Ensure executor attributes are defined by subclasses

dmoj/executors/compiled_executor.py

@@ -1,4 +1,3 @@
-import abc
 import hashlib
 import os
 import signal
@@ -10,6 +9,7 @@
 import pylru
 
 from dmoj.error import CompileError, OutputLimitExceeded
+from dmoj.executors.metaclass import ExecutorMeta
 from dmoj.judgeenv import env
 from dmoj.utils.communicate import safe_communicate
 from dmoj.utils.unicode import utf8bytes
@@ -26,7 +26,7 @@
 # Contract: if cached=True is specified and an entry exists in the cache,
 # `create_files` and `compile` will not be run, and `_executable` will be loaded
 # from the cache.
-class _CompiledExecutorMeta(abc.ABCMeta):
+class _CompiledExecutorMeta(ExecutorMeta):
     @staticmethod
     def _cleanup_cache_entry(_key, executor: object) -> None:
         # Mark the executor as not-cached, so that if this is the very last reference

dmoj/executors/metaclass.py

@@ -0,0 +1,20 @@
+import abc
+
+
+class ExecutorMeta(abc.ABCMeta):
+    """This metaclass treats class attributes that are annotated but never assigned as abstract.
+
+    For example:
+    >>> class Example(ExecutorMeta):
+    ...     x: int
+    would be an abstract class unless `x` is implemented.
+
+    This means that when instantiating, an exception will be raised:
+    >>> Example()
+    TypeError: Can't instantiate abstract class Example with abstract methods x
+    """
+
+    def __new__(mcs, *args, **kwargs):
+        cls = super().__new__(mcs, *args, **kwargs)
+        cls.__abstractmethods__ |= {a for a in getattr(cls, '__annotations__', {}).keys() if not hasattr(cls, a)}
+        return cls

dmoj/executors/mixins.py

@@ -1,4 +1,3 @@
-import abc
 import os
 import re
 import shutil
@@ -7,6 +6,7 @@
 from dmoj.cptbox import IsolateTracer, TracedPopen, syscalls
 from dmoj.cptbox.handlers import ALLOW
 from dmoj.error import InternalError
+from dmoj.executors.metaclass import ExecutorMeta
 from dmoj.judgeenv import env
 from dmoj.utils import setbufsize_path
 from dmoj.utils.unicode import utf8bytes
@@ -36,7 +36,7 @@
     BASE_FILESYSTEM += [r'/etc/ld\.so\.(?:nohwcap|preload|cache)$']
 
 
-class PlatformExecutorMixin(metaclass=abc.ABCMeta):
+class PlatformExecutorMixin(metaclass=ExecutorMeta):
     address_grace = 65536
     data_grace = 0
     fsize = 0