Add clear(), add() and discard() for frozenset

These are actually available via the C ABI. Since the distinction between set and frozenset means nothing to Rust safety, we should make these available

newsfragments/3156.added.md

@@ -0,0 +1 @@
+Add `clear()`, `add()`, `pop()` and `discard()` for frozenset, which are all valid operations at the C ABI level according to the [C API docs for sets](https://docs.python.org/3/c-api/set.html)

src/types/frozenset.rs

@@ -74,6 +74,47 @@ impl PyFrozenSet {
         }
     }
 
+    /// Removes the element from the set if it is present.
+    pub fn discard<K>(&self, key: K)
+    where
+        K: ToPyObject,
+    {
+        unsafe {
+            ffi::PySet_Discard(self.as_ptr(), key.to_object(self.py()).as_ptr());
+        }
+    }
+
+    /// Adds an element to the set.
+    pub fn add<K>(&self, key: K) -> PyResult<()>
+    where
+        K: ToPyObject,
+    {
+        unsafe {
+            err::error_on_minusone(
+                self.py(),
+                ffi::PySet_Add(self.as_ptr(), key.to_object(self.py()).as_ptr()),
+            )
+        }
+    }
+
+    /// Removes and returns an arbitrary element from the set.
+    pub fn pop(&self) -> Option<PyObject> {
+        let element =
+            unsafe { PyObject::from_owned_ptr_or_err(self.py(), ffi::PySet_Pop(self.as_ptr())) };
+        match element {
+            Ok(e) => Some(e),
+            Err(_) => None,
+        }
+    }
+
+    /// Removes all elements from the set.
+    #[inline]
+    pub fn clear(&self) {
+        unsafe {
+            ffi::PySet_Clear(self.as_ptr());
+        }
+    }
+
     /// Returns an iterator of values in this frozen set.
     pub fn iter(&self) -> PyFrozenSetIterator<'_> {
         IntoIterator::into_iter(self)
@@ -206,6 +247,16 @@ mod tests {
         });
     }
 
+    #[test]
+    fn test_frozenset_clear() {
+        Python::with_gil(|py| {
+            let set = PyFrozenSet::new(py, &[1]).unwrap();
+            assert_eq!(1, set.len());
+            set.clear();
+            assert_eq!(0, set.len());
+        });
+    }
+
     #[test]
     fn test_frozenset_empty() {
         Python::with_gil(|py| {
@@ -222,6 +273,40 @@ mod tests {
         });
     }
 
+    #[test]
+    fn test_frozenset_discard() {
+        Python::with_gil(|py| {
+            let set = PyFrozenSet::new(py, &[1]).unwrap();
+            set.discard(2);
+            assert_eq!(1, set.len());
+            set.discard(1);
+            assert_eq!(0, set.len());
+        });
+    }
+
+    #[test]
+    fn test_frozenset_add() {
+        Python::with_gil(|py| {
+            let set = PyFrozenSet::new(py, &[1, 2]).unwrap();
+            set.add(1).unwrap(); // Add a dupliated element
+            assert!(set.contains(1).unwrap());
+        });
+    }
+
+    #[test]
+    fn test_frozenset_pop() {
+        Python::with_gil(|py| {
+            let set = PyFrozenSet::new(py, &[1]).unwrap();
+            let val = set.pop();
+            assert!(val.is_some());
+            let val2 = set.pop();
+            assert!(val2.is_none());
+            assert!(py
+                .eval("print('Exception state should not be set.')", None, None)
+                .is_ok());
+        });
+    }
+
     #[test]
     fn test_frozenset_iter() {
         Python::with_gil(|py| {

src/types/set.rs

@@ -46,14 +46,6 @@ impl PySet {
         unsafe { py.from_owned_ptr_or_err(ffi::PySet_New(ptr::null_mut())) }
     }
 
-    /// Removes all elements from the set.
-    #[inline]
-    pub fn clear(&self) {
-        unsafe {
-            ffi::PySet_Clear(self.as_ptr());
-        }
-    }
-
     /// Returns the number of items in the set.
     ///
     /// This is equivalent to the Python expression `len(self)`.
@@ -116,6 +108,14 @@ impl PySet {
         }
     }
 
+    /// Removes all elements from the set.
+    #[inline]
+    pub fn clear(&self) {
+        unsafe {
+            ffi::PySet_Clear(self.as_ptr());
+        }
+    }
+
     /// Returns an iterator of values in this set.
     ///
     /// # Panics