseObjDiscMapping*(t: PType; field: PSym; info: TLineInfo; g: ModuleGraph): PSym =
   result = newSym(skProc, getIdent(g.cache, "objDiscMapping"), t.owner, info)
 
@@ -75,8 +81,7 @@ proc genCaseObjDiscMapping*(t: PType; field: PSym; info: TLineInfo; g: ModuleGra
   var caseStmt = newNodeI(nkCaseStmt, info)
   caseStmt.add(newSymNode dest)
 
-  let subObj = searchObjCase(t.n, field)
-  doAssert subObj != nil
+  let subObj = searchObjCase(t, field)
   for i in 1..<subObj.len:
     let ofBranch = subObj[i]
     var newBranch = newNodeI(ofBranch.kind, ofBranch.info)

tests/destructor/tcaseobj_transitions.nim

@@ -31,3 +31,19 @@ var y = MyCaseObjectB(kind: A)
 y.x = 1
 y.kind = C
 echo "no crash"
+
+
+#################
+## bug #12821
+
+type
+  RefBaseObject* = ref object of RootObj
+    case kind: bool
+      of true: a: int
+      of false: b: float
+
+  MyRefObject = ref object of RefBaseObject
+    x: float
+
+let z = new(MyRefObject)
+z.kind = false