Python: Remove some simple uses of points-to

python/ql/lib/semmle/python/dataflow/new/internal/Builtins.qll

@@ -32,7 +32,9 @@ module Builtins {
         "UnicodeDecodeError", "UnicodeEncodeError", "UnicodeError", "UnicodeTranslateError",
         "UnicodeWarning", "UserWarning", "ValueError", "Warning", "ZeroDivisionError",
         // Added for compatibility
-        "exec"
+        "exec",
+        // Added by the `site` module (available by default unless `-S` is used)
+        "copyright", "credits", "exit", "quit"
       ]
     or
     // Built-in constants shared between Python 2 and 3
@@ -51,8 +53,8 @@ module Builtins {
     or
     // Python 2 only
     result in [
-        "basestring", "cmp", "execfile", "file", "long", "raw_input", "reduce", "reload", "unichr",
-        "unicode", "xrange"
+        "apply", "basestring", "cmp", "execfile", "file", "long", "raw_input", "reduce", "reload",
+        "unichr", "unicode", "xrange"
       ]
   }
 

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll

@@ -1956,3 +1956,161 @@ private module OutNodes {
  * `kind`.
  */
 OutNode getAnOutNode(DataFlowCall call, ReturnKind kind) { call = result.getCall(kind) }
+
+/**
+ * Provides predicates for approximating type properties of user-defined classes
+ * based on their structure (method declarations, base classes).
+ *
+ * This module should _not_ be used in the call graph computation itself, as parts of it may depend
+ * on layers that themselves build upon the call graph (e.g. API graphs).
+ */
+module DuckTyping {
+  private import semmle.python.ApiGraphs
+
+  /**
+   * Holds if `cls` or any of its resolved superclasses declares a method with the given `name`.
+   */
+  predicate hasMethod(Class cls, string name) {
+    cls.getAMethod().getName() = name
+    or
+    hasMethod(getADirectSuperclass(cls), name)
+  }
+
+  /**
+   * Holds if `cls` has a base class that cannot be resolved to a user-defined class
+   * and is not just `object`, meaning it may inherit methods from an unknown class.
+   */
+  predicate hasUnresolvedBase(Class cls) {
+    exists(Expr base | base = cls.getABase() |
+      not base = classTracker(_).asExpr() and
+      not base = API::builtin("object").getAValueReachableFromSource().asExpr()
+    )
+  }
+
+  /**
+   * Holds if `cls` supports the container protocol, i.e. it declares
+   * `__contains__`, `__iter__`, or `__getitem__`.
+   */
+  predicate isContainer(Class cls) {
+    hasMethod(cls, "__contains__") or
+    hasMethod(cls, "__iter__") or
+    hasMethod(cls, "__getitem__")
+  }
+
+  /**
+   * Holds if `cls` supports the iterable protocol, i.e. it declares
+   * `__iter__` or `__getitem__`.
+   */
+  predicate isIterable(Class cls) {
+    hasMethod(cls, "__iter__") or
+    hasMethod(cls, "__getitem__")
+  }
+
+  /**
+   * Holds if `cls` supports the iterator protocol, i.e. it declares
+   * both `__iter__` and `__next__`.
+   */
+  predicate isIterator(Class cls) {
+    hasMethod(cls, "__iter__") and
+    hasMethod(cls, "__next__")
+  }
+
+  /**
+   * Holds if `cls` supports the context manager protocol, i.e. it declares
+   * both `__enter__` and `__exit__`.
+   */
+  predicate isContextManager(Class cls) {
+    hasMethod(cls, "__enter__") and
+    hasMethod(cls, "__exit__")
+  }
+
+  /**
+   * Holds if `cls` supports the descriptor protocol, i.e. it declares
+   * `__get__`, `__set__`, or `__delete__`.
+   */
+  predicate isDescriptor(Class cls) {
+    hasMethod(cls, "__get__") or
+    hasMethod(cls, "__set__") or
+    hasMethod(cls, "__delete__")
+  }
+
+  /**
+   * Holds if `cls` directly assigns to an attribute named `name` in its class body.
+   * This covers attribute assignments like `x = value`, but not method definitions.
+   */
+  predicate declaresAttribute(Class cls, string name) { exists(getAnAttributeValue(cls, name)) }
+
+  /**
+   * Gets the value expression assigned to attribute `name` directly in the class body of `cls`.
+   */
+  Expr getAnAttributeValue(Class cls, string name) {
+    exists(Assign a |
+      a.getScope() = cls and
+      a.getATarget().(Name).getId() = name and
+      result = a.getValue()
+    )
+  }
+
+  /**
+   * Holds if `cls` is callable, i.e. it declares `__call__`.
+   */
+  predicate isCallable(Class cls) { hasMethod(cls, "__call__") }
+
+  /**
+   * Holds if `cls` supports the mapping protocol, i.e. it declares
+   * `__getitem__` and `__keys__`, or `__getitem__` and `__iter__`.
+   */
+  predicate isMapping(Class cls) {
+    hasMethod(cls, "__getitem__") and
+    (hasMethod(cls, "keys") or hasMethod(cls, "__iter__"))
+  }
+
+  /**
+   * Holds if `cls` is a new-style class. In Python 3, all classes are new-style.
+   * In Python 2, a class is new-style if it (transitively) inherits from `object`,
+   * or has a declared `__metaclass__`, or has an unresolved base class.
+   */
+  predicate isNewStyle(Class cls) {
+    major_version() = 3
+    or
+    major_version() = 2 and
+    (
+      cls.getABase() = API::builtin("object").getAValueReachableFromSource().asExpr()
+      or
+      isNewStyle(getADirectSuperclass(cls))
+      or
+      hasUnresolvedBase(cls)
+      or
+      exists(cls.getMetaClass())
+      or
+      // Module-level __metaclass__ = type makes all classes in the module new-style
+      exists(Assign a |
+        a.getScope() = cls.getEnclosingModule() and
+        a.getATarget().(Name).getId() = "__metaclass__"
+      )
+    )
+  }
+
+  /**
+   * Gets the `__init__` function that will be invoked when `cls` is constructed,
+   * resolved according to the MRO.
+   */
+  Function getInit(Class cls) { result = invokedFunctionFromClassConstruction(cls, "__init__") }
+
+  /**
+   * Holds if `f` overrides a method in a superclass with the same name.
+   */
+  predicate overridesMethod(Function f) {
+    exists(Class cls | f.getScope() = cls | hasMethod(getADirectSuperclass(cls), f.getName()))
+  }
+
+  /**
+   * Holds if `f` is a property accessor (decorated with `@property`, `@name.setter`,
+   * or `@name.deleter`).
+   */
+  predicate isPropertyAccessor(Function f) {
+    exists(Attribute a | a = f.getADecorator() | a.getName() = "setter" or a.getName() = "deleter")
+    or
+    f.getADecorator().(Name).getId() = "property"
+  }
+}

python/ql/src/Classes/InconsistentMRO.ql

@@ -12,19 +12,24 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
-ClassObject left_base(ClassObject type, ClassObject base) {
-  exists(int i | i > 0 and type.getBaseType(i) = base and result = type.getBaseType(i - 1))
+/**
+ * Gets the `i`th base class of `cls`, if it can be resolved to a user-defined class.
+ */
+Class getBaseType(Class cls, int i) { cls.getBase(i) = classTracker(result).asExpr() }
+
+Class left_base(Class type, Class base) {
+  exists(int i | i > 0 and getBaseType(type, i) = base and result = getBaseType(type, i - 1))
 }
 
-predicate invalid_mro(ClassObject t, ClassObject left, ClassObject right) {
-  t.isNewStyle() and
+predicate invalid_mro(Class t, Class left, Class right) {
+  DuckTyping::isNewStyle(t) and
   left = left_base(t, right) and
-  left = right.getAnImproperSuperType()
+  left = getADirectSuperclass*(right)
 }
 
-from ClassObject t, ClassObject left, ClassObject right
+from Class t, Class left, Class right
 where invalid_mro(t, left, right)
 select t,
   "Construction of class " + t.getName() +

python/ql/src/Classes/PropertyInOldStyleClass.ql

@@ -11,10 +11,13 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
-from PropertyObject prop, ClassObject cls
-where cls.declaredAttribute(_) = prop and not cls.failedInference() and not cls.isNewStyle()
+from Function prop, Class cls
+where
+  prop.getScope() = cls and
+  prop.getADecorator().(Name).getId() = "property" and
+  not DuckTyping::isNewStyle(cls)
 select prop,
   "Property " + prop.getName() + " will not work properly, as class " + cls.getName() +
     " is an old-style class."

python/ql/src/Classes/ShouldBeContextManager.ql

@@ -14,10 +14,12 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
-from ClassValue c
-where not c.isBuiltin() and not c.isContextManager() and exists(c.declaredAttribute("__del__"))
+from Class c
+where
+  not DuckTyping::isContextManager(c) and
+  DuckTyping::hasMethod(c, "__del__")
 select c,
   "Class " + c.getName() +
     " implements __del__ (presumably to release some resource). Consider making it a context manager."

python/ql/src/Classes/SlotsInOldStyleClass.ql

@@ -12,9 +12,11 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
-from ClassObject c
-where not c.isNewStyle() and c.declaresAttribute("__slots__") and not c.failedInference()
+from Class c
+where
+  not DuckTyping::isNewStyle(c) and
+  DuckTyping::declaresAttribute(c, "__slots__")
 select c,
   "Using '__slots__' in an old style class just creates a class attribute called '__slots__'."

python/ql/src/Classes/SuperInOldStyleClass.ql

@@ -11,14 +11,13 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
 predicate uses_of_super_in_old_style_class(Call s) {
-  exists(Function f, ClassObject c |
+  exists(Function f, Class c |
     s.getScope() = f and
-    f.getScope() = c.getPyClass() and
-    not c.failedInference() and
-    not c.isNewStyle() and
+    f.getScope() = c and
+    not DuckTyping::isNewStyle(c) and
     s.getFunc().(Name).getId() = "super"
   )
 }

python/ql/src/Classes/UselessClass.ql

@@ -13,7 +13,7 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
 predicate fewer_than_two_public_methods(Class cls, int methods) {
   (methods = 0 or methods = 1) and
@@ -25,13 +25,8 @@ predicate does_not_define_special_method(Class cls) {
 }
 
 predicate no_inheritance(Class c) {
-  not exists(ClassValue cls, ClassValue other |
-    cls.getScope() = c and
-    other != ClassValue::object()
-  |
-    other.getABaseType() = cls or
-    cls.getABaseType() = other
-  ) and
+  not exists(getADirectSubclass(c)) and
+  not exists(getADirectSuperclass(c)) and
   not exists(Expr base | base = c.getABase() |
     not base instanceof Name or base.(Name).getId() != "object"
   )

python/ql/src/Classes/WrongNameForArgumentInClassInstantiation.ql

@@ -15,12 +15,34 @@
  */
 
 import python
-import Expressions.CallArgs
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
-from Call call, ClassValue cls, string name, FunctionValue init
+/**
+ * Holds if `name` is a legal argument name for calling `init`.
+ */
+bindingset[name]
+predicate isLegalArgumentName(Function init, string name) {
+  exists(init.getArgByName(name))
+  or
+  init.hasKwArg()
+}
+
+/**
+ * Holds if `call` constructs class `cls` and passes a keyword argument `name`
+ * that does not correspond to any parameter of `cls.__init__`.
+ */
+predicate illegally_named_parameter(Call call, Class cls, string name) {
+  exists(Function init |
+    resolveClassCall(call.getAFlowNode(), cls) and
+    init = DuckTyping::getInit(cls) and
+    name = call.getANamedArgumentName() and
+    not isLegalArgumentName(init, name)
+  )
+}
+
+from Call call, Class cls, string name, Function init
 where
   illegally_named_parameter(call, cls, name) and
-  init = get_function_or_initializer(cls)
+  init = DuckTyping::getInit(cls)
 select call, "Keyword argument '" + name + "' is not a supported parameter name of $@.", init,
   init.getQualifiedName()