allow custom derives on enums

Custom derives are just as useful on enums as they are on structs; not
supporting this was an oversight.

Adds a test that will fail to compile if the custom derive doesn't work
on enums. This test fails without the codegen fix.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/codegen/mod.rs b/src/codegen/mod.rs
index 69dde2c5..b703a106 100644
--- a/src/codegen/mod.rs
+++ b/src/codegen/mod.rs
@@ -3014,6 +3014,16 @@ impl CodeGenerator for Enum {
                     derives.push(derive);
                 }
             }
+
+            // The custom derives callback may return a list of derive attributes;
+            // add them to the end of the list.
+            let custom_derives;
+            if let Some(cb) = &ctx.options().parse_callbacks {
+                custom_derives = cb.add_derives(&name);
+                // In most cases this will be a no-op, since custom_derives will be empty.
+                derives.extend(custom_derives.iter().map(|s| s.as_str()));
+            };
+
             attrs.push(attributes::derives(&derives));
         }