seq: add __index__ op overriding class support

This commit fix three test cases in test_index.py
* SeqTestCase.test_index
* SeqTestCase.test_wrappers
* ListTestCase.test_setdelitem

All these three cases' failures were caused by not supporting classes
that override __index__ operator when indexing sequence type.

This commit implement almost same routine with PR(#2807) which also did not
support classes which override __index__ operator in range indexing.

Signed-off-by: snowapril <sinjihng@gmail.com>

Lib/test/test_index.py

@@ -101,8 +101,6 @@ class SeqTestCase:
         self.o2 = newstyle()
         self.n2 = newstyle()
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_index(self):
         self.o.ind = -2
         self.n.ind = 2
@@ -140,8 +138,6 @@ class SeqTestCase:
         self.assertEqual(self.o * self.seq, self.seq * 3)
         self.assertEqual(self.n * self.seq, self.seq * 2)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_wrappers(self):
         self.o.ind = 4
         self.n.ind = 5
@@ -169,8 +165,6 @@ class SeqTestCase:
 class ListTestCase(SeqTestCase, unittest.TestCase):
     seq = [0,10,20,30,40,50]
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_setdelitem(self):
         self.o.ind = -2
         self.n.ind = 2

vm/src/sliceable.rs

@@ -349,11 +349,21 @@ impl SequenceIndex {
                 .ok_or_else(|| vm
                     .new_index_error("cannot fit 'int' into an index-sized integer".to_owned())),
             s @ PySlice => Ok(SequenceIndex::Slice(s)),
-            obj => Err(vm.new_type_error(format!(
-                "{} indices must be integers or slices, not {}",
-                owner_type,
-                obj.class().name,
-            ))),
+            obj => {
+                let val = vm.to_index(&obj).map_err(|_| vm.new_type_error(format!(
+                    "{} indices must be integers or slices or classes that override __index__ operator, not '{}'",
+                    owner_type,
+                    obj.class().name
+                )))?;
+                val.as_bigint()
+                    .to_isize()
+                    .map(SequenceIndex::Int)
+                    .ok_or_else(|| {
+                        vm.new_index_error(
+                            "cannot fit 'int' into an index-sized integer".to_owned(),
+                        )
+                    })
+            }
         })
     }
 }