Merge rust-bitcoin/rust-bitcoin#3726: units: Improve `Default`

a4a0f2921c units: Add regression tests for Default impls (Tobin C. Harding)
f5c2248a31 units: Derive Default for BlockInterval (Tobin C. Harding)

Pull request description:

  Done while looking into [C-TOR](https://rust-lang.github.io/api-guidelines/predictability.html#c-ctor)

  - Derive `Default` for `BlockInterval`
  - Add regression test for all types that implement `Default`

ACKs for top commit:
  apoelstra:
    ACK a4a0f2921cd2425fa46a8ade42f888d5268e6709; successfully ran local tests

Tree-SHA512: ce39c2bcb37fc0fa70bd2553dd7843d9ac8f9528631706056ba89fda9623defadf32974091832b7a087121290b3f883bc8a8dcca070f1d90670eeee6b541de01

units/src/block.rs

@@ -93,7 +93,7 @@ impl TryFrom<BlockHeight> for absolute::Height {
 ///
 /// This type is not meant for constructing relative height based timelocks, this is a general
 /// purpose block interval abstraction. For locktimes please see [`locktime::relative::Height`].
-#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 // Public to try and make it really clear that there are no invariants.
 pub struct BlockInterval(pub u32);

units/tests/api.rs

@@ -98,12 +98,13 @@ struct CommonTraits {
 }
 
 /// A struct that includes all types that implement `Default`.
-#[derive(Default)] // C-COMMON-TRAITS: `Default`
+#[derive(Debug, Default, PartialEq, Eq)] // C-COMMON-TRAITS: `Default`
 struct Default {
     a: Amount,
     b: SignedAmount,
-    c: relative::Height,
-    d: relative::Time,
+    c: BlockInterval,
+    d: relative::Height,
+    e: relative::Time,
 }
 
 /// A struct that includes all public error types.
@@ -249,3 +250,16 @@ fn test_sync() {
     assert_sync::<Types>();
     assert_sync::<Errors>();
 }
+
+#[test]
+fn regression_default() {
+    let got: Default = Default::default();
+    let want = Default {
+        a: Amount::ZERO,
+        b: SignedAmount::ZERO,
+        c: BlockInterval::ZERO,
+        d: relative::Height::ZERO,
+        e: relative::Time::ZERO,
+    };
+    assert_eq!(got, want);
+}