[fix #18977] disallow change branch of an object variant in ARC again

compiler/ccgstmts.nim

@@ -1559,10 +1559,9 @@ proc asgnFieldDiscriminant(p: BProc, e: PNode) =
   initLocExpr(p, e[0], a)
   getTemp(p, a.t, tmp)
   expr(p, e[1], tmp)
-  if optTinyRtti notin p.config.globalOptions:
-    let field = dotExpr[1].sym
-    genDiscriminantCheck(p, a, tmp, dotExpr[0].typ, field)
-    message(p.config, e.info, warnCaseTransition)
+  let field = dotExpr[1].sym
+  genDiscriminantCheck(p, a, tmp, dotExpr[0].typ, field)
+  message(p.config, e.info, warnCaseTransition)
   genAssignment(p, a, tmp, {})
 
 proc genAsgn(p: BProc, e: PNode, fastAsgn: bool) =

compiler/injectdestructors.nim

@@ -396,15 +396,16 @@ It is best to factor out piece of object that needs custom destructor into separ
       return
 
     # generate: if le != tmp: `=destroy`(le)
-    let branchDestructor = produceDestructorForDiscriminator(c.graph, objType, leDotExpr[1].sym, n.info, c.idgen)
-    let cond = newNodeIT(nkInfix, n.info, getSysType(c.graph, unknownLineInfo, tyBool))
-    cond.add newSymNode(getMagicEqSymForType(c.graph, le.typ, n.info))
-    cond.add le
-    cond.add tmp
-    let notExpr = newNodeIT(nkPrefix, n.info, getSysType(c.graph, unknownLineInfo, tyBool))
-    notExpr.add newSymNode(createMagic(c.graph, c.idgen, "not", mNot))
-    notExpr.add cond
-    result.add newTree(nkIfStmt, newTree(nkElifBranch, notExpr, c.genOp(branchDestructor, le)))
+    when false:
+      let branchDestructor = produceDestructorForDiscriminator(c.graph, objType, leDotExpr[1].sym, n.info, c.idgen)
+      let cond = newNodeIT(nkInfix, n.info, getSysType(c.graph, unknownLineInfo, tyBool))
+      cond.add newSymNode(getMagicEqSymForType(c.graph, le.typ, n.info))
+      cond.add le
+      cond.add tmp
+      let notExpr = newNodeIT(nkPrefix, n.info, getSysType(c.graph, unknownLineInfo, tyBool))
+      notExpr.add newSymNode(createMagic(c.graph, c.idgen, "not", mNot))
+      notExpr.add cond
+      result.add newTree(nkIfStmt, newTree(nkElifBranch, notExpr, c.genOp(branchDestructor, le)))
   result.add newTree(nkFastAsgn, le, tmp)
 
 proc genWasMoved(c: var Con, n: PNode): PNode =

tests/arc/tcaseobj.nim

@@ -206,8 +206,10 @@ type
       error*: string
 
 proc init(): RocksDBResult[string] =
-  result.ok = true
-  result.value = "ok"
+  result = RocksDBResult[string](ok: true, value: "ok")
+  # fixme: use {.cast(uncheckedAssign).}
+  # result.ok = true
+  # result.value = "ok"
 
 echo init()
 
@@ -221,8 +223,9 @@ type MyObj = object
     of true: x1: string
 
 var a = MyObj(kind: false, x0: 1234)
-a.kind = true
-doAssert(a.x1 == "")
+# fixme: use {.cast(uncheckedAssign).}
+# a.kind = true
+# doAssert(a.x1 == "")
 
 block:
   # bug #15532

tests/arc/tcaseobjcopy.nim

@@ -206,8 +206,10 @@ type
       error*: string
 
 proc init(): RocksDBResult[string] =
-  result.ok = true
-  result.value = "ok"
+  result = RocksDBResult[string](ok: true, value: "ok")
+  # fixme: use {.cast(uncheckedAssign).}
+  # result.ok = true
+  # result.value = "ok"
 
 echo init()
 
@@ -221,8 +223,9 @@ type MyObj = object
     of true: x1: string
 
 var a = MyObj(kind: false, x0: 1234)
-a.kind = true
-doAssert(a.x1 == "")
+# fixme: use {.cast(uncheckedAssign).}
+# a.kind = true
+# doAssert(a.x1 == "")
 
 block:
   # bug #15532

tests/destructor/tgotoexceptions7.nim

@@ -1,6 +1,8 @@
 discard """
   cmd: "nim c --gc:arc --exceptions:goto --panics:off $file"
-  output: '''prevented!
+  output: '''
+field error prevented
+prevented!
 caught
 AssertionDefect
 900'''
@@ -25,8 +27,10 @@ proc helper = doAssert(false)
 
 proc main(i: int) =
   var obj = Obj(kind: kindA, s: "abc")
-  obj.kind = kindB
-  obj.i = 2
+  try:
+    obj.kind = kindB
+  except FieldDefect:
+    echo "field error prevented"
   try:
     var objA = ObjA()
     bplease(ObjB(objA))