Adds timezone_from_offset and timezone_from_offset_and_name functions

Exposes C functions provided by datetime.h

It allows to build conversions from chrono without direct access to the C API

newsfragments/3648.added.md

@@ -0,0 +1 @@
+Add `timezone_from_offset` and `timezone_from_offset_and_name` to construct `datetime.timezone` objects

src/conversions/chrono.rs

@@ -42,15 +42,14 @@
 //! ```
 use crate::exceptions::{PyTypeError, PyUserWarning, PyValueError};
 use crate::types::{
-    timezone_utc, PyDate, PyDateAccess, PyDateTime, PyDelta, PyDeltaAccess, PyTime, PyTimeAccess,
-    PyTzInfo, PyTzInfoAccess, PyUnicode,
+    timezone_from_offset, timezone_utc, PyDate, PyDateAccess, PyDateTime, PyDelta, PyDeltaAccess,
+    PyTime, PyTimeAccess, PyTzInfo, PyTzInfoAccess, PyUnicode,
 };
 use crate::{FromPyObject, IntoPy, PyAny, PyErr, PyObject, PyResult, Python, ToPyObject};
 use chrono::offset::{FixedOffset, Utc};
 use chrono::{
     DateTime, Datelike, Duration, NaiveDate, NaiveDateTime, NaiveTime, Offset, TimeZone, Timelike,
 };
-use pyo3_ffi::{PyDateTime_IMPORT, PyTimeZone_FromOffset};
 use std::convert::TryInto;
 
 impl ToPyObject for Duration {
@@ -231,22 +230,14 @@ impl FromPyObject<'_> for DateTime<Utc> {
     }
 }
 
-// Utility function used to convert PyDelta to timezone
-fn py_timezone_from_offset<'a>(py: &Python<'a>, td: &PyDelta) -> &'a PyAny {
-    // Safety: py.from_owned_ptr needs the cast to be valid.
-    // Since we are forcing a &PyDelta as input, the cast should always be valid.
-    unsafe {
-        PyDateTime_IMPORT();
-        py.from_owned_ptr(PyTimeZone_FromOffset(td.as_ptr()))
-    }
-}
-
 impl ToPyObject for FixedOffset {
     fn to_object(&self, py: Python<'_>) -> PyObject {
         let seconds_offset = self.local_minus_utc();
         let td =
             PyDelta::new(py, 0, seconds_offset, 0, true).expect("failed to construct timedelta");
-        py_timezone_from_offset(&py, td).into()
+        timezone_from_offset(py, td)
+            .expect("Failed to construct PyTimezone")
+            .into()
     }
 }
 
@@ -847,14 +838,14 @@ mod tests {
             let offset = FixedOffset::east_opt(3600).unwrap().to_object(py);
             // Python timezone from timedelta
             let td = PyDelta::new(py, 0, 3600, 0, true).unwrap();
-            let py_timedelta = py_timezone_from_offset(&py, td);
+            let py_timedelta = timezone_from_offset(py, td).unwrap();
             // Should be equal
             assert!(offset.as_ref(py).eq(py_timedelta).unwrap());
 
             // Same but with negative values
             let offset = FixedOffset::east_opt(-3600).unwrap().to_object(py);
             let td = PyDelta::new(py, 0, -3600, 0, true).unwrap();
-            let py_timedelta = py_timezone_from_offset(&py, td);
+            let py_timedelta = timezone_from_offset(py, td).unwrap();
             assert!(offset.as_ref(py).eq(py_timedelta).unwrap());
         })
     }
@@ -863,7 +854,7 @@ mod tests {
     fn test_pyo3_offset_fixed_frompyobject() {
         Python::with_gil(|py| {
             let py_timedelta = PyDelta::new(py, 0, 3600, 0, true).unwrap();
-            let py_tzinfo = py_timezone_from_offset(&py, py_timedelta);
+            let py_tzinfo = timezone_from_offset(py, py_timedelta).unwrap();
             let offset: FixedOffset = py_tzinfo.extract().unwrap();
             assert_eq!(FixedOffset::east_opt(3600).unwrap(), offset);
         })
@@ -886,12 +877,12 @@ mod tests {
             assert_eq!(Utc, py_utc);
 
             let py_timedelta = PyDelta::new(py, 0, 0, 0, true).unwrap();
-            let py_timezone_utc = py_timezone_from_offset(&py, py_timedelta);
+            let py_timezone_utc = timezone_from_offset(py, py_timedelta).unwrap();
             let py_timezone_utc: Utc = py_timezone_utc.extract().unwrap();
             assert_eq!(Utc, py_timezone_utc);
 
             let py_timedelta = PyDelta::new(py, 0, 3600, 0, true).unwrap();
-            let py_timezone = py_timezone_from_offset(&py, py_timedelta);
+            let py_timezone = timezone_from_offset(py, py_timedelta).unwrap();
             assert!(py_timezone.extract::<Utc>().is_err());
         })
     }

src/types/datetime.rs

@@ -20,9 +20,10 @@ use crate::ffi::{
     PyDateTime_TIME_GET_MINUTE, PyDateTime_TIME_GET_SECOND,
 };
 use crate::instance::PyNativeType;
-use crate::types::PyTuple;
-use crate::{IntoPy, Py, PyAny, Python};
+use crate::types::{PyString, PyTuple};
+use crate::{AsPyPointer, IntoPy, Py, PyAny, Python};
 use std::os::raw::c_int;
+use std::ptr;
 
 fn ensure_datetime_api(_py: Python<'_>) -> &'static PyDateTime_CAPI {
     unsafe {
@@ -487,6 +488,32 @@ pub fn timezone_utc(py: Python<'_>) -> &PyTzInfo {
     unsafe { &*(ensure_datetime_api(py).TimeZone_UTC as *const PyTzInfo) }
 }
 
+/// Equivalent to `datetime.timezone` constructor
+///
+/// Use [`timezone_from_offset_and_name`] for a named timezones.
+pub fn timezone_from_offset<'a>(py: Python<'a>, offset: &PyDelta) -> PyResult<&'a PyTzInfo> {
+    let api = ensure_datetime_api(py);
+    unsafe {
+        let ptr = (api.TimeZone_FromTimeZone)(offset.as_ptr(), ptr::null_mut());
+        py.from_owned_ptr_or_err(ptr)
+    }
+}
+
+/// Equivalent to `datetime.timezone` constructor with a timezone name
+///
+/// Use [`timezone_from_offset`] for offset-only timezones.
+pub fn timezone_from_offset_and_name<'a>(
+    py: Python<'a>,
+    offset: &PyDelta,
+    name: &PyString,
+) -> PyResult<&'a PyTzInfo> {
+    let api = ensure_datetime_api(py);
+    unsafe {
+        let ptr = (api.TimeZone_FromTimeZone)(offset.as_ptr(), name.as_ptr());
+        py.from_owned_ptr_or_err(ptr)
+    }
+}
+
 /// Bindings for `datetime.timedelta`
 #[repr(transparent)]
 pub struct PyDelta(PyAny);
@@ -620,4 +647,77 @@ mod tests {
             assert!(t.get_tzinfo().is_none());
         });
     }
+
+    #[test]
+    #[cfg(feature = "macros")]
+    #[cfg_attr(target_arch = "wasm32", ignore)] // DateTime import fails on wasm for mysterious reasons
+    fn test_timezone_from_offset() {
+        Python::with_gil(|py| {
+            assert_timezone_eq(
+                py,
+                timezone_from_offset(py, PyDelta::new(py, 0, -3600, 0, true).unwrap()).unwrap(),
+                -3600,
+                "UTC-01:00",
+            );
+            assert_timezone_eq(
+                py,
+                timezone_from_offset(py, PyDelta::new(py, 0, 3600, 0, true).unwrap()).unwrap(),
+                3600,
+                "UTC+01:00",
+            );
+            timezone_from_offset(py, PyDelta::new(py, 1, 0, 0, true).unwrap()).unwrap_err();
+        })
+    }
+
+    #[test]
+    #[cfg(feature = "macros")]
+    #[cfg_attr(target_arch = "wasm32", ignore)] // DateTime import fails on wasm for mysterious reasons
+    fn test_timezone_from_offset_and_name() {
+        Python::with_gil(|py| {
+            let name = PyString::new(py, "foo");
+            assert_timezone_eq(
+                py,
+                timezone_from_offset_and_name(
+                    py,
+                    PyDelta::new(py, 0, -3600, 0, true).unwrap(),
+                    name,
+                )
+                .unwrap(),
+                -3600,
+                "foo",
+            );
+            assert_timezone_eq(
+                py,
+                timezone_from_offset_and_name(
+                    py,
+                    PyDelta::new(py, 0, 3600, 0, true).unwrap(),
+                    name,
+                )
+                .unwrap(),
+                3600,
+                "foo",
+            );
+            timezone_from_offset_and_name(py, PyDelta::new(py, 1, 0, 0, true).unwrap(), name)
+                .unwrap_err();
+        })
+    }
+
+    #[cfg(feature = "macros")]
+    #[cfg_attr(target_arch = "wasm32", ignore)] // DateTime import fails on wasm for mysterious reasons
+    fn assert_timezone_eq(py: Python<'_>, timezone: &PyTzInfo, delta_s: i32, name: &str) {
+        let actual_delta = timezone
+            .call_method1("utcoffset", ((),))
+            .unwrap()
+            .extract::<&PyDelta>()
+            .unwrap();
+        let actual_name = timezone
+            .call_method1("tzname", ((),))
+            .unwrap()
+            .extract::<&str>()
+            .unwrap();
+        assert!(actual_delta
+            .eq(PyDelta::new(py, 0, delta_s, 0, true).unwrap())
+            .unwrap());
+        assert_eq!(actual_name, name);
+    }
 }

src/types/mod.rs

@@ -10,8 +10,8 @@ pub use self::code::PyCode;
 pub use self::complex::PyComplex;
 #[cfg(not(Py_LIMITED_API))]
 pub use self::datetime::{
-    timezone_utc, PyDate, PyDateAccess, PyDateTime, PyDelta, PyDeltaAccess, PyTime, PyTimeAccess,
-    PyTzInfo, PyTzInfoAccess,
+    timezone_from_offset, timezone_from_offset_and_name, timezone_utc, PyDate, PyDateAccess,
+    PyDateTime, PyDelta, PyDeltaAccess, PyTime, PyTimeAccess, PyTzInfo, PyTzInfoAccess,
 };
 pub use self::dict::{IntoPyDict, PyDict};
 #[cfg(not(PyPy))]