Only include `derive_add_tweak` for base key types that use it

Specifically `RevocationBasepoint` has a different derivation, so
shouldn't have a `derive_add_tweak` at all. We also use this
opportunity to link to the `from_basepoint` function in the
`derive_add_tweak` docs.

diff --git a/lightning/src/ln/channel_keys.rs b/lightning/src/ln/channel_keys.rs
index eaa14f27f3312aa613e449c7d8084183a3cdee4b..9e839b15e3c40636c72553b32c9eb52f35079f7b 100644 (file)
--- a/lightning/src/ln/channel_keys.rs
+++ b/lightning/src/ln/channel_keys.rs
@@ -31,26 +31,30 @@ macro_rules! doc_comment {
        };
 }
 macro_rules! basepoint_impl {
-       ($BasepointT:ty) => {
+       ($BasepointT:ty $(, $KeyName: expr)?) => {
                impl $BasepointT {
                        /// Get inner Public Key
                        pub fn to_public_key(&self) -> PublicKey {
                                self.0
                        }
 
-                       /// Derives the "tweak" used to calculate the per-commitment private key.
-                       ///
-                       /// The per-commitment private key is calculates a private key as:
-                       /// `privkey = basepoint_secret + SHA256(per_commitment_point || basepoint)`
-                       ///
-                       /// This calculates the hash part in the tweak derivation process, which is used to
-                       /// ensure that each key is unique and cannot be guessed by an external party.
-                       pub fn derive_add_tweak(&self, per_commitment_point: &PublicKey) -> Sha256 {
-                               let mut sha = Sha256::engine();
-                               sha.input(&per_commitment_point.serialize());
-                               sha.input(&self.to_public_key().serialize());
-                               Sha256::from_engine(sha)
-                       }
+                       $(doc_comment!(
+                               concat!(
+                               "Derives the \"tweak\" used in calculate [`", $KeyName, "::from_basepoint`].\n",
+                               "\n",
+                               "[`", $KeyName, "::from_basepoint`] calculates a private key as:\n",
+                               "`privkey = basepoint_secret + SHA256(per_commitment_point || basepoint)`\n",
+                               "\n",
+                               "This calculates the hash part in the tweak derivation process, which is used to\n",
+                               "ensure that each key is unique and cannot be guessed by an external party."
+                               ),
+                               pub fn derive_add_tweak(&self, per_commitment_point: &PublicKey) -> Sha256 {
+                                       let mut sha = Sha256::engine();
+                                       sha.input(&per_commitment_point.serialize());
+                                       sha.input(&self.to_public_key().serialize());
+                                       Sha256::from_engine(sha)
+                               });
+                       )?
                }
 
                impl From<PublicKey> for $BasepointT {
@@ -110,7 +114,7 @@ macro_rules! key_read_write {
 /// state broadcasted was previously revoked.
 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
 pub struct DelayedPaymentBasepoint(pub PublicKey);
-basepoint_impl!(DelayedPaymentBasepoint);
+basepoint_impl!(DelayedPaymentBasepoint, "DelayedPaymentKey");
 key_read_write!(DelayedPaymentBasepoint);
 
 /// A derived key built from a [`DelayedPaymentBasepoint`] and `per_commitment_point`.
@@ -137,7 +141,7 @@ key_read_write!(DelayedPaymentKey);
 /// Thus, both channel counterparties' HTLC keys will appears in each HTLC output's script.
 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
 pub struct HtlcBasepoint(pub PublicKey);
-basepoint_impl!(HtlcBasepoint);
+basepoint_impl!(HtlcBasepoint, "HtlcKey");
 key_read_write!(HtlcBasepoint);
 
 /// A derived key built from a [`HtlcBasepoint`] and `per_commitment_point`.