multimethods: Error: internal error: cgmeth.genConv

[Parashurama]

the following code create a compiler error:

type
    BaseEvent* = object of RootObj
        data: pointer

    Control* = object of RootObj
        state: bool

    Button* = object of Control
        is_clicked : bool

    Dialog* = object of Control
        content: seq[RootObj]

method dummy_event*(self: Button, ev: BaseEvent) : bool {.base.} =
    discard

method dummy_event*(self: Dialog, ev: BaseEvent) : bool =
    discard

Error: internal error: cgmeth.genConv
No stack traceback available
To create a stacktrace, rerun compilation with ./koch temp c
main_module.nim(21, 21) Error: internal error: cgmeth.genConv
Traceback (most recent call last)
nim.nim(107) nim
nim.nim(71) handleCmdLine
main.nim(251) mainCommand
main.nim(63) commandCompileToC
modules.nim(221) compileProject
modules.nim(169) compileModule
passes.nim(206) processModule
passes.nim(129) closePasses
cgen.nim(1310) myClose
cgmeth.nim(259) generateMethodDispatchers
cgmeth.nim(231) genDispatcher
cgmeth.nim(21) genConv
msgs.nim(991) internalError
msgs.nim(965) liMessage
msgs.nim(837) handleError
msgs.nim(821) quit
FAILURE

VERSION:
Nim Compiler Version 0.12.1 (2015-11-15) [Linux: amd64]
Copyright (c) 2006-2015 by Andreas Rumpf

git hash: 0f7fdd8
active boot switches: -d:release

---

the problem disappear if BaseEvent changed to 'int' or another basic type but warn that second 'dummy_event' should have 'base' pragma.

Also the compiler doesn't accept 'base' pragma on second method if both arguments are objects

[Parashurama]

Following on this issue

It seems to me that the following should to be the solution since their common ancestor doesn't have 'dummy_method'. But this doesn't work either! error: main_module.nim(18, 8) Error: method is not a base

Is this another bug or something i missed?

type
    BaseEvent* = object of RootObj
        data:pointer

    Control* = object of RootObj
        state: bool

    Button* = object of Control
        is_clicked : bool

    Dialog* = object of Control
        content: seq[RootObj]

method dummy_event*(self: Button, ev: BaseEvent) : bool {.base.} =
    discard

method dummy_event*(self: Dialog, ev: BaseEvent) : bool {.base.} =
    discard

[Araq]

Whatever the compiler implements, it has to be consistent (right now it isn't) and in the spec.

[Parashurama]

So, how this problem could be solved? Any workaround?

[jangko]

type
  ByteArray* = ref object of RootObj
  OutputStream* = ref object of RootObj

method CopyTo*(ba, target: ByteArray): int = discard
method CopyTo*(ba: ByteArray, os: OutputStream): int = discard

this is perhaps related with the above issue
the above code produce error message:

bytearray.nim(5, 8) Warning: use {.base.} for base methods; baseless methods are
 deprecated [UseBase]
bytearray.nim(5, 20) Error: there is no subtype relation between OutputStream an
d ByteArray

ver 0.11.2: compile success
0.12.0: failed with ICE
0.12.1: failed with no subtype relation

if the target param removed(which is undesired), no error