[Project] Antichecked Exceptions

An alternative to checked exceptions that actually catches bugs and
prevents unintended exceptions from being accidentally caught/silenced.
Made for Python.

5 files changed, 276 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
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+__pycache__/
diff --git a/LICENSE b/LICENSE
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+++ b/LICENSE
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+Copyright (c) 2021 Soni L.
+
+Permission is hereby granted, free of charge, to any person ("You") obtaining
+a copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation the
+rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+sell copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+This license shall be void if You bring a copyright lawsuit, related or
+unrelated to the Software, against any of the copyright holders.
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/antichecked.py b/antichecked.py
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+# Antichecked Exceptions for Python
+# Copyright (c) 2021 Soni L.
+#
+# Permission is hereby granted, free of charge, to any person ("You") obtaining
+# a copy of this software and associated documentation files (the "Software"),
+# to deal in the Software without restriction, including without limitation the
+# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+# sell copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# This license shall be void if You bring a copyright lawsuit, related or
+# unrelated to the Software, against any of the copyright holders.
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+"""Antichecked exceptions for Python.
+
+This package implements antichecked exceptions. They're analogous to the
+reverse of checked exceptions, that's why they're called antichecked.
+
+Just ``from antichecked import exceptions`` and you're ready to go!
+"""
+
+__version__ = '1.0'
+
+class _hack:
+    def __init__(self, ctx):
+        self.ctx = ctx
+
+    def __enter__(self):
+        pass
+
+    def __exit__(self, exc_ty, exc_val, exc_tb):
+        exc_val.__context__ = self.ctx
+
+class exceptions:
+    """A context manager for antichecked exceptions.
+
+    Antichecked exceptions are the reverse of checked exceptions: rather than
+    requiring the caller to catch the exceptions, they actively check that
+    your function/block actually intended to raise them.
+
+    Examples:
+
+        >>> from antichecked import exceptions
+
+        Intercepting exceptions::
+
+        >>> with exceptions(StopIteration) as r:
+        ...     raise StopIteration
+            RuntimeError
+
+        Raising exceptions::
+
+        >>> with exceptions(StopIteration) as r:
+        ...     raise r(StopIteration)
+            StopIteration
+
+        Adding a cause::
+
+        >>> with exceptions(StopIteration) as r:
+        ...     raise r(StopIteration) from ValueError()
+            StopIteration from ValueError
+
+        Similarly, re-raising exceptions is done with ``raise r``.
+    """
+
+    def __init__(self, *args):
+        """Creates an antichecked exception context for the given exceptions.
+
+        Args:
+            Accepts an arbitrary amount of exception types.
+        """
+        # each context manager gets an unique exception type
+        class WrappedError(Exception):
+            def __init__(self, exc=None):
+                if isinstance(exc, BaseException) or exc is None:
+                    self.value = exc
+                else:
+                    self.value = exc()
+        self._exceptions = args
+        self._error = WrappedError
+
+    def __enter__(self):
+        return self._error
+
+    def __exit__(self, exc_ty, exc_val, exc_tb):
+        if exc_ty is None:
+            return
+        if exc_ty is self._error:
+            # handle `raise r(exc)` similar to `raise exc`
+            if exc_val.value is not None:
+                exc = exc_val.value
+                exc.__cause__ = exc_val.__cause__
+                exc.__suppress_context__ = exc_val.__suppress_context__
+                with _hack(exc_val.__context__):
+                    raise exc.with_traceback(exc_tb)
+            # `raise r from foo` is unhandled, as `raise from foo` is not
+            # valid python. TODO make this case a RuntimeError.
+            pass
+            # handle `raise r` similar to `raise`
+            if exc_val.__context__ is None:
+                with _hack(None):
+                    exc = RuntimeError("No active exception to re-raise")
+                    raise exc.with_traceback(exc_tb)
+            with _hack(exc_val.__context__.__context__):
+                raise exc_val.__context__
+        if any(issubclass(exc_ty, e) for e in self._exceptions):
+            # handle this similar to StopIteration in generators
+            raise RuntimeError("Antichecked exception raised") from exc_val
diff --git a/pyproject.toml b/pyproject.toml
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+[build-system]
+requires = ["flit_core >=3.2,<4"]
+build-backend = "flit_core.buildapi"
+
+[project]
+name = "antichecked"
+authors = [{name = "SoniEx2", email = "endermoneymod@gmail.com"}]
+dynamic = ["version", "description"]
diff --git a/test.py b/test.py
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+++ b/test.py
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+# Unit tests for Antichecked Exceptions for Python
+# Copyright (c) 2021 Soni L.
+#
+# Permission is hereby granted, free of charge, to any person ("You") obtaining
+# a copy of this software and associated documentation files (the "Software"),
+# to deal in the Software without restriction, including without limitation the
+# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+# sell copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# This license shall be void if You bring a copyright lawsuit, related or
+# unrelated to the Software, against any of the copyright holders.
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+from antichecked import exceptions
+
+class expect:
+    def __init__(self, exc, *, cause, context):
+        self.exc = exc
+        self.cause = cause or type(None)
+        self.context = context or type(None)
+
+    def __enter__(self):
+        pass
+
+    def __exit__(self, exc_ty, exc_val, exc_tb):
+        assert exc_ty is self.exc
+        assert type(exc_val.__cause__) is self.cause
+        assert type(exc_val.__context__) is self.context
+        return True
+
+def foo(i):
+    with exceptions(ValueError) as r:
+        try:
+            x = int(i)
+        except ValueError:
+            # re-raise ValueError from int()
+            raise r
+        else:
+            if x < 0:
+                # attempt to raise r without a context
+                # (should turn into RuntimeError, just like bare raise)
+                raise r
+            # this raises ValueError if x is not 1, and it becomes wrapped in
+            # RuntimeError
+            x, = [x]*x
+
+def test_foo():
+    # ValueError from int() passes through (re-raised), context/cause is None
+    with expect(ValueError, cause=None, context=None):
+        foo("false")
+    # ValueError from unpacking gets wrapped, cause and context are ValueError
+    with expect(RuntimeError, cause=ValueError, context=ValueError):
+        foo("10")
+    # raise r without context becomes RuntimeError
+    with expect(RuntimeError, cause=None, context=None):
+        foo("-10")
+    # "1" gets accepted and doesn't raise anything
+    foo("1")
+
+def bar():
+    with exceptions(ValueError) as r:
+        raise r
+
+def test_bar():
+    with expect(RuntimeError, cause=None, context=None):
+        bar()
+
+def fake_gen():
+    with exceptions(StopIteration) as r:
+        next(iter([]))
+
+def test_fake_gen():
+    # actual generators don't use RuntimeError but we have no way of testing that
+    with expect(RuntimeError, cause=StopIteration, context=StopIteration):
+        fake_gen()
+
+def baz(i):
+    with exceptions(ValueError) as r:
+        try:
+            x = int(i)
+        except ValueError:
+            # raise new exception with context
+            raise r(TypeError)
+        else:
+            if x < 0:
+                # raise a new ValueError
+                raise r(ValueError)
+            try:
+                x, = [x]*x
+            except ValueError as e:
+                # raise with cause
+                raise r(TypeError) from e
+
+def test_baz():
+    # ValueError from int() becomes TypeError with context
+    with expect(TypeError, cause=None, context=ValueError):
+        baz("false")
+    # raise TypeError with cause and context being ValueError
+    with expect(TypeError, cause=ValueError, context=ValueError):
+        baz("10")
+    # raise ValueError through antichecked exceptions
+    with expect(ValueError, cause=None, context=None):
+        baz("-10")
+    # "1" gets accepted and doesn't raise anything
+    baz("1")
+
+
+def test_all():
+    test_foo()
+    test_bar()
+    test_fake_gen()
+    test_baz()
+
+if __name__ == "__main__":
+    test_all()