Define a constant `EphemeralParameters::NONE` instead of deriving `Default`.

Signed-off-by: Daira-Emma Hopwood <daira@jacaranda.org>

zcash_client_backend/CHANGELOG.md

@@ -70,7 +70,8 @@ funds to those addresses. See [ZIP 320](https://zips.z.cash/zip-0320) for detail
     `&EphemeralParameters` parameter when the "transparent-inputs" feature is
     enabled. This can be used to specify whether the change memo should be
     ignored, and the amounts of additional transparent P2PKH inputs and
-    outputs. Passing `&Default::default()` will retain the previous behaviour.
+    outputs. Passing `&EphemeralParameters::NONE` will retain the previous
+    behaviour.
 - `zcash_client_backend::input_selection::GreedyInputSelectorError` has a
   new variant `UnsupportedTexAddress`.
 - `zcash_client_backend::proto::ProposalDecodingError` has a new variant

zcash_client_backend/src/data_api/wallet/input_selection.rs

@@ -462,7 +462,7 @@ where
         #[cfg(feature = "transparent-inputs")]
         let (ephemeral_parameters, tr1_balance_opt) = {
             if tr1_transparent_outputs.is_empty() {
-                (Default::default(), None)
+                (EphemeralParameters::NONE, None)
             } else {
                 // The ephemeral input going into transaction 1 must be able to pay that
                 // transaction's fee, as well as the TEX address payments.
@@ -772,7 +772,7 @@ where
             &orchard_fees::EmptyBundleView,
             &self.dust_output_policy,
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         let balance = match trial_balance {
@@ -791,7 +791,7 @@ where
                     &orchard_fees::EmptyBundleView,
                     &self.dust_output_policy,
                     #[cfg(feature = "transparent-inputs")]
-                    &Default::default(),
+                    &EphemeralParameters::NONE,
                 )?
             }
             Err(other) => {

zcash_client_backend/src/fees.rs

@@ -334,7 +334,7 @@ impl Default for DustOutputPolicy {
 /// and fees are computed that are relevant to transactions using ephemeral
 /// transparent outputs.
 #[cfg(feature = "transparent-inputs")]
-#[derive(Clone, Debug, Default, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub struct EphemeralParameters {
     ignore_change_memo: bool,
     ephemeral_input_amount: Option<NonNegativeAmount>,
@@ -343,6 +343,14 @@ pub struct EphemeralParameters {
 
 #[cfg(feature = "transparent-inputs")]
 impl EphemeralParameters {
+    /// An `EphemeralParameters` indicating no use of ephemeral inputs
+    /// or outputs. It has:
+    ///
+    /// * `ignore_change_memo: false`,
+    /// * `ephemeral_input_amount: None`,
+    /// * `ephemeral_output_amount: None`.
+    pub const NONE: Self = Self::new(false, None, None);
+
     /// Returns an `EphemeralParameters` with the following parameters:
     ///
     /// * `ignore_change_memo`: `true` if the change memo should be
@@ -352,7 +360,7 @@ impl EphemeralParameters {
     ///   additional P2PKH input of the given amount.
     /// * `ephemeral_output_amount`: specifies that there will be an
     ///   additional P2PKH output of the given amount.
-    pub fn new(
+    pub const fn new(
         ignore_change_memo: bool,
         ephemeral_input_amount: Option<NonNegativeAmount>,
         ephemeral_output_amount: Option<NonNegativeAmount>,

zcash_client_backend/src/fees/fixed.rs

@@ -109,6 +109,9 @@ mod tests {
         ShieldedProtocol,
     };
 
+    #[cfg(feature = "transparent-inputs")]
+    use crate::fees::EphemeralParameters;
+
     #[cfg(feature = "orchard")]
     use crate::fees::orchard as orchard_fees;
 
@@ -141,7 +144,7 @@ mod tests {
             &orchard_fees::EmptyBundleView,
             &DustOutputPolicy::default(),
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         assert_matches!(
@@ -188,7 +191,7 @@ mod tests {
             &orchard_fees::EmptyBundleView,
             &DustOutputPolicy::default(),
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         assert_matches!(

zcash_client_backend/src/fees/zip317.rs

@@ -116,6 +116,9 @@ mod tests {
         ShieldedProtocol,
     };
 
+    #[cfg(feature = "transparent-inputs")]
+    use crate::fees::EphemeralParameters;
+
     #[cfg(feature = "orchard")]
     use {
         crate::data_api::wallet::input_selection::OrchardPayment,
@@ -152,7 +155,7 @@ mod tests {
             &orchard_fees::EmptyBundleView,
             &DustOutputPolicy::default(),
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         assert_matches!(
@@ -197,7 +200,7 @@ mod tests {
             ),
             &DustOutputPolicy::default(),
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         assert_matches!(
@@ -251,7 +254,7 @@ mod tests {
             &orchard_fees::EmptyBundleView,
             dust_output_policy,
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         assert_matches!(
@@ -296,7 +299,7 @@ mod tests {
             &orchard_fees::EmptyBundleView,
             &DustOutputPolicy::default(),
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         assert_matches!(
@@ -341,7 +344,7 @@ mod tests {
             &orchard_fees::EmptyBundleView,
             &DustOutputPolicy::default(),
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         assert_matches!(
@@ -392,7 +395,7 @@ mod tests {
                 Some(NonNegativeAmount::const_from_u64(1000)),
             ),
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         assert_matches!(
@@ -454,7 +457,7 @@ mod tests {
             &orchard_fees::EmptyBundleView,
             dust_output_policy,
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         assert_matches!(
@@ -506,7 +509,7 @@ mod tests {
             &orchard_fees::EmptyBundleView,
             &DustOutputPolicy::default(),
             #[cfg(feature = "transparent-inputs")]
-            &Default::default(),
+            &EphemeralParameters::NONE,
         );
 
         // We will get an error here, because the dust input isn't free to add