Python: Add test for overloaded __init__ resolution

Adds a test showing that `@typing.overload` stubs are spuriously
resolved as call targets alongside the actual `__init__` implementation.

Author: tausbn

python/ql/test/library-tests/dataflow/calls-overload/OverloadCallTest.expected

@@ -0,0 +1,26 @@
+/**
+ * Test that `@typing.overload` stubs are not resolved as call targets.
+ */
+
+import python
+import semmle.python.dataflow.new.internal.DataFlowDispatch as DataFlowDispatch
+import utils.test.InlineExpectationsTest
+
+module OverloadCallTest implements TestSig {
+  string getARelevantTag() { result = "init" }
+
+  predicate hasActualResult(Location location, string element, string tag, string value) {
+    exists(location.getFile().getRelativePath()) and
+    exists(DataFlowDispatch::DataFlowCall call, Function target, DataFlowDispatch::CallType type |
+      location = call.getLocation() and
+      element = call.toString() and
+      DataFlowDispatch::resolveCall(call.getNode(), target, type) and
+      target.getName() = "__init__"
+    |
+      value = target.getQualifiedName() + ":" + target.getLocation().getStartLine().toString() and
+      tag = "init"
+    )
+  }
+}
+
+import MakeTest<OverloadCallTest>

python/ql/test/library-tests/dataflow/calls-overload/OverloadCallTest.ql

@@ -0,0 +1,39 @@
+import typing
+
+
+class OverloadedInit:
+    @typing.overload
+    def __init__(self, x: int) -> None: ...
+
+    @typing.overload
+    def __init__(self, x: str, y: str) -> None: ...
+
+    def __init__(self, x, y=None):
+        pass
+
+OverloadedInit(1) # $ init=OverloadedInit.__init__:11 SPURIOUS: init=OverloadedInit.__init__:6 init=OverloadedInit.__init__:9
+OverloadedInit("a", "b") # $ init=OverloadedInit.__init__:11 SPURIOUS: init=OverloadedInit.__init__:6 init=OverloadedInit.__init__:9
+
+
+from typing import overload
+
+
+class OverloadedInitFromImport:
+    @overload
+    def __init__(self, x: int) -> None: ...
+
+    @overload
+    def __init__(self, x: str, y: str) -> None: ...
+
+    def __init__(self, x, y=None):
+        pass
+
+OverloadedInitFromImport(1) # $ init=OverloadedInitFromImport.__init__:28 SPURIOUS: init=OverloadedInitFromImport.__init__:23 init=OverloadedInitFromImport.__init__:26
+OverloadedInitFromImport("a", "b") # $ init=OverloadedInitFromImport.__init__:28 SPURIOUS: init=OverloadedInitFromImport.__init__:23 init=OverloadedInitFromImport.__init__:26
+
+
+class NoOverloads:
+    def __init__(self, x):
+        pass
+
+NoOverloads(1) # $ init=NoOverloads.__init__:36