Merge pull request RustPython#3313 from DimitrisJim/mapping_check

Check if subscript is present for PyMapping::check.

Author: youknowone

vm/src/builtins/mappingproxy.rs

@@ -37,7 +37,7 @@ impl Constructor for PyMappingProxy {
     type Args = PyObjectRef;
 
     fn py_new(cls: PyTypeRef, mapping: Self::Args, vm: &VirtualMachine) -> PyResult {
-        if !PyMapping::check(&mapping)
+        if !PyMapping::check(&mapping, vm)
             || mapping.payload_if_subclass::<PyList>(vm).is_some()
             || mapping.payload_if_subclass::<PyTuple>(vm).is_some()
         {

vm/src/protocol/mapping.rs

@@ -26,10 +26,11 @@ where
     T: Borrow<PyObjectRef>;
 
 impl PyMapping<PyObjectRef> {
-    pub fn check(obj: &PyObjectRef) -> bool {
+    pub fn check(obj: &PyObjectRef, vm: &VirtualMachine) -> bool {
         obj.class()
             .mro_find_map(|x| x.slots.as_mapping.load())
-            .is_some()
+            .map(|f| f(obj, vm).subscript.is_some())
+            .unwrap_or(false)
     }
 
     pub fn methods(&self, vm: &VirtualMachine) -> PyMappingMethods {
@@ -119,7 +120,7 @@ impl IntoPyObject for PyMapping<PyObjectRef> {
 
 impl TryFromObject for PyMapping<PyObjectRef> {
     fn try_from_object(vm: &VirtualMachine, mapping: PyObjectRef) -> PyResult<Self> {
-        if Self::check(&mapping) {
+        if Self::check(&mapping, vm) {
             Ok(Self::new(mapping))
         } else {
             Err(vm.new_type_error(format!("{} is not a mapping object", mapping.class())))