addressing feedback

Author: ZuseZ4

compiler/rustc_ast/src/expand/autodiff_attrs.rs

@@ -69,6 +69,12 @@ pub enum DiffActivity {
     /// length of a slice/vec. This is used for safety checks on slices.
     FakeActivitySize,
 }
+
+impl DiffActivity {
+    pub fn is_dual_or_const(&self) -> bool {
+        use DiffActivity::*;
+        matches!(self, |Dual | DualOnly | Dualv | DualvOnly | Const)
+    }
 /// We generate one of these structs for each `#[autodiff(...)]` attribute.
 #[derive(Clone, Eq, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
 pub struct AutoDiffItem {
@@ -140,11 +146,7 @@ pub fn valid_ret_activity(mode: DiffMode, activity: DiffActivity) -> bool {
         DiffMode::Error => false,
         DiffMode::Source => false,
         DiffMode::Forward => {
-            activity == DiffActivity::Dual
-                || activity == DiffActivity::Dualv
-                || activity == DiffActivity::DualOnly
-                || activity == DiffActivity::DualvOnly
-                || activity == DiffActivity::Const
+            activity.is_dual_or_const()
         }
         DiffMode::Reverse => {
             activity == DiffActivity::Const
@@ -163,10 +165,8 @@ pub fn valid_ret_activity(mode: DiffMode, activity: DiffActivity) -> bool {
 pub fn valid_ty_for_activity(ty: &P<Ty>, activity: DiffActivity) -> bool {
     use DiffActivity::*;
     // It's always allowed to mark something as Const, since we won't compute derivatives wrt. it.
-    if matches!(activity, Const) {
-        return true;
-    }
-    if matches!(activity, Dual | DualOnly | Dualv | DualvOnly) {
+    // Dual variants also support all types.
+    if activity.is_dual_or_const() {
         return true;
     }
     // FIXME(ZuseZ4) We should make this more robust to also
@@ -183,7 +183,7 @@ pub fn valid_input_activity(mode: DiffMode, activity: DiffActivity) -> bool {
         DiffMode::Error => false,
         DiffMode::Source => false,
         DiffMode::Forward => {
-            matches!(activity, Dual | DualOnly | Dualv | DualvOnly | Const)
+            activity.is_dual_or_const()
         }
         DiffMode::Reverse => {
             matches!(activity, Active | ActiveOnly | Duplicated | DuplicatedOnly | Const)