PY-24969 Don't keep PyAnnotationStubs for assignments and type declarations

Namely, retain them only for function return type annotations and
named parameters, since for these two PSI nodes we use
getStubOrPsiChild() in getAnnotation() as a way to quickly check
whether there is annotation at all. Otherwise, stubs for annotations
of local variables might be stored directly in a function stub and
thus falsely recognized as a type hint for its return value.

python/src/com/jetbrains/python/psi/PyFileElementType.java

@@ -62,7 +62,7 @@ public class PyFileElementType extends IStubFileElementType<PyFileStub> {
   @Override
   public int getStubVersion() {
     // Don't forget to update versions of indexes that use the updated stub-based elements
-    return 64;
+    return 65;
   }
 
   @Nullable

python/src/com/jetbrains/python/psi/impl/stubs/PyAnnotationElementType.java

@@ -24,7 +24,9 @@ import com.intellij.psi.PsiElement;
 import com.intellij.psi.stubs.StubElement;
 import com.intellij.psi.stubs.StubInputStream;
 import com.intellij.psi.stubs.StubOutputStream;
+import com.intellij.psi.tree.IElementType;
 import com.jetbrains.python.PyElementTypes;
+import com.jetbrains.python.PythonDialectsTokenSetProvider;
 import com.jetbrains.python.psi.PyAnnotation;
 import com.jetbrains.python.psi.PyStubElementType;
 import com.jetbrains.python.psi.impl.PyAnnotationImpl;
@@ -66,4 +68,11 @@ public class PyAnnotationElementType extends PyStubElementType<PyAnnotationStub,
       throws IOException {
     return new PyAnnotationStubImpl(parentStub, PyElementTypes.ANNOTATION);
   }
+
+  @Override
+  public boolean shouldCreateStub(ASTNode node) {
+    final IElementType parentType = node.getTreeParent().getElementType();
+    return PythonDialectsTokenSetProvider.INSTANCE.getFunctionDeclarationTokens().contains(parentType)
+           || PythonDialectsTokenSetProvider.INSTANCE.getParameterTokens().contains(parentType);
+  }
 }

python/testData/stubs/FunctionStubDoesNotContainLocalVariableAnnotation.py

@@ -0,0 +1,2 @@
+def func():
+    x: int = 42

python/testSrc/com/jetbrains/python/PyStubsTest.java

@@ -871,4 +871,14 @@ public class PyStubsTest extends PyTestCase {
       assertNotParsed(libFile);
     });
   }
+
+  // PY-24969
+  public void testFunctionStubDoesNotContainLocalVariableAnnotation() {
+    runWithLanguageLevel(LanguageLevel.PYTHON36, () -> {
+      final PyFile file = getTestFile();
+      final PyFunction func = file.findTopLevelFunction("func");
+      final PyFunctionStub funcStub = func.getStub();
+      assertNull(funcStub.findChildStubByType(PyElementTypes.ANNOTATION));
+    });
+  }
 }