From fdc08139a5ba3f526f1846a867248d595116b64c Mon Sep 17 00:00:00 2001
From: jfh <jfh@imijmi.eu>
Date: Thu, 17 Jun 2021 17:30:51 +0300
Subject: [PATCH 1/2] Make empty frozenset a singleton.

---
 Lib/test/test_set.py   |  2 --
 vm/src/builtins/set.rs | 26 ++++++++++++++------------
 vm/src/pyobject.rs     |  6 +++++-
 3 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/Lib/test/test_set.py b/Lib/test/test_set.py
index a399d1caf..73a15d1ef 100644
--- a/Lib/test/test_set.py
+++ b/Lib/test/test_set.py
@@ -715,8 +715,6 @@ class TestFrozenSet(TestJointOps, unittest.TestCase):
         s.__init__(self.otherword)
         self.assertEqual(s, set(self.word))
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_singleton_empty_frozenset(self):
         f = frozenset()
         efs = [frozenset(), frozenset([]), frozenset(()), frozenset(''),
diff --git a/vm/src/builtins/set.rs b/vm/src/builtins/set.rs
index f322c1f14..0d2f3bff5 100644
--- a/vm/src/builtins/set.rs
+++ b/vm/src/builtins/set.rs
@@ -5,7 +5,6 @@ use super::pytype::PyTypeRef;
 use crate::common::hash::PyHash;
 use crate::common::rc::PyRc;
 use crate::dictdatatype;
-use crate::function::OptionalArg::{Missing, Present};
 use crate::function::{Args, OptionalArg};
 use crate::slots::{Comparable, Hashable, Iterable, PyComparisonOp, PyIter, Unhashable};
 use crate::vm::{ReprGuard, VirtualMachine};
@@ -573,23 +572,26 @@ impl PyFrozenSet {
         iterable: OptionalArg<PyObjectRef>,
         vm: &VirtualMachine,
     ) -> PyResult<PyRef<Self>> {
-        let iterable = if let Present(iterable) = iterable {
-            if cls.is(&vm.ctx.types.frozenset_type) {
-                match iterable.downcast_exact::<PyFrozenSet>(vm) {
-                    Ok(iter) => return Ok(iter),
-                    Err(iterable) => Present(PyIterable::try_from_object(vm, iterable)?),
+        let elements = if let OptionalArg::Present(iterable) = iterable {
+            let iterable = if cls.is(&vm.ctx.types.frozenset_type) {
+                match iterable.downcast_exact::<Self>(vm) {
+                    Ok(fs) => return Ok(fs),
+                    Err(iterable) => iterable,
                 }
             } else {
-                Present(PyIterable::try_from_object(vm, iterable)?)
-            }
+                iterable
+            };
+            vm.extract_elements(&iterable)?
         } else {
-            Missing
+            vec![]
         };
 
-        Self {
-            inner: PySetInner::from_arg(iterable, vm)?,
+        // Return empty fs if iterable passed is emtpy and only for exact fs types.
+        if elements.is_empty() && cls.is(&vm.ctx.types.frozenset_type) {
+            Ok(vm.ctx.empty_frozenset.clone())
+        } else {
+            Self::from_iter(vm, elements).and_then(|o| o.into_ref_with_type(vm, cls))
         }
-        .into_ref_with_type(vm, cls)
     }
 
     #[pymethod(name = "__len__")]
diff --git a/vm/src/pyobject.rs b/vm/src/pyobject.rs
index 2c1d33ee2..df823f1be 100644
--- a/vm/src/pyobject.rs
+++ b/vm/src/pyobject.rs
@@ -24,7 +24,7 @@ use crate::builtins::namespace::PyNamespace;
 use crate::builtins::object;
 use crate::builtins::pystr;
 use crate::builtins::pytype::{self, PyType, PyTypeRef};
-use crate::builtins::set;
+use crate::builtins::set::{self, PyFrozenSet};
 use crate::builtins::singletons::{PyNone, PyNoneRef, PyNotImplemented, PyNotImplementedRef};
 use crate::builtins::slice::PyEllipsis;
 use crate::builtins::staticmethod::PyStaticMethod;
@@ -89,6 +89,7 @@ pub struct PyContext {
     pub false_value: PyIntRef,
     pub none: PyNoneRef,
     pub empty_tuple: PyTupleRef,
+    pub empty_frozenset: PyRef<PyFrozenSet>,
     pub ellipsis: PyRef<PyEllipsis>,
     pub not_implemented: PyNotImplementedRef,
 
@@ -129,6 +130,8 @@ impl PyContext {
             PyTuple::_new(Vec::new().into_boxed_slice()),
             &types.tuple_type,
         );
+        let empty_frozenset =
+            PyRef::new_ref(PyFrozenSet::default(), types.frozenset_type.clone(), None);
 
         let string_cache = Dict::default();
 
@@ -144,6 +147,7 @@ impl PyContext {
             false_value,
             none,
             empty_tuple,
+            empty_frozenset,
             ellipsis,
             not_implemented,
 

From 712f95036d00abd8ff7dd8036e8ba48e20109d45 Mon Sep 17 00:00:00 2001
From: jfh <jfh@imijmi.eu>
Date: Mon, 12 Jul 2021 00:25:34 +0300
Subject: [PATCH 2/2] Remove allow_dead_code as it is unecessary now.

---
 vm/src/builtins/set.rs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/vm/src/builtins/set.rs b/vm/src/builtins/set.rs
index 0d2f3bff5..8d26c5e1a 100644
--- a/vm/src/builtins/set.rs
+++ b/vm/src/builtins/set.rs
@@ -553,8 +553,7 @@ macro_rules! multi_args_frozenset {
 
 #[pyimpl(flags(BASETYPE), with(Hashable, Comparable, Iterable))]
 impl PyFrozenSet {
-    // used by ssl.rs windows
-    #[allow(dead_code)]
+    // Also used by ssl.rs windows.
     pub(crate) fn from_iter(
         vm: &VirtualMachine,
         it: impl IntoIterator<Item = PyObjectRef>,