Use `Ident::parse_any` for `name` attributes (#4226)

This makes it possible to use rust keywords as the name of python class
methods and standalone functions. For example:

```
struct MyClass {
}

impl MyClass {
    #[new]
    fn new() -> Self {
        MyClass {}
    }

    #[pyo3(name = "struct")]
    fn struct_method(&self) -> usize {
        42
    }
}

fn struct_function() -> usize {
    42
}
```

From the [`syn::Ident`
documentation](https://docs.rs/syn/2.0.66/syn/struct.Ident.html):

> An identifier constructed with `Ident::new` is permitted to be a Rust
keyword, though parsing one through its
[`Parse`](https://docs.rs/syn/2.0.66/syn/parse/trait.Parse.html)
implementation rejects Rust keywords. Use `input.call(Ident::parse_any)`
when parsing to match the behaviour of `Ident::new`.

Fixes issue #4225

newsfragments/4226.fixed.md

@@ -0,0 +1 @@
+Fixes a compile error when declaring a standalone function or class method with a Python name that is a Rust keyword.

pyo3-macros-backend/src/attributes.rs

@@ -1,6 +1,7 @@
 use proc_macro2::TokenStream;
 use quote::ToTokens;
 use syn::{
+    ext::IdentExt,
     parse::{Parse, ParseStream},
     punctuated::Punctuated,
     spanned::Spanned,
@@ -72,7 +73,7 @@ pub struct NameLitStr(pub Ident);
 impl Parse for NameLitStr {
     fn parse(input: ParseStream<'_>) -> Result<Self> {
         let string_literal: LitStr = input.parse()?;
-        if let Ok(ident) = string_literal.parse() {
+        if let Ok(ident) = string_literal.parse_with(Ident::parse_any) {
             Ok(NameLitStr(ident))
         } else {
             bail_spanned!(string_literal.span() => "expected a single identifier in double quotes")

tests/test_class_basics.rs

@@ -123,6 +123,36 @@ fn custom_names() {
     });
 }
 
+#[pyclass(name = "loop")]
+struct ClassRustKeywords {
+    #[pyo3(name = "unsafe", get, set)]
+    unsafe_variable: usize,
+}
+
+#[pymethods]
+impl ClassRustKeywords {
+    #[pyo3(name = "struct")]
+    fn struct_method(&self) {}
+
+    #[staticmethod]
+    #[pyo3(name = "type")]
+    fn type_method() {}
+}
+
+#[test]
+fn keyword_names() {
+    Python::with_gil(|py| {
+        let typeobj = py.get_type_bound::<ClassRustKeywords>();
+        py_assert!(py, typeobj, "typeobj.__name__ == 'loop'");
+        py_assert!(py, typeobj, "typeobj.struct.__name__ == 'struct'");
+        py_assert!(py, typeobj, "typeobj.type.__name__ == 'type'");
+        py_assert!(py, typeobj, "typeobj.unsafe.__name__ == 'unsafe'");
+        py_assert!(py, typeobj, "not hasattr(typeobj, 'unsafe_variable')");
+        py_assert!(py, typeobj, "not hasattr(typeobj, 'struct_method')");
+        py_assert!(py, typeobj, "not hasattr(typeobj, 'type_method')");
+    });
+}
+
 #[pyclass]
 struct RawIdents {
     #[pyo3(get, set)]

tests/test_pyfunction.rs

@@ -14,6 +14,18 @@ use pyo3::types::{self, PyCFunction};
 #[path = "../src/tests/common.rs"]
 mod common;
 
+#[pyfunction(name = "struct")]
+fn struct_function() {}
+
+#[test]
+fn test_rust_keyword_name() {
+    Python::with_gil(|py| {
+        let f = wrap_pyfunction_bound!(struct_function)(py).unwrap();
+
+        py_assert!(py, f, "f.__name__ == 'struct'");
+    });
+}
+
 #[pyfunction(signature = (arg = true))]
 fn optional_bool(arg: Option<bool>) -> String {
     format!("{:?}", arg)