fix #18977; disallow change branch of an object variant in ORC (#21526)

* fix #18977 disallow change branch of an object variant in ORC

* check errors for goto exception

* fixes conditions

* fixes tests

* add a test case for #18977

tests/arc/t18977.nim

@@ -0,0 +1,26 @@
+discard """
+  matrix: "--mm:arc"
+"""
+
+type
+  E = enum
+    a, b, c, d
+  X = object
+    v: int
+  O = object
+    case kind: E
+    of a:
+      a: int
+    of {b, c}:
+      b: float
+    else:
+      d: X
+
+proc `=destroy`(x: var X) =
+  echo "x destroyed"
+
+var o = O(kind: d, d: X(v: 12345))
+doAssert o.d.v == 12345
+
+doAssertRaises(FieldDefect):
+  o.kind = a

tests/arc/tcaseobj.nim

@@ -60,7 +60,7 @@ proc `=destroy`(o: var TMyObj) =
     o.p = nil
     echo "myobj destroyed"
 
-proc `=`(dst: var TMyObj, src: TMyObj) =
+proc `=copy`(dst: var TMyObj, src: TMyObj) =
   `=destroy`(dst)
   dst.p = alloc(src.len)
   dst.len = src.len
@@ -170,18 +170,24 @@ proc test_myobject =
   x.x1 = "x1"
   x.x2 = "x2"
   x.y1 = "ljhkjhkjh"
-  x.kind1 = true
+  {.cast(uncheckedAssign).}:
+    x.kind1 = true
   x.y2 = @["1", "2"]
-  x.kind2 = true
+  {.cast(uncheckedAssign).}:
+    x.kind2 = true
   x.z1 = "yes"
-  x.kind2 = false
+  {.cast(uncheckedAssign).}:
+    x.kind2 = false
   x.z2 = @["1", "2"]
-  x.kind2 = true
+  {.cast(uncheckedAssign).}:
+    x.kind2 = true
   x.z1 = "yes"
   x.kind2 = true # should be no effect
   doAssert(x.z1 == "yes")
-  x.kind2 = false
-  x.kind1 = x.kind2 # support self assignment with effect
+  {.cast(uncheckedAssign).}:
+    x.kind2 = false
+  {.cast(uncheckedAssign).}:
+    x.kind1 = x.kind2 # support self assignment with effect
 
   try:
     x.kind1 = x.flag # flag is not accesible
@@ -207,8 +213,9 @@ type
       error*: string
 
 proc init(): RocksDBResult[string] =
-  result.ok = true
-  result.value = "ok"
+  {.cast(uncheckedAssign).}:
+    result.ok = true
+    result.value = "ok"
 
 echo init()
 
@@ -222,7 +229,8 @@ type MyObj = object
     of true: x1: string
 
 var a = MyObj(kind: false, x0: 1234)
-a.kind = true
+{.cast(uncheckedAssign).}:
+  a.kind = true
 doAssert(a.x1 == "")
 
 block:

tests/arc/tcaseobjcopy.nim

@@ -169,18 +169,23 @@ proc test_myobject =
   x.x1 = "x1"
   x.x2 = "x2"
   x.y1 = "ljhkjhkjh"
-  x.kind1 = true
+  {.cast(uncheckedAssign).}:
+    x.kind1 = true
   x.y2 = @["1", "2"]
-  x.kind2 = true
+  {.cast(uncheckedAssign).}:
+    x.kind2 = true
   x.z1 = "yes"
-  x.kind2 = false
+  {.cast(uncheckedAssign).}:
+    x.kind2 = false
   x.z2 = @["1", "2"]
-  x.kind2 = true
+  {.cast(uncheckedAssign).}:
+    x.kind2 = true
   x.z1 = "yes"
   x.kind2 = true # should be no effect
   doAssert(x.z1 == "yes")
-  x.kind2 = false
-  x.kind1 = x.kind2 # support self assignment with effect
+  {.cast(uncheckedAssign).}:
+    x.kind2 = false
+    x.kind1 = x.kind2 # support self assignment with effect
 
   try:
     x.kind1 = x.flag # flag is not accesible
@@ -206,7 +211,8 @@ type
       error*: string
 
 proc init(): RocksDBResult[string] =
-  result.ok = true
+  {.cast(uncheckedAssign).}:
+    result.ok = true
   result.value = "ok"
 
 echo init()
@@ -221,7 +227,8 @@ type MyObj = object
     of true: x1: string
 
 var a = MyObj(kind: false, x0: 1234)
-a.kind = true
+{.cast(uncheckedAssign).}:
+  a.kind = true
 doAssert(a.x1 == "")
 
 block:

tests/destructor/tgotoexceptions7.nim

@@ -25,7 +25,8 @@ proc helper = doAssert(false)
 
 proc main(i: int) =
   var obj = Obj(kind: kindA, s: "abc")
-  obj.kind = kindB
+  {.cast(uncheckedAssign).}:
+    obj.kind = kindB
   obj.i = 2
   try:
     var objA = ObjA()