From 5bab0e940925df4649fb9d4c0fbfbd80190ddecd Mon Sep 17 00:00:00 2001
From: David Hewitt <1939362+davidhewitt@users.noreply.github.com>
Date: Fri, 3 Feb 2023 07:53:38 +0000
Subject: [PATCH] use simplified PyIter_Check on CPython 3.7

---
 newsfragments/2914.changed.md |  1 +
 pyo3-ffi/src/abstract_.rs     | 18 ++++++++----------
 src/types/iterator.rs         |  7 +------
 3 files changed, 10 insertions(+), 16 deletions(-)
 create mode 100644 newsfragments/2914.changed.md

diff --git a/newsfragments/2914.changed.md b/newsfragments/2914.changed.md
new file mode 100644
index 00000000000..bea926c4976
--- /dev/null
+++ b/newsfragments/2914.changed.md
@@ -0,0 +1 @@
+FFI definition `PyIter_Check` on CPython 3.7 now does the equivalent for `hasattr(type(obj), "__next__")`, which works correctly on all platforms and adds support for `abi3`.
diff --git a/pyo3-ffi/src/abstract_.rs b/pyo3-ffi/src/abstract_.rs
index 6f954bc1b47..24ad40057b1 100644
--- a/pyo3-ffi/src/abstract_.rs
+++ b/pyo3-ffi/src/abstract_.rs
@@ -92,19 +92,17 @@ extern "C" {
 }
 
 // Before 3.8 PyIter_Check was defined in CPython as a macro,
-// which uses Py_TYPE so cannot work on the limited ABI.
+// but the implementation of that in PyO3 did not work, see
+// https://github.com/PyO3/pyo3/pull/2914
 //
-// From 3.10 onwards CPython removed the macro completely,
-// so PyO3 only uses this on 3.7 unlimited API.
-#[cfg(not(any(Py_3_8, Py_LIMITED_API, PyPy)))]
+// This is a slow implementation which should function equivalently.
+#[cfg(not(any(Py_3_8, PyPy)))]
 #[inline]
 pub unsafe fn PyIter_Check(o: *mut PyObject) -> c_int {
-    (match (*crate::Py_TYPE(o)).tp_iternext {
-        Some(tp_iternext) => {
-            tp_iternext as *const std::os::raw::c_void != crate::_PyObject_NextNotImplemented as _
-        }
-        None => false,
-    }) as c_int
+    crate::PyObject_HasAttrString(
+        crate::Py_TYPE(o).cast(),
+        "__next__\0".as_ptr() as *const c_char,
+    )
 }
 
 extern "C" {
diff --git a/src/types/iterator.rs b/src/types/iterator.rs
index 9d68ca4f666..cfbbd31b6dc 100644
--- a/src/types/iterator.rs
+++ b/src/types/iterator.rs
@@ -3,7 +3,6 @@
 // based on Daniel Grunwald's https://github.com/dgrunwald/rust-cpython
 
 use crate::{ffi, AsPyPointer, IntoPyPointer, Py, PyAny, PyErr, PyNativeType, PyResult, Python};
-#[cfg(any(not(Py_LIMITED_API), Py_3_8))]
 use crate::{PyDowncastError, PyTryFrom};
 
 /// A Python iterator object.
@@ -29,7 +28,6 @@ use crate::{PyDowncastError, PyTryFrom};
 #[repr(transparent)]
 pub struct PyIterator(PyAny);
 pyobject_native_type_named!(PyIterator);
-#[cfg(any(not(Py_LIMITED_API), Py_3_8))]
 pyobject_native_type_extract!(PyIterator);
 
 impl PyIterator {
@@ -64,7 +62,6 @@ impl<'p> Iterator for &'p PyIterator {
 }
 
 // PyIter_Check does not exist in the limited API until 3.8
-#[cfg(any(not(Py_LIMITED_API), Py_3_8))]
 impl<'v> PyTryFrom<'v> for PyIterator {
     fn try_from<V: Into<&'v PyAny>>(value: V) -> Result<&'v PyIterator, PyDowncastError<'v>> {
         let value = value.into();
@@ -218,7 +215,7 @@ def fibonacci(target):
     }
 
     #[test]
-    #[cfg(any(not(Py_LIMITED_API), Py_3_8))]
+
     fn iterator_try_from() {
         Python::with_gil(|py| {
             let obj: Py<PyAny> = vec![10, 20].to_object(py).as_ref(py).iter().unwrap().into();
@@ -250,7 +247,6 @@ def fibonacci(target):
     }
 
     #[test]
-    #[cfg(any(not(Py_LIMITED_API), Py_3_8))]
     #[cfg(feature = "macros")]
     fn python_class_not_iterator() {
         use crate::PyErr;
@@ -298,7 +294,6 @@ def fibonacci(target):
     }
 
     #[test]
-    #[cfg(any(not(Py_LIMITED_API), Py_3_8))]
     #[cfg(feature = "macros")]
     fn python_class_iterator() {
         #[crate::pyfunction(crate = "crate")]