Incorrect code generated for tagged unions with enums not starting at zero

[zielmicha]

type DbusTypeChar* = enum
  dtArray = 'a',
  dtDict = '{'

type DbusFoobar = ref object
  case kind: DbusTypeChar:
  of dtDict:
    foo: int
  else:
    bar: int

var foobar: DbusFoobar
foobar.kind = dtDict

In this example, DbusTypeChar is non-ordinal, but the compiler generates incorrect code even when dtDict = 'b'.
Generated C code:
https://gist.github.com/zielmicha/9a72ab049820a154d4e3
NimDT is declared as having 28 elements ('{' - 'a' == 26):

TNimNode* NimDT_91012_kind[28];

And the compiler generates out of bounds accesses ('{' == 123)

NimDT_91012_kind[123] = &TMP137[4];

[ziotom78]

With this change, the following code (scrapped from a project of mine) does no longer compile:

type
    DataType* {. pure .} = enum
        Char = 1, 
        Int8 = 2,
        Int16 = 3, 
        Int32 = 4, 
        Int64 = 5, 
        Float32 = 6, 
        Float64 = 7

    DataSeq* {. pure .} = object
        case kind* : DataType
        of DataType.Char: charSeq* : seq[char]
        of DataType.Int8: int8Seq* : seq[int8]
        of DataType.Int16: int16Seq* : seq[int16]
        of DataType.Int32: int32Seq* : seq[int32]
        of DataType.Int64: int64Seq* : seq[int64]
        of DataType.Float32: float32Seq* : seq[float32]
        of DataType.Float64: float64Seq* : seq[float64]

        length* : int

It fails with the message:

test.nim(12, 9) Error: low(kind) must be 0 for discriminant

Is this intentional? I would prefer not to change the values in the DataType enum, as they match the numbers expected in a byte stream read by the program.

[Araq]

Well yes it is intentional, it never worked reliably in the first place. Please use instead:

DataType* {. pure .} = enum
        None = 0,
        Char = 1, 
        Int8 = 2, ...