common: Introduce DisplayAmount

Introduce a version of `DecimalAmount` that has equality comparison so
it can be easily used in error types. See doc comments for more details.

common/src/primitives/decimal_amount.rs

@@ -188,6 +188,70 @@ pub enum ParseError {
     IntParse(#[from] std::num::ParseIntError),
 }
 
+/// Just like [DecimalAmount] but useful in error types, picking a different set of trade-offs.
+///
+/// While [DecimalAmount] is intended to be used as a type to serialize/deserialize amounts to/from
+/// a string, [DisplayAmount] is for printing only. It has an equality comparison (comparing the
+/// string representation). To prevent the result of the comparison from affecting subsequent
+/// [Amount] calculations, there is no easy way of converting `DisplayAmount` to `Amount`.
+///
+/// To further encourage debuggability, we only provide the `from_amount_full` constructor for
+/// converting from `Amount` while `from_amount_minimal` is omitted. The full variant keeps all the
+/// trailing zeros, making it possible to see the amount both in coin/token units and in atoms.
+///
+/// This is most useful in error types where we want to display the amount and subsequently compare
+/// the errors for equality in tests.
+#[derive(Clone, Copy)]
+pub struct DisplayAmount(DecimalAmount);
+
+impl DisplayAmount {
+    /// Convert from [DecimalAmount]
+    pub const fn from_decimal_amount(value: DecimalAmount) -> Self {
+        Self(value)
+    }
+
+    /// Convert from integer with no decimals
+    pub const fn from_uint_integral(number: u128) -> Self {
+        Self(DecimalAmount::from_uint_integral(number))
+    }
+
+    /// Convert from integer, interpreting the last N digits as the fractional part
+    pub const fn from_uint_decimal(mantissa: UnsignedIntType, decimals: u8) -> Self {
+        Self(DecimalAmount::from_uint_decimal(mantissa, decimals))
+    }
+
+    /// Convert from [Amount], keeping all decimal digits
+    pub const fn from_amount_full(amount: Amount, decimals: u8) -> Self {
+        Self(DecimalAmount::from_amount_full(amount, decimals))
+    }
+}
+
+impl std::cmp::PartialEq for DisplayAmount {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.is_same(&other.0)
+    }
+}
+
+impl std::cmp::Eq for DisplayAmount {}
+
+impl From<DecimalAmount> for DisplayAmount {
+    fn from(value: DecimalAmount) -> Self {
+        Self::from_decimal_amount(value)
+    }
+}
+
+impl std::fmt::Display for DisplayAmount {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+impl std::fmt::Debug for DisplayAmount {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

mempool/src/error/mod.rs

@@ -22,7 +22,7 @@ use thiserror::Error;
 
 use common::{
     chain::{GenBlock, Transaction},
-    primitives::{Id, H256},
+    primitives::{decimal_amount::DisplayAmount, Id, H256},
 };
 
 use crate::pool::fee::Fee;
@@ -77,12 +77,18 @@ pub enum MempoolPolicyError {
     TransactionFeeLowerThanConflictsWithDescendants,
     #[error("Underflow in computing transaction's additional fees.")]
     AdditionalFeesUnderflow,
-    #[error("Transaction does not pay sufficient fees to be relayed (tx_fee: {tx_fee:?}, min_relay_fee: {min_relay_fee:?}).")]
-    InsufficientFeesToRelay { tx_fee: Fee, min_relay_fee: Fee },
+    #[error("Transaction does not pay sufficient fees to be relayed (tx_fee: {tx_fee}, min_relay_fee: {min_relay_fee}).")]
+    InsufficientFeesToRelay {
+        tx_fee: DisplayAmount,
+        min_relay_fee: DisplayAmount,
+    },
     #[error("Replacement transaction does not pay enough for its bandwidth.")]
     InsufficientFeesToRelayRBF,
-    #[error("Rolling fee threshold not met.")]
-    RollingFeeThresholdNotMet { minimum_fee: Fee, tx_fee: Fee },
+    #[error("Rolling fee threshold not met (fee is {tx_fee}, minimum {minimum_fee}).")]
+    RollingFeeThresholdNotMet {
+        minimum_fee: DisplayAmount,
+        tx_fee: DisplayAmount,
+    },
     #[error("Overflow encountered while computing fee with ancestors")]
     AncestorFeeOverflow,
     #[error("Overflow encountered while updating ancestor fee.")]

mempool/src/pool/mod.rs

@@ -35,7 +35,7 @@ use common::{
         block::timestamp::BlockTimestamp, Block, ChainConfig, GenBlock, SignedTransaction,
         Transaction,
     },
-    primitives::{amount::Amount, time::Time, BlockHeight, Id},
+    primitives::{amount::Amount, decimal_amount::DisplayAmount, time::Time, BlockHeight, Id},
     time_getter::TimeGetter,
 };
 use logging::log;
@@ -529,14 +529,15 @@ impl<M: MemoryUsageEstimator> Mempool<M> {
     }
 
     fn pays_minimum_mempool_fee(&self, tx: &TxEntryWithFee) -> Result<(), MempoolPolicyError> {
+        let decimals = self.chain_config.coin_decimals();
         let tx_fee = tx.fee();
         let minimum_fee = self.get_update_minimum_mempool_fee(tx.transaction())?;
         log::debug!("pays_minimum_mempool_fee tx_fee = {tx_fee:?}, minimum_fee = {minimum_fee:?}");
         ensure!(
             tx_fee >= minimum_fee,
             MempoolPolicyError::RollingFeeThresholdNotMet {
-                minimum_fee,
-                tx_fee,
+                minimum_fee: DisplayAmount::from_amount_full(minimum_fee.into(), decimals),
+                tx_fee: DisplayAmount::from_amount_full(tx_fee.into(), decimals),
             }
         );
         Ok(())
@@ -558,14 +559,15 @@ impl<M: MemoryUsageEstimator> Mempool<M> {
     }
 
     fn pays_minimum_relay_fees(&self, tx: &TxEntryWithFee) -> Result<(), MempoolPolicyError> {
+        let decimals = self.chain_config.coin_decimals();
         let tx_fee = tx.fee();
         let min_relay_fee = self.get_minimum_relay_fee(tx.transaction())?;
         log::debug!("tx_fee: {:?}, min_relay_fee: {:?}", tx_fee, min_relay_fee);
         ensure!(
             tx_fee >= min_relay_fee,
             MempoolPolicyError::InsufficientFeesToRelay {
-                tx_fee,
-                min_relay_fee
+                tx_fee: DisplayAmount::from_amount_full(tx_fee.into(), decimals),
+                min_relay_fee: DisplayAmount::from_amount_full(min_relay_fee.into(), decimals),
             }
         );
         Ok(())