fixes #10203 (#10290)

* fixes #10203
* make typredef test green again
* fixes the regressions differently

compiler/semtypes.nim

@@ -1318,7 +1318,19 @@ proc semGeneric(c: PContext, n: PNode, s: PSym, prev: PType): PType =
   if tx != result and tx.kind == tyObject and tx.sons[0] != nil:
     semObjectTypeForInheritedGenericInst(c, n, tx)
 
-proc maybeAliasType(c: PContext; typeExpr, prev: PType): PType
+proc maybeAliasType(c: PContext; typeExpr, prev: PType): PType =
+  if typeExpr.kind in {tyObject, tyEnum, tyDistinct, tyForward} and prev != nil:
+    result = newTypeS(tyAlias, c)
+    result.rawAddSon typeExpr
+    result.sym = prev.sym
+    assignType(prev, result)
+
+proc fixupTypeOf(c: PContext, prev: PType, typExpr: PNode) =
+  if prev != nil:
+    let result = newTypeS(tyAlias, c)
+    result.rawAddSon typExpr.typ
+    result.sym = prev.sym
+    assignType(prev, result)
 
 proc semTypeExpr(c: PContext, n: PNode; prev: PType): PType =
   var n = semExprWithType(c, n, {efDetermineType})
@@ -1422,20 +1434,6 @@ proc semProcTypeWithScope(c: PContext, n: PNode,
     when useEffectSystem: setEffectsForProcType(c.graph, result, n.sons[1])
   closeScope(c)
 
-proc maybeAliasType(c: PContext; typeExpr, prev: PType): PType =
-  if typeExpr.kind in {tyObject, tyEnum, tyDistinct} and prev != nil:
-    result = newTypeS(tyAlias, c)
-    result.rawAddSon typeExpr
-    result.sym = prev.sym
-    assignType(prev, result)
-
-proc fixupTypeOf(c: PContext, prev: PType, typExpr: PNode) =
-  if prev != nil:
-    let result = newTypeS(tyAlias, c)
-    result.rawAddSon typExpr.typ
-    result.sym = prev.sym
-    assignType(prev, result)
-
 proc symFromExpectedTypeNode(c: PContext, n: PNode): PSym =
   if n.kind == nkType:
     result = symFromType(c, n.typ, n.info)

compiler/types.nim

@@ -432,7 +432,7 @@ proc typeToString(typ: PType, prefer: TPreferedDesc = preferName): string =
        sfAnon notin t.sym.flags:
     if t.kind == tyInt and isIntLit(t):
       result = t.sym.name.s & " literal(" & $t.n.intVal & ")"
-    elif t.kind == tyAlias:
+    elif t.kind == tyAlias and t.sons[0].kind != tyAlias:
       result = typeToString(t.sons[0])
     elif prefer in {preferName, preferTypeName} or t.sym.owner.isNil:
       result = t.sym.name.s

tests/objects/tobject.nim

@@ -17,3 +17,23 @@ suite "object basic methods":
     check($obj == "(foo: 1)")
   test "it should test equality based on fields":
     check(makeObj(1) == makeObj(1))
+
+# bug #10203
+
+type
+  TMyObj = TYourObj
+  TYourObj = object of RootObj
+    x, y: int
+
+proc init: TYourObj =
+  result.x = 0
+  result.y = -1
+
+proc f(x: var TYourObj) =
+  discard
+
+var m: TMyObj = init()
+f(m)
+
+var a: TYourObj = m
+var b: TMyObj = a