Expose non-impl-Trait iterator return types

src/data.rs

@@ -105,42 +105,44 @@ impl Fields {
         }
     }
 
-    /// Get an iterator over the fields of a struct or variant as [`Member`]s.
-    /// This iterator can be used to iterate over a named or unnamed struct or
-    /// variant's fields uniformly.
-    ///
-    /// # Example
-    ///
-    /// The following is a simplistic [`Clone`] derive for structs. (A more
-    /// complete implementation would additionally want to infer trait bounds on
-    /// the generic type parameters.)
-    ///
-    /// ```
-    /// # use quote::quote;
-    /// #
-    /// fn derive_clone(input: &syn::ItemStruct) -> proc_macro2::TokenStream {
-    ///     let ident = &input.ident;
-    ///     let members = input.fields.members();
-    ///     let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
-    ///     quote! {
-    ///         impl #impl_generics Clone for #ident #ty_generics #where_clause {
-    ///             fn clone(&self) -> Self {
-    ///                 Self {
-    ///                     #(#members: self.#members.clone()),*
-    ///                 }
-    ///             }
-    ///         }
-    ///     }
-    /// }
-    /// ```
-    ///
-    /// For structs with named fields, it produces an expression like `Self { a:
-    /// self.a.clone() }`. For structs with unnamed fields, `Self { 0:
-    /// self.0.clone() }`. And for unit structs, `Self {}`.
-    pub fn members(&self) -> impl Iterator<Item = Member> + Clone + '_ {
-        Members {
-            fields: self.iter(),
-            index: 0,
+    return_impl_trait! {
+        /// Get an iterator over the fields of a struct or variant as [`Member`]s.
+        /// This iterator can be used to iterate over a named or unnamed struct or
+        /// variant's fields uniformly.
+        ///
+        /// # Example
+        ///
+        /// The following is a simplistic [`Clone`] derive for structs. (A more
+        /// complete implementation would additionally want to infer trait bounds on
+        /// the generic type parameters.)
+        ///
+        /// ```
+        /// # use quote::quote;
+        /// #
+        /// fn derive_clone(input: &syn::ItemStruct) -> proc_macro2::TokenStream {
+        ///     let ident = &input.ident;
+        ///     let members = input.fields.members();
+        ///     let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+        ///     quote! {
+        ///         impl #impl_generics Clone for #ident #ty_generics #where_clause {
+        ///             fn clone(&self) -> Self {
+        ///                 Self {
+        ///                     #(#members: self.#members.clone()),*
+        ///                 }
+        ///             }
+        ///         }
+        ///     }
+        /// }
+        /// ```
+        ///
+        /// For structs with named fields, it produces an expression like `Self { a:
+        /// self.a.clone() }`. For structs with unnamed fields, `Self { 0:
+        /// self.0.clone() }`. And for unit structs, `Self {}`.
+        pub fn members(&self) -> impl Iterator<Item = Member> + Clone + '_ [Members] {
+            Members {
+                fields: self.iter(),
+                index: 0,
+            }
         }
     }
 }

src/generics.rs

@@ -103,34 +103,46 @@ impl Default for Generics {
 }
 
 impl Generics {
-    /// Iterator over the lifetime parameters in `self.params`.
-    pub fn lifetimes(&self) -> impl Iterator<Item = &LifetimeParam> {
-        Lifetimes(self.params.iter())
+    return_impl_trait! {
+        /// Iterator over the lifetime parameters in `self.params`.
+        pub fn lifetimes(&self) -> impl Iterator<Item = &LifetimeParam> [Lifetimes] {
+            Lifetimes(self.params.iter())
+        }
     }
 
-    /// Iterator over the lifetime parameters in `self.params`.
-    pub fn lifetimes_mut(&mut self) -> impl Iterator<Item = &mut LifetimeParam> {
-        LifetimesMut(self.params.iter_mut())
+    return_impl_trait! {
+        /// Iterator over the lifetime parameters in `self.params`.
+        pub fn lifetimes_mut(&mut self) -> impl Iterator<Item = &mut LifetimeParam> [LifetimesMut] {
+            LifetimesMut(self.params.iter_mut())
+        }
     }
 
-    /// Iterator over the type parameters in `self.params`.
-    pub fn type_params(&self) -> impl Iterator<Item = &TypeParam> {
-        TypeParams(self.params.iter())
+    return_impl_trait! {
+        /// Iterator over the type parameters in `self.params`.
+        pub fn type_params(&self) -> impl Iterator<Item = &TypeParam> [TypeParams] {
+            TypeParams(self.params.iter())
+        }
     }
 
-    /// Iterator over the type parameters in `self.params`.
-    pub fn type_params_mut(&mut self) -> impl Iterator<Item = &mut TypeParam> {
-        TypeParamsMut(self.params.iter_mut())
+    return_impl_trait! {
+        /// Iterator over the type parameters in `self.params`.
+        pub fn type_params_mut(&mut self) -> impl Iterator<Item = &mut TypeParam> [TypeParamsMut] {
+            TypeParamsMut(self.params.iter_mut())
+        }
     }
 
-    /// Iterator over the constant parameters in `self.params`.
-    pub fn const_params(&self) -> impl Iterator<Item = &ConstParam> {
-        ConstParams(self.params.iter())
+    return_impl_trait! {
+        /// Iterator over the constant parameters in `self.params`.
+        pub fn const_params(&self) -> impl Iterator<Item = &ConstParam> [ConstParams] {
+            ConstParams(self.params.iter())
+        }
     }
 
-    /// Iterator over the constant parameters in `self.params`.
-    pub fn const_params_mut(&mut self) -> impl Iterator<Item = &mut ConstParam> {
-        ConstParamsMut(self.params.iter_mut())
+    return_impl_trait! {
+        /// Iterator over the constant parameters in `self.params`.
+        pub fn const_params_mut(&mut self) -> impl Iterator<Item = &mut ConstParam> [ConstParamsMut] {
+            ConstParamsMut(self.params.iter_mut())
+        }
     }
 
     /// Initializes an empty `where`-clause if there is not one present already.

src/macros.rs

@@ -164,3 +164,19 @@ macro_rules! check_keyword_matches {
     (pub pub) => {};
     (struct struct) => {};
 }
+
+#[cfg(any(feature = "full", feature = "derive"))]
+macro_rules! return_impl_trait {
+    (
+        $(#[$attr:meta])*
+        $vis:vis fn $name:ident $args:tt -> $impl_trait:ty [$concrete:ty] $body:block
+    ) => {
+        #[cfg(not(docsrs))]
+        $(#[$attr])*
+        $vis fn $name $args -> $concrete $body
+
+        #[cfg(docsrs)]
+        $(#[$attr])*
+        $vis fn $name $args -> $impl_trait $body
+    };
+}