pyfunction: allow wrap_pyfunction to work on imports (even cross-crate)

CHANGELOG.md

@@ -27,6 +27,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add buffer magic methods `__getbuffer__` and `__releasebuffer__` to `#[pymethods]`. [#2067](https://github.com/PyO3/pyo3/pull/2067)
 - Accept paths in `wrap_pyfunction` and `wrap_pymodule`. [#2081](https://github.com/PyO3/pyo3/pull/2081)
 - Add check for correct number of arguments on magic methods. [#2083](https://github.com/PyO3/pyo3/pull/2083)
+- `wrap_pyfunction!` can now wrap a `#[pyfunction]` which is implemented in a different Rust module or crate. [#2091](https://github.com/PyO3/pyo3/pull/2091)
 
 ### Changed
 

pyo3-macros-backend/src/module.rs

@@ -99,10 +99,11 @@ pub fn process_functions_in_module(func: &mut syn::ItemFn) -> syn::Result<()> {
         if let syn::Stmt::Item(syn::Item::Fn(func)) = &mut stmt {
             if let Some(pyfn_args) = get_pyfn_attr(&mut func.attrs)? {
                 let module_name = pyfn_args.modname;
-                let (ident, wrapped_function) = impl_wrap_pyfunction(func, pyfn_args.options)?;
+                let wrapped_function = impl_wrap_pyfunction(func, pyfn_args.options)?;
+                let name = &func.sig.ident;
                 let statements: Vec<syn::Stmt> = syn::parse_quote! {
                     #wrapped_function
-                    #module_name.add_function(#ident(#module_name)?)?;
+                    #module_name.add_function(#name::wrap(#name::DEF, #module_name)?)?;
                 };
                 stmts.extend(statements);
             }

pyo3-macros-backend/src/pyfunction.rs

@@ -9,12 +9,11 @@ use crate::{
     method::{self, CallingConvention, FnArg},
     pymethod::check_generic,
     utils::{self, ensure_not_async_fn, get_pyo3_crate},
-    wrap::function_wrapper_ident,
 };
 use proc_macro2::{Span, TokenStream};
 use quote::{format_ident, quote};
 use syn::punctuated::Punctuated;
-use syn::{ext::IdentExt, spanned::Spanned, Ident, NestedMeta, Path, Result};
+use syn::{ext::IdentExt, spanned::Spanned, NestedMeta, Path, Result};
 use syn::{
     parse::{Parse, ParseBuffer, ParseStream},
     token::Comma,
@@ -364,15 +363,15 @@ pub fn build_py_function(
     mut options: PyFunctionOptions,
 ) -> syn::Result<TokenStream> {
     options.add_attributes(take_pyo3_options(&mut ast.attrs)?)?;
-    Ok(impl_wrap_pyfunction(ast, options)?.1)
+    impl_wrap_pyfunction(ast, options)
 }
 
 /// Generates python wrapper over a function that allows adding it to a python module as a python
 /// function
 pub fn impl_wrap_pyfunction(
     func: &mut syn::ItemFn,
     options: PyFunctionOptions,
-) -> syn::Result<(Ident, TokenStream)> {
+) -> syn::Result<TokenStream> {
     check_generic(&func.sig)?;
     ensure_not_async_fn(&func.sig)?;
 
@@ -412,7 +411,6 @@ pub fn impl_wrap_pyfunction(
             .map(|attr| (&python_name, attr)),
     );
 
-    let function_wrapper_ident = function_wrapper_ident(&func.sig.ident);
     let krate = get_pyo3_crate(&options.krate);
 
     let spec = method::FnSpec {
@@ -434,21 +432,40 @@ pub fn impl_wrap_pyfunction(
         unsafety: func.sig.unsafety,
     };
 
-    let wrapper_ident = format_ident!("__pyo3_raw_{}", spec.name);
+    let vis = &func.vis;
+    let name = &func.sig.ident;
+
+    let wrapper_ident = format_ident!("__pyfunction_{}", spec.name);
     let wrapper = spec.get_wrapper_function(&wrapper_ident, None)?;
     let methoddef = spec.get_methoddef(wrapper_ident);
 
     let wrapped_pyfunction = quote! {
         #wrapper
 
-        pub(crate) fn #function_wrapper_ident<'a>(
-            args: impl ::std::convert::Into<#krate::derive_utils::PyFunctionArguments<'a>>
-        ) -> #krate::PyResult<&'a #krate::types::PyCFunction> {
+        // Create a module with the same name as the `#[pyfunction]` - this way `use <the function>`
+        // will actually bring both the module and the function into scope.
+        #[doc(hidden)]
+        #vis mod #name {
             use #krate as _pyo3;
-            _pyo3::types::PyCFunction::internal_new(#methoddef, args.into())
+            pub(crate) struct PyO3Def;
+
+            // Exported for `wrap_pyfunction!`
+            pub use _pyo3::impl_::pyfunction::wrap_pyfunction as wrap;
+            pub const DEF: _pyo3::PyMethodDef = <PyO3Def as _pyo3::impl_::pyfunction::PyFunctionDef>::DEF;
         }
+
+        // Generate the definition inside an anonymous function in the same scope as the original function -
+        // this avoids complications around the fact that the generated module has a different scope
+        // (and `super` doesn't always refer to the outer scope, e.g. if the `#[pyfunction] is
+        // inside a function body)
+        const _: () = {
+            use #krate as _pyo3;
+            impl _pyo3::impl_::pyfunction::PyFunctionDef for #name::PyO3Def {
+                const DEF: _pyo3::PyMethodDef = #methoddef;
+            }
+        };
     };
-    Ok((function_wrapper_ident, wrapped_pyfunction))
+    Ok(wrapped_pyfunction)
 }
 
 fn type_is_pymodule(ty: &syn::Type) -> bool {

pyo3-macros-backend/src/wrap.rs

@@ -22,25 +22,16 @@ impl Parse for WrapPyFunctionArgs {
     }
 }
 
-pub fn wrap_pyfunction_impl(args: WrapPyFunctionArgs) -> syn::Result<TokenStream> {
+pub fn wrap_pyfunction_impl(args: WrapPyFunctionArgs) -> TokenStream {
     let WrapPyFunctionArgs {
-        mut function,
+        function,
         comma_and_arg,
     } = args;
-    let span = function.span();
-    let last_segment = function
-        .segments
-        .last_mut()
-        .ok_or_else(|| err_spanned!(span => "expected non-empty path"))?;
-
-    last_segment.ident = function_wrapper_ident(&last_segment.ident);
-
-    let output = if let Some((_, arg)) = comma_and_arg {
-        quote! { #function(#arg) }
+    if let Some((_, arg)) = comma_and_arg {
+        quote! { #function::wrap(#function::DEF, #arg) }
     } else {
-        quote! { &|arg| #function(arg) }
-    };
-    Ok(output)
+        quote! { &|arg| #function::wrap(#function::DEF, arg) }
+    }
 }
 
 pub fn wrap_pymodule_impl(mut module_path: syn::Path) -> syn::Result<TokenStream> {
@@ -58,10 +49,6 @@ pub fn wrap_pymodule_impl(mut module_path: syn::Path) -> syn::Result<TokenStream
     })
 }
 
-pub(crate) fn function_wrapper_ident(name: &Ident) -> Ident {
-    format_ident!("__pyo3_get_function_{}", name)
-}
-
 pub(crate) fn module_def_ident(name: &Ident) -> Ident {
     format_ident!("__PYO3_PYMODULE_DEF_{}", name.to_string().to_uppercase())
 }

pyo3-macros/src/lib.rs

@@ -166,7 +166,8 @@ pub fn pymethods(_: TokenStream, input: TokenStream) -> TokenStream {
 
 /// A proc macro used to expose Rust functions to Python.
 ///
-/// Functions annotated with `#[pyfunction]` can also be annotated with the following `#[pyo3]` options:
+/// Functions annotated with `#[pyfunction]` can also be annotated with the following `#[pyo3]`
+/// options:
 ///
 /// |  Annotation  |  Description |
 /// | :-  | :- |
@@ -176,6 +177,11 @@ pub fn pymethods(_: TokenStream, input: TokenStream) -> TokenStream {
 ///
 /// For more on exposing functions see the [function section of the guide][1].
 ///
+/// Due to technical limitations on how `#[pyfunction]` is implemented, a function marked
+/// `#[pyfunction]` cannot have a module with the same name in the same scope. (The
+/// `#[pyfunction]` implementation generates a hidden module with the same name containing
+/// metadata about the function, which is used by `wrap_pyfunction!`).
+///
 /// [1]: https://pyo3.rs/latest/function.html
 #[proc_macro_attribute]
 pub fn pyfunction(attr: TokenStream, input: TokenStream) -> TokenStream {
@@ -208,7 +214,7 @@ pub fn derive_from_py_object(item: TokenStream) -> TokenStream {
 #[proc_macro]
 pub fn wrap_pyfunction(input: TokenStream) -> TokenStream {
     let args = parse_macro_input!(input as WrapPyFunctionArgs);
-    wrap_pyfunction_impl(args).unwrap_or_compile_error().into()
+    wrap_pyfunction_impl(args).into()
 }
 
 /// Returns a function that takes a `Python` instance and returns a Python module.

src/derive_utils.rs

@@ -4,9 +4,7 @@
 
 //! Functionality for the code generated by the derive backend
 
-use crate::err::PyErr;
-use crate::types::PyModule;
-use crate::{PyCell, PyClass, Python};
+use crate::{types::PyModule, PyCell, PyClass, PyErr, Python};
 
 /// Utility trait to enable &PyClass as a pymethod/function argument
 #[doc(hidden)]

src/impl_.rs

@@ -13,5 +13,7 @@ pub(crate) mod not_send;
 #[doc(hidden)]
 pub mod pyclass;
 #[doc(hidden)]
+pub mod pyfunction;
+#[doc(hidden)]
 pub mod pymethods;
 pub mod pymodule;

src/impl_/pyfunction.rs

@@ -0,0 +1,14 @@
+use crate::{
+    class::methods::PyMethodDef, derive_utils::PyFunctionArguments, types::PyCFunction, PyResult,
+};
+
+pub trait PyFunctionDef {
+    const DEF: crate::PyMethodDef;
+}
+
+pub fn wrap_pyfunction<'a>(
+    method_def: PyMethodDef,
+    args: impl Into<PyFunctionArguments<'a>>,
+) -> PyResult<&'a PyCFunction> {
+    PyCFunction::internal_new(method_def, args.into())
+}

tests/test_pyfunction.rs

@@ -269,3 +269,29 @@ fn test_closure_counter() {
     py_assert!(py, counter_py, "counter_py() == 2");
     py_assert!(py, counter_py, "counter_py() == 3");
 }
+
+#[test]
+fn use_pyfunction() {
+    mod function_in_module {
+        use pyo3::prelude::*;
+
+        #[pyfunction]
+        pub fn foo(x: i32) -> i32 {
+            x
+        }
+    }
+
+    Python::with_gil(|py| {
+        use function_in_module::foo;
+
+        // check imported name can be wrapped
+        let f = wrap_pyfunction!(foo, py).unwrap();
+        assert_eq!(f.call1((5,)).unwrap().extract::<i32>().unwrap(), 5);
+        assert_eq!(f.call1((42,)).unwrap().extract::<i32>().unwrap(), 42);
+
+        // check path import can be wrapped
+        let f2 = wrap_pyfunction!(function_in_module::foo, py).unwrap();
+        assert_eq!(f2.call1((5,)).unwrap().extract::<i32>().unwrap(), 5);
+        assert_eq!(f2.call1((42,)).unwrap().extract::<i32>().unwrap(), 42);
+    })
+}