regression(1.2.6 => devel): VM: const case object field access gives: 'sons' is not accessible

[timotheecour]

regression(1.2.6 => devel): VM: const case object field access gives: 'sons' is not accessible

Example

block:
  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  # 1.2.6: works; devel: Error: unhandled exception: 'sons' is not accessible using discriminant 'kind' of type 'TNode' [FieldDefect]
  # echo j0.x0 # 1.2.6: prints 0 instead of 2 but; nim devel: CT error

Current Output

Error: unhandled exception: 'sons' is not accessible using discriminant 'kind' of type 'TNode'

Expected Output

works

Additional Information

• related to VM: const case object gets some fields zeroed out at runtime #13081 which was maybe accidentally fixed in a yet unknown commit (needs git biscect; this might shed light on this regression)
• devel 1.3.7 3eaacac
• showstopper tag debatable given that const case object field worked in 1.2.6 in a partial way (some software might have relied on the parts that did work and are now broken)
• a test case for this issue was added (commented out) in close #13081 #15529