Fix amount whole bitcoin constructors

tcharding · tcharding · commit ef927092f6df · 2025-03-03T04:53:02.000+11:00
I royally botched the recent effort to make const amount constructors
use a smaller type. I left in an  unnecessary panic and forgot to do
both of them.

Note these function return values will change again very shortly when we
start enforcing the MAX_MONEY invariant. However the 64 to 32 bit change
is unrelated to that and is easier to review if done separately.

Whole bitcoin can non in any sane environment be greater than 21,000,000
which fits in 32 bits so we can take a 32 bit integer in the whole
bitcoin constructors without loss of utility. Doing so removes the
potential panic.

This is a breaking API change. We elect not to deprecate because we want
to keep the same function names.
diff --git a/units/src/amount/signed.rs b/units/src/amount/signed.rs
@@ -121,29 +121,19 @@ impl SignedAmount {
     }
 
     /// Converts from a value expressing a whole number of bitcoin to a [`SignedAmount`].
-    ///
-    /// # Errors
-    ///
-    /// The function errors if the argument multiplied by the number of sats
-    /// per bitcoin overflows an `i64` type.
-    pub fn from_int_btc<T: Into<i64>>(whole_bitcoin: T) -> Result<SignedAmount, OutOfRangeError> {
-        match whole_bitcoin.into().checked_mul(100_000_000) {
-            Some(amount) => Ok(Self::from_sat(amount)),
-            None => Err(OutOfRangeError { is_signed: true, is_greater_than_max: true }),
-        }
+    #[allow(clippy::missing_panics_doc)]
+    pub fn from_int_btc<T: Into<i32>>(whole_bitcoin: T) -> SignedAmount {
+        SignedAmount::from_int_btc_const(whole_bitcoin.into())
     }
 
     /// Converts from a value expressing a whole number of bitcoin to a [`SignedAmount`]
     /// in const context.
-    ///
-    /// # Panics
-    ///
-    /// The function panics if the argument multiplied by the number of sats
-    /// per bitcoin overflows an `i64` type.
-    pub const fn from_int_btc_const(whole_bitcoin: i64) -> SignedAmount {
-        match whole_bitcoin.checked_mul(100_000_000) {
+    #[allow(clippy::missing_panics_doc)]
+    pub const fn from_int_btc_const(whole_bitcoin: i32) -> SignedAmount {
+        let btc = whole_bitcoin as i64; // Can't call `into` in const context.
+        match btc.checked_mul(100_000_000) {
             Some(amount) => SignedAmount::from_sat(amount),
-            None => panic!("checked_mul overflowed"),
+            None => panic!("cannot overflow in i64"),
         }
     }
 
diff --git a/units/src/amount/unsigned.rs b/units/src/amount/unsigned.rs
@@ -122,30 +122,19 @@ impl Amount {
     }
 
     /// Converts from a value expressing a whole number of bitcoin to an [`Amount`].
-    ///
-    /// # Errors
-    ///
-    /// The function errors if the argument multiplied by the number of sats
-    /// per bitcoin overflows a `u64` type.
-    pub fn from_int_btc<T: Into<u64>>(whole_bitcoin: T) -> Result<Amount, OutOfRangeError> {
-        match whole_bitcoin.into().checked_mul(100_000_000) {
-            Some(amount) => Ok(Self::from_sat(amount)),
-            None => Err(OutOfRangeError { is_signed: false, is_greater_than_max: true }),
-        }
+    #[allow(clippy::missing_panics_doc)]
+    pub fn from_int_btc<T: Into<u32>>(whole_bitcoin: T) -> Amount {
+        Amount::from_int_btc_const(whole_bitcoin.into())
     }
 
     /// Converts from a value expressing a whole number of bitcoin to an [`Amount`]
     /// in const context.
-    ///
-    /// # Panics
-    ///
-    /// The function panics if the argument multiplied by the number of sats
-    /// per bitcoin overflows a `u64` type.
+    #[allow(clippy::missing_panics_doc)]
     pub const fn from_int_btc_const(whole_bitcoin: u32) -> Amount {
-        let btc = whole_bitcoin as u64; // Can't call u64::from in const context.
+        let btc = whole_bitcoin as u64; // Can't call `into` in const context.
         match btc.checked_mul(100_000_000) {
             Some(amount) => Amount::from_sat(amount),
-            None => panic!("checked_mul overflowed"),
+            None => panic!("cannot overflow a u64"),
         }
     }
 
