Bind wasmtime_trap_exit_status

* Add an `ExitTrap` subclass of `Trap`
* Return an appropriate trap from `Trap.__from_ptr__`
* Attach the exit code via a `code` field

Closes bytecodealliance#30

tests/test_trap.py

@@ -78,3 +78,32 @@ def test_frames_no_module(self):
         self.assertEqual(frames[0].func_index, 0)
         self.assertEqual(frames[0].func_name, None)
         self.assertEqual(frames[0].module_name, None)
+
+    def test_wasi_exit(self):
+        store = Store()
+        module = Module(store, """
+            (module
+                (import "wasi_snapshot_preview1" "proc_exit" (func $exit (param i32)))
+                (func (export "exit") (param i32)
+                    local.get 0
+                    call $exit)
+            )
+        """)
+        linker = Linker(store)
+        wasi = WasiConfig()
+        linker.define_wasi(WasiInstance(store, "wasi_snapshot_preview1", wasi))
+        instance = linker.instantiate(module)
+        exit = instance.exports["exit"]
+        assert(isinstance(exit, Func))
+
+        try:
+            exit(0)
+            assert(False)
+        except ExitTrap as e:
+            assert(e.code == 0)
+
+        try:
+            exit(1)
+            assert(False)
+        except ExitTrap as e:
+            assert(e.code == 1)

wasmtime/__init__.py

@@ -22,7 +22,7 @@
 from ._wat2wasm import wat2wasm
 from ._module import Module
 from ._value import Val, IntoVal
-from ._trap import Trap, Frame
+from ._trap import Trap, Frame, ExitTrap
 from ._func import Func, Caller
 from ._globals import Global
 from ._table import Table
@@ -52,6 +52,7 @@
     'Memory',
     'Global',
     'Trap',
+    'ExitTrap',
     'Frame',
     'Module',
     'Instance',

wasmtime/_bindings.py

@@ -1972,6 +1972,12 @@ def wasmtime_interrupt_handle_new(store: Any) -> pointer:
 def wasmtime_interrupt_handle_interrupt(handle: Any) -> None:
     return _wasmtime_interrupt_handle_interrupt(handle)  # type: ignore
 
+_wasmtime_trap_exit_status = dll.wasmtime_trap_exit_status
+_wasmtime_trap_exit_status.restype = c_bool
+_wasmtime_trap_exit_status.argtypes = [POINTER(wasm_trap_t), POINTER(c_int)]
+def wasmtime_trap_exit_status(arg0: Any, status: Any) -> c_bool:
+    return _wasmtime_trap_exit_status(arg0, status)  # type: ignore
+
 _wasmtime_frame_func_name = dll.wasmtime_frame_func_name
 _wasmtime_frame_func_name.restype = POINTER(wasm_name_t)
 _wasmtime_frame_func_name.argtypes = [POINTER(wasm_frame_t)]

wasmtime/_trap.py

@@ -1,5 +1,5 @@
 from . import _ffi as ffi
-from ctypes import byref, POINTER, pointer
+from ctypes import byref, POINTER, pointer, c_int
 from wasmtime import Store, WasmtimeError
 from typing import Optional, Any, List
 
@@ -24,9 +24,16 @@ def __init__(self, store: Store, message: str):
     def __from_ptr__(cls, ptr: "pointer[ffi.wasm_trap_t]") -> "Trap":
         if not isinstance(ptr, POINTER(ffi.wasm_trap_t)):
             raise TypeError("wrong pointer type")
-        trap: "Trap" = cls.__new__(cls)
-        trap.__ptr__ = ptr
-        return trap
+        exit_code = c_int(0)
+        if ffi.wasmtime_trap_exit_status(ptr, byref(exit_code)):
+            exit_trap: ExitTrap = ExitTrap.__new__(ExitTrap)
+            exit_trap.__ptr__ = ptr
+            exit_trap.code = exit_code.value
+            return exit_trap
+        else:
+            trap: Trap = cls.__new__(cls)
+            trap.__ptr__ = ptr
+            return trap
 
     @property
     def message(self) -> str:
@@ -60,6 +67,23 @@ def __del__(self) -> None:
             ffi.wasm_trap_delete(self.__ptr__)
 
 
+class ExitTrap(Trap):
+    """
+    A special type of `Trap` which represents the process exiting via WASI's
+    `proc_exit` function call.
+
+    Whenever a WASI program exits via `proc_exit` a trap is raised, but the
+    trap will have this type instead of `Trap`, so you can catch just this
+    type instead of all traps (if desired). Exit traps have a `code` associated
+    with them which is the exit code provided at exit.
+
+    Note that `ExitTrap` is a subclass of `Trap`, so if you catch a trap you'll
+    also catch `ExitTrap`.
+    """
+    code: int
+    pass
+
+
 class Frame:
     __ptr__: "pointer[ffi.wasm_frame_t]"
     __owner__: Optional[Any]