Allow storing V with #[derive(Enum)]

enum-map reserves __EnumMapInternalV for this purpose. This
is not a part of stable API, and it's only necessary due
to not having stable def_site hygiene.

Author: sugar700

enum-map-derive/src/derive_enum.rs

@@ -37,7 +37,7 @@ impl EnumGenerator {
         quote! {
             #[automatically_derived]
             impl ::enum_map::Enum for #name {
-                type Array<V> = [V; #length];
+                type Array<__EnumMapInternalV> = [__EnumMapInternalV; #length];
 
                 #[inline]
                 fn from_usize(value: ::enum_map::usize) -> Self {

enum-map-derive/src/derive_struct.rs

@@ -102,7 +102,7 @@ impl StructGenerator {
         quote! {
             #[automatically_derived]
             impl ::enum_map::Enum for #name {
-                type Array<V> = [V; #length];
+                type Array<__EnumMapInternalV> = [__EnumMapInternalV; #length];
 
                 #[inline]
                 fn from_usize(value: ::enum_map::usize) -> Self {

enum-map/tests/test.rs

@@ -639,3 +639,12 @@ fn usize_override() {
         B,
     }
 }
+
+#[derive(Enum)]
+enum V {
+    V,
+}
+#[derive(Enum)]
+struct StructureCanHoldV {
+    v: V,
+}