document and test raw idents with signature

guide/src/function/signature.md

@@ -94,6 +94,18 @@ num=44
 num=-1
 ```
 
+> Note: for keywords like `struct`, to use it as a function argument, use "raw ident" syntax `r#struct` in both the signature and the function definition:
+>
+> ```rust
+> # !#[allow(unused_code)]
+> # use pyo3::prelude::*;
+> #[pyfunction(signature = (r#struct = "foo"))]
+> fn method_with_keyword<'a>(&self, r#struct: &'a str) {
+> #     let _ = r#struct;
+>     /* ... */
+> }
+> ```
+
 ## Deprecated form
 
 The `#[pyfunction]` macro can take the argument specification directly, but this method is deprecated in PyO3 0.18 because the `#[pyo3(signature)]` option offers a simpler syntax and better validation.

pyo3-macros-backend/src/pyfunction/signature.rs

@@ -348,11 +348,11 @@ impl<'a> FunctionSignature<'a> {
         let mut next_argument_checked = |name: &syn::Ident| match args_iter.next() {
             Some(fn_arg) => {
                 ensure_spanned!(
-                    name == &fn_arg.name.unraw(),
+                    name == fn_arg.name,
                     name.span() => format!(
                         "expected argument from function definition `{}` but got argument `{}`",
                         fn_arg.name.unraw(),
-                        name,
+                        name.unraw(),
                     )
                 );
                 Ok(fn_arg)

tests/test_methods.rs

@@ -1344,6 +1344,11 @@ impl r#RawIdents {
 
     #[classattr]
     const r#CLASS_ATTR_CONST: i32 = 6;
+
+    #[pyo3(signature = (r#struct = "foo"))]
+    fn method_with_keyword<'a>(&self, r#struct: &'a str) -> &'a str {
+        r#struct
+    }
 }
 
 #[test]
@@ -1377,6 +1382,10 @@ fn test_raw_idents() {
 
             assert raw_idents_type.class_attr_fn == 5
             assert raw_idents_type.CLASS_ATTR_CONST == 6
+
+            assert instance.method_with_keyword() == "foo"
+            assert instance.method_with_keyword("bar") == "bar"
+            assert instance.method_with_keyword(struct="baz") == "baz"
             "#
         );
     })