syn: add EnumKind type and Items<Variants>::enum_kind method

Author: dr-orlovsky

syn/src/data.rs

@@ -54,6 +54,12 @@ pub enum FieldKind {
     Unnamed,
 }
 
+#[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
+pub enum EnumKind {
+    Primitive,
+    Associated,
+}
+
 impl Fields {
     pub fn is_unit(&self) -> bool { matches!(self, Fields::Unit) }
 
@@ -90,6 +96,16 @@ impl<'a, E: Element> IntoIterator for &'a Items<E> {
     fn into_iter(self) -> Self::IntoIter { self.0.iter() }
 }
 
+impl Items<Variant> {
+    pub fn enum_kind(&self) -> EnumKind {
+        if self.iter().all(|var| var.fields.is_unit()) {
+            EnumKind::Primitive
+        } else {
+            EnumKind::Associated
+        }
+    }
+}
+
 #[derive(Clone)]
 pub struct NamedField {
     pub name: Ident,

syn/src/lib.rs

@@ -51,8 +51,8 @@ mod data;
 pub use attr::{Attr, ExtractAttr, ParametrizedAttr, SingularAttr};
 pub use cls::{LiteralClass, TypeClass, ValueClass};
 pub use data::{
-    DataInner, DataType, DeriveInner, Element, Field, FieldKind, Fields, Items, NamedField, Scope,
-    Variant, Vis,
+    DataInner, DataType, DeriveInner, Element, EnumKind, Field, FieldKind, Fields, Items,
+    NamedField, Scope, Variant, Vis,
 };
 pub use error::Error;
 pub use parsers::{MetaArg, MetaArgList, MetaArgNameValue};