Move CheckedSum trait to crate root

In order to add other types to CheckedSum, remove from the Amount
module.  In so doing, other types added to CheeckSum do not need to be
imported into Amount.

bitcoin/src/lib.rs

@@ -204,14 +204,15 @@ pub mod amount {
 
     #[rustfmt::skip]            // Keep public re-exports separate.
     #[doc(inline)]
+    pub use units::CheckedSum;
+    #[cfg(feature = "serde")]
+    pub use units::amount::serde;
     pub use units::amount::{
-        Amount, CheckedSum, Denomination, Display, InvalidCharacterError, MissingDenominationError,
+        Amount, Denomination, Display, InvalidCharacterError, MissingDenominationError,
         MissingDigitsError, OutOfRangeError, ParseAmountError, ParseDenominationError, ParseError,
         PossiblyConfusingDenominationError, SignedAmount, TooPreciseError,
         UnknownDenominationError,
     };
-    #[cfg(feature = "serde")]
-    pub use units::amount::serde;
 
     impl Decodable for Amount {
         #[inline]

units/src/amount/mod.rs

@@ -26,6 +26,7 @@ use core::str::FromStr;
 use arbitrary::{Arbitrary, Unstructured};
 
 use self::error::{MissingDigitsKind, ParseAmountErrorInner, ParseErrorInner};
+use crate::CheckedSum;
 
 #[rustfmt::skip]                // Keep public re-exports separate.
 #[doc(inline)]
@@ -593,13 +594,6 @@ enum DisplayStyle {
     DynamicDenomination,
 }
 
-/// Calculates the sum over the iterator using checked arithmetic.
-pub trait CheckedSum<R>: sealed::Sealed<R> {
-    /// Calculates the sum over the iterator using checked arithmetic. If an
-    /// overflow happens it returns [`None`].
-    fn checked_sum(self) -> Option<R>;
-}
-
 impl<T> CheckedSum<Amount> for T
 where
     T: Iterator<Item = Amount>,
@@ -616,16 +610,6 @@ where
     }
 }
 
-mod sealed {
-    use super::{Amount, SignedAmount};
-
-    /// Used to seal the `CheckedSum` trait
-    pub trait Sealed<A> {}
-
-    impl<T> Sealed<Amount> for T where T: Iterator<Item = Amount> {}
-    impl<T> Sealed<SignedAmount> for T where T: Iterator<Item = SignedAmount> {}
-}
-
 #[cfg(feature = "arbitrary")]
 impl<'a> Arbitrary<'a> for Denomination {
     fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {

units/src/lib.rs

@@ -69,3 +69,20 @@ pub(crate) use self::result::OptionExt;
 #[deprecated(since = "TBD", note = "use `BlockHeightInterval` instead")]
 #[doc(hidden)]
 pub type BlockInterval = BlockHeightInterval;
+
+/// Calculates the sum over the iterator using checked arithmetic.
+pub trait CheckedSum<R>: sealed::Sealed<R> {
+    /// Calculates the sum over the iterator using checked arithmetic. If an
+    /// overflow happens it returns [`None`].
+    fn checked_sum(self) -> Option<R>;
+}
+
+mod sealed {
+    use super::{Amount, SignedAmount};
+
+    /// Used to seal the `CheckedSum` trait
+    pub trait Sealed<A> {}
+
+    impl<T> Sealed<Amount> for T where T: Iterator<Item = Amount> {}
+    impl<T> Sealed<SignedAmount> for T where T: Iterator<Item = SignedAmount> {}
+}

units/tests/api.rs

@@ -15,7 +15,7 @@ use arbitrary::{Arbitrary, Unstructured};
 use bitcoin_units::locktime::{absolute, relative}; // Typical usage is `absolute::Height`.
 use bitcoin_units::{
     amount, block, fee_rate, locktime, parse, weight, Amount, BlockHeight, BlockInterval, BlockMtp,
-    BlockMtpInterval, BlockTime, FeeRate, SignedAmount, Weight,
+    BlockMtpInterval, BlockTime, CheckedSum, FeeRate, SignedAmount, Weight,
 };
 
 /// A struct that includes all public non-error enums.
@@ -272,7 +272,7 @@ fn regression_default() {
 fn dyn_compatible() {
     // If this builds then traits are dyn compatible.
     struct Traits {
-        a: Box<dyn amount::CheckedSum<Amount>>,
+        a: Box<dyn CheckedSum<Amount>>,
         // These traits are explicitly not dyn compatible.
         // b: Box<dyn amount::serde::SerdeAmount>,
         // c: Box<dyn amount::serde::SerdeAmountForOpt>,