Callback crashes in emulation mode

[emoise-gsi]

callback_bug.zip
no_bug.zip

lpython version 0.18.4

Both callback_bug and no_bug (attached) contain three similar files:

• main.py, which drives the program
• emulation.py which contains the emulation implementation
• the_callback.py / some_func.py

We can run both programs in emulation mode, taking care to update the PYTHONPATH with the location of lpython.py:
$ PYTHONPATH=/home/emoise/lpython/src/runtime/lpython/ python main.py

no_bug works just fine:
3

the_callback fails:
Traceback (most recent call last):
File "/home/emoise/lpython/callback_bug/main.py", line 8, in
from the_callback import entry_point
File "/home/emoise/lpython/callback_bug/the_callback.py", line 8, in
def bar(func : Callable[[i32], i32], arg : i32) -> i32:
File "/home/emoise/lpython/src/runtime/lpython/lpython.py", line 471, in ccall
return CTypes(f)
File "/home/emoise/lpython/src/runtime/lpython/lpython.py", line 371, in init
arg_ctype = convert_type_to_ctype(arg_type)
File "/home/emoise/lpython/src/runtime/lpython/lpython.py", line 294, in convert_type_to_ctype
type = convert_type_to_ctype(arg._type)
File "/home/emoise/lpython/src/runtime/lpython/lpython.py", line 298, in convert_type_to_ctype
elif issubclass(arg, Enum):
TypeError: issubclass() arg 1 must be a class

[ubaidsk]

Sharing the contents of the zip files for easy reference.

no_bug.zip contents:

no_bug $ ls         
emulation.py    main.py         some_func.py

no_bug $ cat main.py 
import lpython
from types import FunctionType
import emulation

lpython.CTypes.emulations = {k: v for k, v in emulation.__dict__.items()
        if isinstance(v, FunctionType)}

from some_func import entry_point

entry_point()

no_bug $ cat emulation.py 
from lpython import i32

def bar(arg : i32) -> i32:
    print(arg)

no_bug $ cat some_func.py 
from lpython import ccallback, i32, ccall

@ccall
def bar(arg : i32) -> i32:
    pass

@ccallback
def entry_point() -> None:
    bar(3)

---

callback_bug.zip contents:

callback_bug $ ls
__pycache__     emulation.py    main.py         the_callback.py

callback_bug $ cat main.py 
import lpython
from types import FunctionType
import emulation

lpython.CTypes.emulations = {k: v for k, v in emulation.__dict__.items()
        if isinstance(v, FunctionType)}

from the_callback import entry_point

entry_point()

callback_bug $ cat emulation.py 
from lpython import i32, Callable

def bar(func : Callable[[i32], i32], arg : i32) -> i32:
    return func(arg)

callback_bug $ cat the_callback.py 
from lpython import ccallback, i32, Callable, ccall

def foo(x : i32) -> i32:
    print(x)
    return x

@ccall
def bar(func : Callable[[i32], i32], arg : i32) -> i32:
    pass

@ccallback
def entry_point() -> None:
    bar(foo, 3)

[Smit-create]

The following diff should fix that:

diff --git a/src/runtime/lpython/lpython.py b/src/runtime/lpython/lpython.py
index 4ec0faad4..eb48a8767 100644
--- a/src/runtime/lpython/lpython.py
+++ b/src/runtime/lpython/lpython.py
@@ -286,6 +286,8 @@ def convert_type_to_ctype(arg):
         return c_double_complex
     elif arg == bool:
         return ctypes.c_bool
+    elif arg == Callable:
+        return ctypes.PYFUNCTYPE(None)
     elif arg is None:
         raise NotImplementedError("Type cannot be None")
     elif isinstance(arg, Array):