rust: pin-init: internal: extract utility code to new module

Create a new `util.rs` to host utility code that are generic and can be
shared by multiple macros.

Link: https://patch.msgid.link/20260904-tuple-struct-v1-1-72c50bd037fd@garyguo.net
Signed-off-by: Gary Guo <gary@garyguo.net>

rust/pin-init/internal/src/lib.rs

@@ -18,6 +18,7 @@
 mod init;
 mod pin_data;
 mod pinned_drop;
+mod util;
 mod zeroable;
 
 #[proc_macro_attribute]

rust/pin-init/internal/src/pin_data.rs

@@ -10,7 +10,10 @@
     Field, Fields, Generics, Ident, Item, PathSegment, Type, TypePath, Visibility, WhereClause,
 };
 
-use crate::diagnostics::{DiagCtxt, ErrorGuaranteed};
+use crate::{
+    diagnostics::{DiagCtxt, ErrorGuaranteed},
+    util::*,
+};
 
 pub(crate) mod kw {
     syn::custom_keyword!(PinnedDrop);
@@ -81,21 +84,11 @@ pub(crate) fn pin_data(
     //
     // We need to perform this after parsing so we can reliably detect field cfgs.
     for (field_idx, field) in struct_.fields.iter_mut().enumerate() {
-        let cfg: Vec<_> = field
-            .attrs
-            .iter()
-            .filter(|a| a.path().is_ident("cfg"))
-            .map(|a| {
-                a.parse_args::<TokenStream>()
-                    .expect("parse as token stream cannot fail")
-            })
-            .collect();
-
+        let cfg = field.attrs.extract_cfg_attrs();
         if cfg.is_empty() {
             continue;
         }
 
-        field.attrs.retain(|a| !a.path().is_ident("cfg"));
         let cfg_true_struct = quote!(#struct_);
 
         let punctuated = match &mut struct_.fields {

rust/pin-init/internal/src/util.rs

@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use proc_macro2::TokenStream;
+use syn::Attribute;
+
+pub(crate) trait AttrListExt {
+    fn extract_cfg_attrs(&mut self) -> Vec<TokenStream>;
+}
+
+impl AttrListExt for Vec<Attribute> {
+    fn extract_cfg_attrs(&mut self) -> Vec<TokenStream> {
+        let cfg: Vec<_> = self
+            .iter()
+            .filter(|a| a.path().is_ident("cfg"))
+            .map(|a| {
+                a.parse_args::<TokenStream>()
+                    .expect("parse as token stream cannot fail")
+            })
+            .collect();
+
+        if !cfg.is_empty() {
+            self.retain(|a| !a.path().is_ident("cfg"));
+        }
+
+        cfg
+    }
+}