add c_str! macro to create &'static CStr (#4255)

* add `c_str!` macro to create `&'static CStr`

* newsfragment, just export as `pyo3::ffi::c_str`

* fix doc link

* fix doc

* further `c_str!` based cleanups

* [review]: mejrs

Co-authored-by: Bruno Kolenbrander <[email protected]>

* rustfmt

* build fixes

* clippy

* allow lint on MSRV

* fix GraalPy import

---------

Co-authored-by: Bruno Kolenbrander <[email protected]>

Author: davidhewitt

examples/sequential/src/id.rs

@@ -1,5 +1,6 @@
 use core::sync::atomic::{AtomicU64, Ordering};
 use core::{mem, ptr};
+use std::ffi::CString;
 use std::os::raw::{c_char, c_int, c_uint, c_ulonglong, c_void};
 
 use pyo3_ffi::*;
@@ -27,10 +28,10 @@ unsafe extern "C" fn id_new(
     kwds: *mut PyObject,
 ) -> *mut PyObject {
     if PyTuple_Size(args) != 0 || !kwds.is_null() {
-        PyErr_SetString(
-            PyExc_TypeError,
-            "Id() takes no arguments\0".as_ptr().cast::<c_char>(),
-        );
+        // We use pyo3-ffi's `c_str!` macro to create null-terminated literals because
+        // Rust's string literals are not null-terminated
+        // On Rust 1.77 or newer you can use `c"text"` instead.
+        PyErr_SetString(PyExc_TypeError, c_str!("Id() takes no arguments").as_ptr());
         return ptr::null_mut();
     }
 
@@ -81,8 +82,12 @@ unsafe extern "C" fn id_richcompare(
         pyo3_ffi::Py_GT => slf > other,
         pyo3_ffi::Py_GE => slf >= other,
         unrecognized => {
-            let msg = format!("unrecognized richcompare opcode {}\0", unrecognized);
-            PyErr_SetString(PyExc_SystemError, msg.as_ptr().cast::<c_char>());
+            let msg = CString::new(&*format!(
+                "unrecognized richcompare opcode {}",
+                unrecognized
+            ))
+            .unwrap();
+            PyErr_SetString(PyExc_SystemError, msg.as_ptr());
             return ptr::null_mut();
         }
     };
@@ -101,7 +106,7 @@ static mut SLOTS: &[PyType_Slot] = &[
     },
     PyType_Slot {
         slot: Py_tp_doc,
-        pfunc: "An id that is increased every time an instance is created\0".as_ptr()
+        pfunc: c_str!("An id that is increased every time an instance is created").as_ptr()
             as *mut c_void,
     },
     PyType_Slot {
@@ -123,7 +128,7 @@ static mut SLOTS: &[PyType_Slot] = &[
 ];
 
 pub static mut ID_SPEC: PyType_Spec = PyType_Spec {
-    name: "sequential.Id\0".as_ptr().cast::<c_char>(),
+    name: c_str!("sequential.Id").as_ptr(),
     basicsize: mem::size_of::<PyId>() as c_int,
     itemsize: 0,
     flags: (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_IMMUTABLETYPE) as c_uint,

examples/sequential/src/module.rs

@@ -1,13 +1,11 @@
 use core::{mem, ptr};
 use pyo3_ffi::*;
-use std::os::raw::{c_char, c_int, c_void};
+use std::os::raw::{c_int, c_void};
 
 pub static mut MODULE_DEF: PyModuleDef = PyModuleDef {
     m_base: PyModuleDef_HEAD_INIT,
-    m_name: "sequential\0".as_ptr().cast::<c_char>(),
-    m_doc: "A library for generating sequential ids, written in Rust.\0"
-        .as_ptr()
-        .cast::<c_char>(),
+    m_name: c_str!("sequential").as_ptr(),
+    m_doc: c_str!("A library for generating sequential ids, written in Rust.").as_ptr(),
     m_size: mem::size_of::<sequential_state>() as Py_ssize_t,
     m_methods: std::ptr::null_mut(),
     m_slots: unsafe { SEQUENTIAL_SLOTS as *const [PyModuleDef_Slot] as *mut PyModuleDef_Slot },
@@ -42,13 +40,13 @@ unsafe extern "C" fn sequential_exec(module: *mut PyObject) -> c_int {
     if id_type.is_null() {
         PyErr_SetString(
             PyExc_SystemError,
-            "cannot locate type object\0".as_ptr().cast::<c_char>(),
+            c_str!("cannot locate type object").as_ptr(),
         );
         return -1;
     }
     (*state).id_type = id_type.cast::<PyTypeObject>();
 
-    PyModule_AddObjectRef(module, "Id\0".as_ptr().cast::<c_char>(), id_type)
+    PyModule_AddObjectRef(module, c_str!("Id").as_ptr(), id_type)
 }
 
 unsafe extern "C" fn sequential_traverse(

examples/sequential/tests/test.rs

@@ -5,11 +5,13 @@ use std::thread;
 use pyo3_ffi::*;
 use sequential::PyInit_sequential;
 
-static COMMAND: &'static str = "
+static COMMAND: &'static str = c_str!(
+    "
 from sequential import Id
 
 s = sum(int(Id()) for _ in range(12))
-\0";
+"
+);
 
 // Newtype to be able to pass it to another thread.
 struct State(*mut PyThreadState);
@@ -19,10 +21,7 @@ unsafe impl Send for State {}
 #[test]
 fn lets_go_fast() -> Result<(), String> {
     unsafe {
-        let ret = PyImport_AppendInittab(
-            "sequential\0".as_ptr().cast::<c_char>(),
-            Some(PyInit_sequential),
-        );
+        let ret = PyImport_AppendInittab(c_str!("sequential").as_ptr(), Some(PyInit_sequential));
         if ret == -1 {
             return Err("could not add module to inittab".into());
         }
@@ -122,11 +121,8 @@ unsafe fn fetch() -> String {
 
 fn run_code() -> Result<u64, String> {
     unsafe {
-        let code_obj = Py_CompileString(
-            COMMAND.as_ptr().cast::<c_char>(),
-            "program\0".as_ptr().cast::<c_char>(),
-            Py_file_input,
-        );
+        let code_obj =
+            Py_CompileString(COMMAND.as_ptr(), c_str!("program").as_ptr(), Py_file_input);
         if code_obj.is_null() {
             return Err(fetch());
         }
@@ -138,7 +134,7 @@ fn run_code() -> Result<u64, String> {
         } else {
             Py_DECREF(res_ptr);
         }
-        let sum = PyDict_GetItemString(globals, "s\0".as_ptr().cast::<c_char>()); /* borrowed reference */
+        let sum = PyDict_GetItemString(globals, c_str!("s").as_ptr()); /* borrowed reference */
         if sum.is_null() {
             Py_DECREF(globals);
             return Err("globals did not have `s`".into());

examples/string-sum/src/lib.rs

@@ -5,10 +5,8 @@ use pyo3_ffi::*;
 
 static mut MODULE_DEF: PyModuleDef = PyModuleDef {
     m_base: PyModuleDef_HEAD_INIT,
-    m_name: "string_sum\0".as_ptr().cast::<c_char>(),
-    m_doc: "A Python module written in Rust.\0"
-        .as_ptr()
-        .cast::<c_char>(),
+    m_name: c_str!("string_sum").as_ptr(),
+    m_doc: c_str!("A Python module written in Rust.").as_ptr(),
     m_size: 0,
     m_methods: unsafe { METHODS as *const [PyMethodDef] as *mut PyMethodDef },
     m_slots: std::ptr::null_mut(),
@@ -19,14 +17,12 @@ static mut MODULE_DEF: PyModuleDef = PyModuleDef {
 
 static mut METHODS: &[PyMethodDef] = &[
     PyMethodDef {
-        ml_name: "sum_as_string\0".as_ptr().cast::<c_char>(),
+        ml_name: c_str!("sum_as_string").as_ptr(),
         ml_meth: PyMethodDefPointer {
             _PyCFunctionFast: sum_as_string,
         },
         ml_flags: METH_FASTCALL,
-        ml_doc: "returns the sum of two integers as a string\0"
-            .as_ptr()
-            .cast::<c_char>(),
+        ml_doc: c_str!("returns the sum of two integers as a string").as_ptr(),
     },
     // A zeroed PyMethodDef to mark the end of the array.
     PyMethodDef::zeroed(),
@@ -93,9 +89,7 @@ pub unsafe extern "C" fn sum_as_string(
     if nargs != 2 {
         PyErr_SetString(
             PyExc_TypeError,
-            "sum_as_string expected 2 positional arguments\0"
-                .as_ptr()
-                .cast::<c_char>(),
+            c_str!("sum_as_string expected 2 positional arguments").as_ptr(),
         );
         return std::ptr::null_mut();
     }
@@ -119,7 +113,7 @@ pub unsafe extern "C" fn sum_as_string(
         None => {
             PyErr_SetString(
                 PyExc_OverflowError,
-                "arguments too large to add\0".as_ptr().cast::<c_char>(),
+                c_str!("arguments too large to add").as_ptr(),
             );
             std::ptr::null_mut()
         }

guide/src/class.md

@@ -330,8 +330,8 @@ or [`PyRefMut`] instead of `&mut self`.
 Then you can access a parent class by `self_.as_super()` as `&PyRef<Self::BaseClass>`,
 or by `self_.into_super()` as `PyRef<Self::BaseClass>` (and similar for the `PyRefMut`
 case). For convenience, `self_.as_ref()` can also be used to get `&Self::BaseClass`
-directly; however, this approach does not let you access base clases higher in the 
-inheritance hierarchy, for which you would need to chain multiple `as_super` or 
+directly; however, this approach does not let you access base clases higher in the
+inheritance hierarchy, for which you would need to chain multiple `as_super` or
 `into_super` calls.
 
 ```rust
@@ -400,7 +400,7 @@ impl SubSubClass {
           let val2 = self_.as_super().val2;
           (val1, val2, self_.val3)
       }
-  
+
     fn double_values(mut self_: PyRefMut<'_, Self>) {
         self_.as_super().as_super().val1 *= 2;
         self_.as_super().val2 *= 2;
@@ -1187,7 +1187,7 @@ Python::with_gil(|py| {
 })
 ```
 
-Ordering of enum variants is optionally added using `#[pyo3(ord)]`.  
+Ordering of enum variants is optionally added using `#[pyo3(ord)]`.
 *Note: Implementation of the `PartialOrd` trait is required when passing the `ord` argument.  If not implemented, a compile time error is raised.*
 
 ```rust
@@ -1443,7 +1443,7 @@ impl pyo3::impl_::pyclass::PyClassImpl for MyClass {
         static DOC: pyo3::sync::GILOnceCell<::std::borrow::Cow<'static, ::std::ffi::CStr>> = pyo3::sync::GILOnceCell::new();
         DOC.get_or_try_init(py, || {
             let collector = PyClassImplCollector::<Self>::new();
-            build_pyclass_doc(<MyClass as pyo3::PyTypeInfo>::NAME, "\0", collector.new_text_signature())
+            build_pyclass_doc(<MyClass as pyo3::PyTypeInfo>::NAME, pyo3::ffi::c_str!(""), collector.new_text_signature())
         }).map(::std::ops::Deref::deref)
     }
 }

newsfragments/4255.added.md

@@ -0,0 +1 @@
+Add `pyo3_ffi::c_str` macro to create `&'static CStr` on Rust versions which don't have 1.77's `c""` literals.

newsfragments/4255.changed.md

@@ -0,0 +1 @@
+`PyCFunction::new`, `PyCFunction::new_with_keywords` and `PyCFunction::new_closure` now take `&'static CStr` name and doc arguments (previously was `&'static str`).

pyo3-ffi/README.md

@@ -51,10 +51,8 @@ use pyo3_ffi::*;
 
 static mut MODULE_DEF: PyModuleDef = PyModuleDef {
     m_base: PyModuleDef_HEAD_INIT,
-    m_name: "string_sum\0".as_ptr().cast::<c_char>(),
-    m_doc: "A Python module written in Rust.\0"
-        .as_ptr()
-        .cast::<c_char>(),
+    m_name: c_str!("string_sum").as_ptr(),
+    m_doc: c_str!("A Python module written in Rust.").as_ptr(),
     m_size: 0,
     m_methods: unsafe { METHODS.as_mut_ptr().cast() },
     m_slots: std::ptr::null_mut(),
@@ -65,14 +63,12 @@ static mut MODULE_DEF: PyModuleDef = PyModuleDef {
 
 static mut METHODS: [PyMethodDef; 2] = [
     PyMethodDef {
-        ml_name: "sum_as_string\0".as_ptr().cast::<c_char>(),
+        ml_name: c_str!("sum_as_string").as_ptr(),
         ml_meth: PyMethodDefPointer {
             _PyCFunctionFast: sum_as_string,
         },
         ml_flags: METH_FASTCALL,
-        ml_doc: "returns the sum of two integers as a string\0"
-            .as_ptr()
-            .cast::<c_char>(),
+        ml_doc: c_str!("returns the sum of two integers as a string").as_ptr(),
     },
     // A zeroed PyMethodDef to mark the end of the array.
     PyMethodDef::zeroed()
@@ -93,9 +89,7 @@ pub unsafe extern "C" fn sum_as_string(
     if nargs != 2 {
         PyErr_SetString(
             PyExc_TypeError,
-            "sum_as_string() expected 2 positional arguments\0"
-                .as_ptr()
-                .cast::<c_char>(),
+            c_str!("sum_as_string() expected 2 positional arguments").as_ptr(),
         );
         return std::ptr::null_mut();
     }
@@ -104,9 +98,7 @@ pub unsafe extern "C" fn sum_as_string(
     if PyLong_Check(arg1) == 0 {
         PyErr_SetString(
             PyExc_TypeError,
-            "sum_as_string() expected an int for positional argument 1\0"
-                .as_ptr()
-                .cast::<c_char>(),
+            c_str!("sum_as_string() expected an int for positional argument 1").as_ptr(),
         );
         return std::ptr::null_mut();
     }
@@ -120,9 +112,7 @@ pub unsafe extern "C" fn sum_as_string(
     if PyLong_Check(arg2) == 0 {
         PyErr_SetString(
             PyExc_TypeError,
-            "sum_as_string() expected an int for positional argument 2\0"
-                .as_ptr()
-                .cast::<c_char>(),
+            c_str!("sum_as_string() expected an int for positional argument 2").as_ptr(),
         );
         return std::ptr::null_mut();
     }
@@ -140,7 +130,7 @@ pub unsafe extern "C" fn sum_as_string(
         None => {
             PyErr_SetString(
                 PyExc_OverflowError,
-                "arguments too large to add\0".as_ptr().cast::<c_char>(),
+                c_str!("arguments too large to add").as_ptr(),
             );
             std::ptr::null_mut()
         }

pyo3-ffi/src/abstract_.rs

@@ -114,7 +114,7 @@ extern "C" {
 #[cfg(not(any(Py_3_8, PyPy)))]
 #[inline]
 pub unsafe fn PyIter_Check(o: *mut PyObject) -> c_int {
-    crate::PyObject_HasAttrString(crate::Py_TYPE(o).cast(), "__next__\0".as_ptr().cast())
+    crate::PyObject_HasAttrString(crate::Py_TYPE(o).cast(), c_str!("__next__").as_ptr())
 }
 
 extern "C" {