Eagerly expand cfg/cfg_attr in pyclasses

newsfragments/6134.changed.md

@@ -0,0 +1 @@
+The `#[pyclass]` macro will now eagerly evaluate `cfg` and `cfg_attr` on fields and enum variants. 

pyo3-macros-backend/src/lib.rs

@@ -6,7 +6,7 @@
 
 // Listed first so that macros in this module are available in the rest of the crate.
 #[macro_use]
-mod utils;
+pub mod utils;
 
 mod attributes;
 mod combine_errors;
@@ -30,7 +30,7 @@ mod quotes;
 pub use frompyobject::build_derive_from_pyobject;
 pub use intopyobject::build_derive_into_pyobject;
 pub use module::{pymodule_function_impl, pymodule_module_impl, PyModuleOptions};
-pub use pyclass::{build_py_class, build_py_enum, PyClassArgs};
+pub use pyclass::{build_py_class, build_py_enum, PyClassArgs, PyClassKind, PyClassPyO3Options};
 pub use pyfunction::{build_py_function, PyFunctionOptions};
 pub use pyimpl::{build_py_methods, PyClassMethodsType};
 pub use utils::get_doc;

pyo3-macros-backend/src/pyclass.rs

@@ -3211,6 +3211,7 @@ fn generate_cfg_check(variants: &[PyClassEnumUnitVariant<'_>], cls: &syn::Ident)
         }
     }
 
+    // Should be unreachable; we eagerly expand cfgs now.
     quote_spanned! {
         cls.span() =>
         #[cfg(all(#(#conditions),*))]

pyo3-macros-backend/src/utils.rs

@@ -201,10 +201,7 @@ pub struct Ctx {
 
 impl Ctx {
     pub(crate) fn new(attr: &Option<CrateAttribute>, signature: Option<&syn::Signature>) -> Self {
-        let pyo3_path = match attr {
-            Some(attr) => PyO3CratePath::Given(attr.value.0.clone()),
-            None => PyO3CratePath::Default,
-        };
+        let pyo3_path = PyO3CratePath::from_crate_path(attr);
 
         let output_span = if let Some(syn::Signature {
             output: syn::ReturnType::Type(_, output_type),
@@ -230,6 +227,12 @@ pub enum PyO3CratePath {
 }
 
 impl PyO3CratePath {
+    pub fn from_crate_path(path: &Option<CrateAttribute>) -> Self {
+        match path {
+            Some(attr) => PyO3CratePath::Given(attr.value.0.clone()),
+            None => PyO3CratePath::Default,
+        }
+    }
     pub fn to_tokens_spanned(&self, span: Span) -> TokenStream {
         match self {
             Self::Given(path) => quote::quote_spanned! { span => #path },

pyo3-macros/Cargo.toml

@@ -22,7 +22,7 @@ experimental-inspect = ["pyo3-macros-backend/experimental-inspect"]
 [dependencies]
 proc-macro2 = { version = "1.0.60", default-features = false }
 quote = "1"
-syn = { version = "2", features = ["full", "extra-traits"] }
+syn = { version = "2", features = ["full", "extra-traits", "visit", "visit-mut"] }
 pyo3-macros-backend = { path = "../pyo3-macros-backend", version = "=0.29.0" }
 
 [lints]