1 files changed, 117 insertions, 0 deletions
diff --git a/Tools/c-analyzer/c_common/clsutil.py b/Tools/c-analyzer/c_common/clsutil.py
new file mode 100644
index 0000000..aa5f6b9
--- /dev/null
+++ b/Tools/c-analyzer/c_common/clsutil.py
@@ -0,0 +1,117 @@
+
+_NOT_SET = object()
+
+
+class Slot:
+    """A descriptor that provides a slot.
+
+    This is useful for types that can't have slots via __slots__,
+    e.g. tuple subclasses.
+    """
+
+    __slots__ = ('initial', 'default', 'readonly', 'instances', 'name')
+
+    def __init__(self, initial=_NOT_SET, *,
+                 default=_NOT_SET,
+                 readonly=False,
+                 ):
+        self.initial = initial
+        self.default = default
+        self.readonly = readonly
+
+        # The instance cache is not inherently tied to the normal
+        # lifetime of the instances.  So must do something in order to
+        # avoid keeping the instances alive by holding a reference here.
+        # Ideally we would use weakref.WeakValueDictionary to do this.
+        # However, most builtin types do not support weakrefs.  So
+        # instead we monkey-patch __del__ on the attached class to clear
+        # the instance.
+        self.instances = {}
+        self.name = None
+
+    def __set_name__(self, cls, name):
+        if self.name is not None:
+            raise TypeError('already used')
+        self.name = name
+        try:
+            slotnames = cls.__slot_names__
+        except AttributeError:
+            slotnames = cls.__slot_names__ = []
+        slotnames.append(name)
+        self._ensure___del__(cls, slotnames)
+
+    def __get__(self, obj, cls):
+        if obj is None:  # called on the class
+            return self
+        try:
+            value = self.instances[id(obj)]
+        except KeyError:
+            if self.initial is _NOT_SET:
+                value = self.default
+            else:
+                value = self.initial
+            self.instances[id(obj)] = value
+        if value is _NOT_SET:
+            raise AttributeError(self.name)
+        # XXX Optionally make a copy?
+        return value
+
+    def __set__(self, obj, value):
+        if self.readonly:
+            raise AttributeError(f'{self.name} is readonly')
+        # XXX Optionally coerce?
+        self.instances[id(obj)] = value
+
+    def __delete__(self, obj):
+        if self.readonly:
+            raise AttributeError(f'{self.name} is readonly')
+        self.instances[id(obj)] = self.default  # XXX refleak?
+
+    def _ensure___del__(self, cls, slotnames):  # See the comment in __init__().
+        try:
+            old___del__ = cls.__del__
+        except AttributeError:
+            old___del__ = (lambda s: None)
+        else:
+            if getattr(old___del__, '_slotted', False):
+                return
+
+        def __del__(_self):
+            for name in slotnames:
+                delattr(_self, name)
+            old___del__(_self)
+        __del__._slotted = True
+        cls.__del__ = __del__
+
+    def set(self, obj, value):
+        """Update the cached value for an object.
+
+        This works even if the descriptor is read-only.  This is
+        particularly useful when initializing the object (e.g. in
+        its __new__ or __init__).
+        """
+        self.instances[id(obj)] = value
+
+
+class classonly:
+    """A non-data descriptor that makes a value only visible on the class.
+
+    This is like the "classmethod" builtin, but does not show up on
+    instances of the class.  It may be used as a decorator.
+    """
+
+    def __init__(self, value):
+        self.value = value
+        self.getter = classmethod(value).__get__
+        self.name = None
+
+    def __set_name__(self, cls, name):
+        if self.name is not None:
+            raise TypeError('already used')
+        self.name = name
+
+    def __get__(self, obj, cls):
+        if obj is not None:
+            raise AttributeError(self.name)
+        # called on the class
+        return self.getter(None, cls)