add enum annotation definitions (#27)

src/main/scala/firrtl2/annotations/EnumAnnotations.scala

@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package firrtl2.annotations
+
+/** An annotation for strong enum instances that are ''not'' inside of Vecs
+  *
+  * @param target the enum instance being annotated
+  * @param enumTypeName the name of the enum's type (e.g. ''"mypackage.MyEnum"'')
+  */
+case class EnumComponentAnnotation(target: Named, enumTypeName: String) extends SingleTargetAnnotation[Named] {
+  def duplicate(n: Named): EnumComponentAnnotation = this.copy(target = n)
+}
+
+/** An annotation for Vecs of strong enums.
+  *
+  * The ''fields'' parameter deserves special attention, since it may be difficult to understand. Suppose you create a the following Vec:
+  *
+  *               {{{
+  *               VecInit(new Bundle {
+  *                 val e = MyEnum()
+  *                 val b = new Bundle {
+  *                   val inner_e = MyEnum()
+  *                 }
+  *                 val v = Vec(3, MyEnum())
+  *               }
+  *               }}}
+  *
+  *               Then, the ''fields'' parameter will be: ''Seq(Seq("e"), Seq("b", "inner_e"), Seq("v"))''. Note that for any Vec that doesn't contain Bundles, this field will simply be an empty Seq.
+  *
+  * @param target the Vec being annotated
+  * @param typeName the name of the enum's type (e.g. ''"mypackage.MyEnum"'')
+  * @param fields a list of all chains of elements leading from the Vec instance to its inner enum fields.
+  */
+case class EnumVecAnnotation(target: Named, typeName: String, fields: Seq[Seq[String]])
+    extends SingleTargetAnnotation[Named] {
+  def duplicate(n: Named): EnumVecAnnotation = this.copy(target = n)
+}
+
+/** An annotation for enum types (rather than enum ''instances'').
+  *
+  * @param typeName the name of the enum's type (e.g. ''"mypackage.MyEnum"'')
+  * @param definition a map describing which integer values correspond to which enum names
+  */
+case class EnumDefAnnotation(typeName: String, definition: Map[String, BigInt]) extends NoTargetAnnotation