From f3603a0a483448c71f1811786257d070733540bf Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Mon, 1 Jul 2024 17:54:50 -0400
Subject: [PATCH] Avoid generating functions that are only ever const evaluated
 with declarative modules (#4297)

Refs #4286
---
 newsfragments/4297.fixed.md       |  1 +
 pyo3-macros-backend/src/module.rs | 34 ++++++++++++++-----------------
 2 files changed, 16 insertions(+), 19 deletions(-)
 create mode 100644 newsfragments/4297.fixed.md

diff --git a/newsfragments/4297.fixed.md b/newsfragments/4297.fixed.md
new file mode 100644
index 00000000000..18cfd93756f
--- /dev/null
+++ b/newsfragments/4297.fixed.md
@@ -0,0 +1 @@
+stop generating code that will never be covered with declarative modules
diff --git a/pyo3-macros-backend/src/module.rs b/pyo3-macros-backend/src/module.rs
index 39240aba7e8..4ce3023cbb4 100644
--- a/pyo3-macros-backend/src/module.rs
+++ b/pyo3-macros-backend/src/module.rs
@@ -286,7 +286,18 @@ pub fn pymodule_module_impl(mut module: syn::ItemMod) -> Result<TokenStream> {
         }
     }
 
-    let initialization = module_initialization(&name, ctx);
+    let module_def = quote! {{
+        use #pyo3_path::impl_::pymodule as impl_;
+        const INITIALIZER: impl_::ModuleInitializer = impl_::ModuleInitializer(__pyo3_pymodule);
+        unsafe {
+           impl_::ModuleDef::new(
+                __PYO3_NAME,
+                #doc,
+                INITIALIZER
+            )
+        }
+    }};
+    let initialization = module_initialization(&name, ctx, module_def);
     Ok(quote!(
         #(#attrs)*
         #vis mod #ident {
@@ -294,21 +305,6 @@ pub fn pymodule_module_impl(mut module: syn::ItemMod) -> Result<TokenStream> {
 
             #initialization
 
-            #[allow(unknown_lints, non_local_definitions)]
-            impl MakeDef {
-                const fn make_def() -> #pyo3_path::impl_::pymodule::ModuleDef {
-                    use #pyo3_path::impl_::pymodule as impl_;
-                    const INITIALIZER: impl_::ModuleInitializer = impl_::ModuleInitializer(__pyo3_pymodule);
-                    unsafe {
-                       impl_::ModuleDef::new(
-                            __PYO3_NAME,
-                            #doc,
-                            INITIALIZER
-                        )
-                    }
-                }
-            }
-
             fn __pyo3_pymodule(module: &#pyo3_path::Bound<'_, #pyo3_path::types::PyModule>) -> #pyo3_path::PyResult<()> {
                 use #pyo3_path::impl_::pymodule::PyAddToModule;
                 #(
@@ -335,7 +331,7 @@ pub fn pymodule_function_impl(mut function: syn::ItemFn) -> Result<TokenStream>
     let vis = &function.vis;
     let doc = get_doc(&function.attrs, None, ctx);
 
-    let initialization = module_initialization(&name, ctx);
+    let initialization = module_initialization(&name, ctx, quote! { MakeDef::make_def() });
 
     // Module function called with optional Python<'_> marker as first arg, followed by the module.
     let mut module_args = Vec::new();
@@ -400,7 +396,7 @@ pub fn pymodule_function_impl(mut function: syn::ItemFn) -> Result<TokenStream>
     })
 }
 
-fn module_initialization(name: &syn::Ident, ctx: &Ctx) -> TokenStream {
+fn module_initialization(name: &syn::Ident, ctx: &Ctx, module_def: TokenStream) -> TokenStream {
     let Ctx { pyo3_path, .. } = ctx;
     let pyinit_symbol = format!("PyInit_{}", name);
     let name = name.to_string();
@@ -412,7 +408,7 @@ fn module_initialization(name: &syn::Ident, ctx: &Ctx) -> TokenStream {
 
         pub(super) struct MakeDef;
         #[doc(hidden)]
-        pub static _PYO3_DEF: #pyo3_path::impl_::pymodule::ModuleDef = MakeDef::make_def();
+        pub static _PYO3_DEF: #pyo3_path::impl_::pymodule::ModuleDef = #module_def;
 
         /// This autogenerated function is called by the python interpreter when importing
         /// the module.