renamed '=' to '=copy' [backport:1.2] (#15585)

* Assign hook name changed to `=copy`
* Adapt destructors.rst
* [nobackport] Duplicate tests for =copy hook
* Fix tests
* added a changelog entry

Co-authored-by: Clyybber <darkmine956@gmail.com>

tests/arc/tcaseobjcopy.nim

@@ -0,0 +1,246 @@
+discard """
+  valgrind: true
+  cmd: "nim c --gc:arc -d:useMalloc $file"
+  output: '''myobj destroyed
+myobj destroyed
+myobj destroyed
+A
+B
+begin
+end
+prevented
+(ok: true, value: "ok")
+myobj destroyed
+'''
+"""
+
+# bug #13102
+
+type
+  D = ref object
+  R = object
+    case o: bool
+    of false:
+      discard
+    of true:
+      field: D
+
+iterator things(): R =
+  when true:
+    var
+      unit = D()
+    while true:
+      yield R(o: true, field: unit)
+  else:
+    while true:
+      var
+        unit = D()
+      yield R(o: true, field: unit)
+
+proc main =
+  var i = 0
+  for item in things():
+    discard item.field
+    inc i
+    if i == 2: break
+
+main()
+
+# bug #13149
+
+type
+  TMyObj = object
+    p: pointer
+    len: int
+
+proc `=destroy`(o: var TMyObj) =
+  if o.p != nil:
+    dealloc o.p
+    o.p = nil
+    echo "myobj destroyed"
+
+proc `=copy`(dst: var TMyObj, src: TMyObj) =
+  `=destroy`(dst)
+  dst.p = alloc(src.len)
+  dst.len = src.len
+
+proc `=sink`(dst: var TMyObj, src: TMyObj) =
+  `=destroy`(dst)
+  dst.p = src.p
+  dst.len = src.len
+
+type
+  TObjKind = enum Z, A, B
+  TCaseObj = object
+    case kind: TObjKind
+    of Z: discard
+    of A:
+      x1: int # this int plays important role
+      x2: TMyObj
+    of B:
+      y: TMyObj
+
+proc testSinks: TCaseObj =
+  result = TCaseObj(kind: A, x1: 5000, x2: TMyObj(len: 5, p: alloc(5)))
+  result = TCaseObj(kind: B, y: TMyObj(len: 3, p: alloc(3)))
+
+proc use(x: TCaseObj) = discard
+
+proc testCopies(i: int) =
+  var a: array[2, TCaseObj]
+  a[i] = TCaseObj(kind: A, x1: 5000, x2: TMyObj(len: 5, p: alloc(5)))
+  a[i+1] = a[i] # copy, cannot move
+  use(a[i])
+
+let x1 = testSinks()
+testCopies(0)
+
+# bug #12957
+
+type
+  PegKind* = enum
+    pkCharChoice,
+    pkSequence
+  Peg* = object ## type that represents a PEG
+    case kind: PegKind
+    of pkCharChoice: charChoice: ref set[char]
+    else: discard
+    sons: seq[Peg]
+
+proc charSet*(s: set[char]): Peg =
+  ## constructs a PEG from a character set `s`
+  result = Peg(kind: pkCharChoice)
+  new(result.charChoice)
+  result.charChoice[] = s
+
+proc len(a: Peg): int {.inline.} = return a.sons.len
+proc myadd(d: var Peg, s: Peg) {.inline.} = add(d.sons, s)
+
+proc sequence*(a: openArray[Peg]): Peg =
+  result = Peg(kind: pkSequence, sons: @[])
+  when false:
+    #works too:
+    result.myadd(a[0])
+    result.myadd(a[1])
+  for x in items(a):
+    # works:
+    #result.sons.add(x)
+    # fails:
+    result.myadd x
+  if result.len == 1:
+    result = result.sons[0] # this must not move!
+
+when true:
+  # bug #12957
+
+  proc p =
+    echo "A"
+    let x = sequence([charSet({'a'..'z', 'A'..'Z', '_'}),
+              charSet({'a'..'z', 'A'..'Z', '0'..'9', '_'})])
+    echo "B"
+  p()
+
+  proc testSubObjAssignment =
+    echo "begin"
+    # There must be extactly one element in the array constructor!
+    let x = sequence([charSet({'a'..'z', 'A'..'Z', '_'})])
+    echo "end"
+  testSubObjAssignment()
+
+
+#------------------------------------------------
+
+type
+  MyObject = object
+    x1: string
+    case kind1: bool
+      of false: y1: string
+      of true:
+          y2: seq[string]
+          case kind2: bool
+              of true: z1: string
+              of false:
+                z2: seq[string]
+                flag: bool
+    x2: string
+
+proc test_myobject =
+  var x: MyObject
+  x.x1 = "x1"
+  x.x2 = "x2"
+  x.y1 = "ljhkjhkjh"
+  x.kind1 = true
+  x.y2 = @["1", "2"]
+  x.kind2 = true
+  x.z1 = "yes"
+  x.kind2 = false
+  x.z2 = @["1", "2"]
+  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
+
+  try:
+    x.kind1 = x.flag # flag is not accesible
+  except FieldDefect:
+    echo "prevented"
+
+  doAssert(x.x1 == "x1")
+  doAssert(x.x2 == "x2")
+
+
+test_myobject()
+
+
+#------------------------------------------------
+# bug #14244
+
+type
+  RocksDBResult*[T] = object
+    case ok*: bool
+    of true:
+      value*: T
+    else:
+      error*: string
+
+proc init(): RocksDBResult[string] =
+  result.ok = true
+  result.value = "ok"
+
+echo init()
+
+
+#------------------------------------------------
+# bug #14312
+
+type MyObj = object
+  case kind: bool
+    of false: x0: int # would work with a type like seq[int]; value would be reset
+    of true: x1: string
+
+var a = MyObj(kind: false, x0: 1234)
+a.kind = true
+doAssert(a.x1 == "")
+
+block:
+  # bug #15532
+  type Kind = enum
+    k0, k1
+
+  type Foo = object
+    y: int
+    case kind: Kind
+    of k0: x0: int
+    of k1: x1: int
+
+  const j0 = Foo(y: 1, kind: k0, x0: 2)
+  const j1 = Foo(y: 1, kind: k1, x1: 2)
+
+  doAssert j0.y == 1
+  doAssert j0.kind == k0
+  doAssert j1.kind == k1
+
+  doAssert j1.x1 == 2
+  doAssert j0.x0 == 2