internal: pin_data: add struct to record field info

Introduce `FieldInfo` struct to encapsulate field and other relevant data,
instead of carrying a pair of `(pinned, field)` in all places. This allows
us to add more information to the struct in the future.

Signed-off-by: Mohamad Alsadhan <mo@sdhn.cc>
Co-developed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Gary Guo <gary@garyguo.net>

Author: mqqz

internal/src/pin_data.rs

@@ -35,6 +35,11 @@ impl Parse for Args {
     }
 }
 
+struct FieldInfo<'a> {
+    field: &'a Field,
+    pinned: bool,
+}
+
 pub(crate) fn pin_data(
     args: Args,
     input: Item,
@@ -73,24 +78,30 @@ pub(crate) fn pin_data(
     replacer.visit_generics_mut(&mut struct_.generics);
     replacer.visit_fields_mut(&mut struct_.fields);
 
-    let fields: Vec<(bool, &Field)> = struct_
+    let fields: Vec<FieldInfo<'_>> = struct_
         .fields
         .iter_mut()
         .map(|field| {
             let len = field.attrs.len();
             field.attrs.retain(|a| !a.path().is_ident("pin"));
-            (len != field.attrs.len(), &*field)
+            let pinned = len != field.attrs.len();
+
+            FieldInfo {
+                field: &*field,
+                pinned,
+            }
         })
         .collect();
 
-    for (pinned, field) in &fields {
-        if !pinned && is_phantom_pinned(&field.ty) {
+    for field in &fields {
+        let ident = field.field.ident.as_ref().unwrap();
+
+        if !field.pinned && is_phantom_pinned(&field.field.ty) {
             dcx.warn(
-                field,
+                field.field,
                 format!(
-                    "The field `{}` of type `PhantomPinned` only has an effect \
+                    "The field `{ident}` of type `PhantomPinned` only has an effect \
                     if it has the `#[pin]` attribute",
-                    field.ident.as_ref().unwrap(),
                 ),
             );
         }
@@ -143,7 +154,7 @@ fn is_phantom_pinned(ty: &Type) -> bool {
 fn generate_unpin_impl(
     ident: &Ident,
     generics: &Generics,
-    fields: &[(bool, &Field)],
+    fields: &[FieldInfo<'_>],
 ) -> TokenStream {
     let (_, ty_generics, _) = generics.split_for_impl();
     let mut generics_with_pin_lt = generics.clone();
@@ -160,7 +171,7 @@ fn generate_unpin_impl(
     else {
         unreachable!()
     };
-    let pinned_fields = fields.iter().filter_map(|(b, f)| b.then_some(f));
+    let pinned_fields = fields.iter().filter(|f| f.pinned).map(|f| f.field);
     quote! {
         // This struct will be used for the unpin analysis. It is needed, because only structurally
         // pinned fields are relevant whether the struct should implement `Unpin`.
@@ -238,7 +249,7 @@ fn generate_projections(
     vis: &Visibility,
     ident: &Ident,
     generics: &Generics,
-    fields: &[(bool, &Field)],
+    fields: &[FieldInfo<'_>],
 ) -> TokenStream {
     let (impl_generics, ty_generics, _) = generics.split_for_impl();
     let mut generics_with_pin_lt = generics.clone();
@@ -249,21 +260,21 @@ fn generate_projections(
 
     let (fields_decl, fields_proj): (Vec<_>, Vec<_>) = fields
         .iter()
-        .map(|(pinned, field)| {
+        .map(|field| {
             let Field {
                 vis,
                 ident,
                 ty,
                 attrs,
                 ..
-            } = field;
+            } = &field.field;
 
             let mut no_doc_attrs = attrs.clone();
             no_doc_attrs.retain(|a| !a.path().is_ident("doc"));
             let ident = ident
                 .as_ref()
                 .expect("only structs with named fields are supported");
-            if *pinned {
+            if field.pinned {
                 (
                     quote!(
                         #(#attrs)*
@@ -291,12 +302,12 @@ fn generate_projections(
         .collect();
     let structurally_pinned_fields_docs = fields
         .iter()
-        .filter_map(|(pinned, field)| pinned.then_some(field))
-        .map(|Field { ident, .. }| format!(" - `{}`", ident.as_ref().unwrap()));
+        .filter(|f| f.pinned)
+        .map(|f| format!(" - `{}`", f.field.ident.as_ref().unwrap()));
     let not_structurally_pinned_fields_docs = fields
         .iter()
-        .filter_map(|(pinned, field)| (!pinned).then_some(field))
-        .map(|Field { ident, .. }| format!(" - `{}`", ident.as_ref().unwrap()));
+        .filter(|f| !f.pinned)
+        .map(|f| format!(" - `{}`", f.field.ident.as_ref().unwrap()));
     let docs = format!(" Pin-projections of [`{ident}`]");
     quote! {
         #[doc = #docs]
@@ -338,7 +349,7 @@ fn generate_the_pin_data(
     vis: &Visibility,
     struct_name: &Ident,
     generics: &Generics,
-    fields: &[(bool, &Field)],
+    fields: &[FieldInfo<'_>],
 ) -> TokenStream {
     let (impl_generics, ty_generics, whr) = generics.split_for_impl();
 
@@ -349,20 +360,20 @@ fn generate_the_pin_data(
     // The functions are `unsafe` to prevent accidentally calling them.
     let field_accessors = fields
         .iter()
-        .map(|(pinned, field)| {
+        .map(|f| {
             let Field {
                 vis,
                 ident,
                 ty,
                 attrs,
                 ..
-            } = field;
+            } = f.field;
 
             let field_name = ident
                 .as_ref()
                 .expect("only structs with named fields are supported");
             let project_ident = format_ident!("__project_{field_name}");
-            let (init_ty, init_fn, project_ty, project_body, pin_safety) = if *pinned {
+            let (init_ty, init_fn, project_ty, project_body, pin_safety) = if f.pinned {
                 (
                     quote!(PinInit),
                     quote!(__pinned_init),