Expose num_actions as a method on PaddingRule

src/builder.rs

@@ -46,6 +46,25 @@ impl PaddingRule {
     /// The default padding rule, which ensures that the constructed bundle will contain at least 2
     /// actions if any genuine Orchard spends or outputs are requested.
     pub const DEFAULT: PaddingRule = PaddingRule::PadTo(MIN_ACTIONS);
+
+    /// Returns the number of logical actions that the builder will add to the bundle
+    /// as a consequence of this padding rule, given the specified number of spends
+    /// and recipients.
+    pub fn num_actions(&self, num_spends: usize, num_recipients: usize) -> usize {
+        let num_real_actions = core::cmp::max(num_spends, num_recipients);
+
+        match self {
+            PaddingRule::Require(n) => core::cmp::max(num_real_actions, *n),
+            PaddingRule::PadTo(n) => {
+                if num_real_actions == 0 {
+                    0
+                } else {
+                    core::cmp::max(num_real_actions, *n)
+                }
+            }
+            PaddingRule::None => num_real_actions,
+        }
+    }
 }
 
 /// An error type for the kinds of errors that can occur during bundle construction.
@@ -414,19 +433,9 @@ impl Builder {
     ) -> Result<Bundle<InProgress<Unproven, Unauthorized>, V>, BuildError> {
         let num_real_spends = self.spends.len();
         let num_real_recipients = self.recipients.len();
-        let num_real_actions = core::cmp::max(num_real_spends, num_real_recipients);
-
-        let num_actions = match self.padding_rule {
-            PaddingRule::Require(n) => core::cmp::max(num_real_actions, n),
-            PaddingRule::PadTo(n) => {
-                if num_real_actions == 0 {
-                    0
-                } else {
-                    core::cmp::max(num_real_actions, n)
-                }
-            }
-            PaddingRule::None => num_real_actions,
-        };
+        let num_actions = self
+            .padding_rule
+            .num_actions(num_real_spends, num_real_recipients);
 
         // Pair up the spends and recipients, extending with dummy values as necessary.
         let pre_actions: Vec<_> = {