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Properly add link attributes to extern static pointer bindings #44

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Properly add link attributes to extern static pointer bindings #44

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66 changes: 34 additions & 32 deletions Cargo.lock
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2 changes: 2 additions & 0 deletions Modules/cpython-sys/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -7,4 +7,6 @@ edition = "2024"

[build-dependencies]
bindgen = "0.72.1"
prettyplease = "0.2.37"
shlex = "1.3"
syn = { version = "2.0.110", features = ["full", "parsing"] }
56 changes: 14 additions & 42 deletions Modules/cpython-sys/build.rs
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Expand Up @@ -324,52 +324,24 @@ fn patch_windows_imported_pointer_globals(bindings: String, dll_name: &str) -> S
// The fix: annotate pointer-valued extern statics with `raw-dylib` on
// Windows so Rust generates the import thunk itself and handles the IAT
// indirection correctly — two loads, matching `__declspec(dllimport)`.
let lines: Vec<_> = bindings.lines().collect();
let mut patched = String::with_capacity(bindings.len());
let mut index = 0;

while index < lines.len() {
if lines[index] == "unsafe extern \"C\" {"
&& lines
.get(index + 1)
.and_then(|l| parse_pointer_static_decl(l))
.is_some()
&& lines.get(index + 2).is_some_and(|l| l.trim() == "}")
{
patched.push_str(&format!(
"#[cfg_attr(windows, link(name = \"{dll_name}\", kind = \"raw-dylib\"))]\n"
));
// Keep the original extern block unchanged.
for i in index..index + 3 {
patched.push_str(lines[i]);
patched.push('\n');
}
index += 3;
let mut file = syn::parse_file(&bindings).expect("bindgen emitted invalid Rust");

for item in &mut file.items {
let syn::Item::ForeignMod(foreign_mod) = item else {
continue;
};
let [syn::ForeignItem::Static(static_item)] = foreign_mod.items.as_slice() else {

@davidhewitt davidhewitt Aug 10, 2026

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Is it expected that these extern blocks have a single item only?

@emmatyping emmatyping Aug 10, 2026

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Yes, bindgen will emit one extern block per global, e.g. (taken from a generated c_api.rs):

unsafe extern "C" {
    pub static mut PyLong_Type: PyTypeObject;
}
unsafe extern "C" {
    pub static mut PyBool_Type: PyTypeObject;
}

I'll add a comment because this is somewhat load bearing on how bindgen generates extern data from C.

continue;
};
if !matches!(*static_item.ty, syn::Type::Ptr(_)) {
continue;
}

patched.push_str(lines[index]);
patched.push('\n');
index += 1;
}

patched
}

fn parse_pointer_static_decl(line: &str) -> Option<(&str, bool, &str)> {
let mut decl = line.trim().strip_prefix("pub static ")?;
let is_mut = decl.starts_with("mut ");
if is_mut {
decl = decl.strip_prefix("mut ")?;
}

let (name, ty) = decl.split_once(':')?;
let ty = ty.trim().strip_suffix(';')?;
if !ty.starts_with('*') {
return None;
foreign_mod.attrs.push(syn::parse_quote!(
#[cfg_attr(windows, link(name = #dll_name, kind = "raw-dylib"))]
));
}

Some((name.trim(), is_mut, ty))
prettyplease::unparse(&file)
}

fn add_target_clang_args(
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