Parse "foo, optional" as Union[foo, None] as a workaround for parameters with default values (PY-15298)

It results in false negatives for optional parameters with non-None
default values, but at least we don't need to switch from stubs to AST
in the type checker inspection for every function with optional
parameters.

python/src/com/jetbrains/numpy/codeInsight/NumpyDocStringTypeProvider.java

@@ -30,6 +30,7 @@ import com.jetbrains.python.documentation.PyDocumentationSettings;
 import com.jetbrains.python.psi.*;
 import com.jetbrains.python.psi.impl.PyBuiltinCache;
 import com.jetbrains.python.psi.impl.PyExpressionCodeFragmentImpl;
+import com.jetbrains.python.psi.types.PyNoneType;
 import com.jetbrains.python.psi.types.PyType;
 import com.jetbrains.python.psi.types.PyTypeProviderBase;
 import com.jetbrains.python.psi.types.TypeEvalContext;
@@ -244,8 +245,12 @@ public class NumpyDocStringTypeProvider extends PyTypeProviderBase {
 
   @Nullable
   private static PyType parseNumpyDocType(@NotNull PsiElement anchor, @NotNull String typeString) {
-    typeString = NumPyDocString.cleanupOptional(typeString);
+    final String withoutOptional = NumPyDocString.cleanupOptional(typeString);
     final Set<PyType> types = new LinkedHashSet<PyType>();
+    if (withoutOptional != null) {
+      typeString = withoutOptional;
+      types.add(PyNoneType.INSTANCE);
+    }
     for (String typeName : NumPyDocString.getNumpyUnionType(typeString)) {
       PyType parsedType = parseSingleNumpyDocType(anchor, typeName);
       if (parsedType != null) {

python/src/com/jetbrains/numpy/documentation/NumPyDocString.java

@@ -276,13 +276,13 @@ public class NumPyDocString {
     }
   }
 
-  @NotNull
+  @Nullable
   public static String cleanupOptional(@NotNull String typeString) {
     int index = typeString.indexOf(", optional");
     if (index >= 0) {
       return typeString.substring(0, index);
     }
-    return typeString;
+    return null;
   }
 
   @NotNull

python/testData/quickdoc/NumPyOnesDoc.html

@@ -1,2 +1,2 @@
 def ones(shape, dtype=None, order='C')
-Inferred type: (shape:&nbsp;Union[<a href="psi_element://#typename#int">int</a>,&nbsp;Iterable[<a href="psi_element://#typename#int">int</a>]],&nbsp;dtype:&nbsp;<a href="psi_element://#typename#object">object</a>,&nbsp;order:&nbsp;<a href="psi_element://#typename#str">str</a>)&nbsp;-&gt;&nbsp;ndarray<br>
+Inferred type: (shape:&nbsp;Union[<a href="psi_element://#typename#int">int</a>,&nbsp;Iterable[<a href="psi_element://#typename#int">int</a>]],&nbsp;dtype:&nbsp;Optional[<a href="psi_element://#typename#object">object</a>],&nbsp;order:&nbsp;Optional[<a href="psi_element://#typename#str">str</a>])&nbsp;-&gt;&nbsp;ndarray<br>