Universally Require Writeable for ChannelKeys

It doesn't make sense to ever build a lightning node which doesn't
ever write ChannelMonitors to disk, so having a ChannelKeys object
which doesn't implement Writeable is nonsense.

Here we require Writeable for all ChannelKeys objects, simplifying
code generation for C bindings somewhat.

Author: TheBlueMatt

lightning-persister/src/lib.rs

@@ -43,7 +43,7 @@ trait DiskWriteable {
 	fn write(&self, writer: &mut fs::File) -> Result<(), Error>;
 }
 
-impl<ChanSigner: ChannelKeys + Writeable> DiskWriteable for ChannelMonitor<ChanSigner> {
+impl<ChanSigner: ChannelKeys> DiskWriteable for ChannelMonitor<ChanSigner> {
 	fn write(&self, writer: &mut fs::File) -> Result<(), Error> {
 		self.serialize_for_disk(writer)
 	}
@@ -94,7 +94,7 @@ impl FilesystemPersister {
 	}
 
 	#[cfg(test)]
-	fn load_channel_data<ChanSigner: ChannelKeys + Readable + Writeable>(&self) ->
+	fn load_channel_data<ChanSigner: ChannelKeys + Readable>(&self) ->
 		Result<HashMap<OutPoint, ChannelMonitor<ChanSigner>>, ChannelMonitorUpdateErr> {
 		if let Err(_) = fs::create_dir_all(&self.path_to_channel_data) {
 			return Err(ChannelMonitorUpdateErr::PermanentFailure);
@@ -128,7 +128,7 @@ impl FilesystemPersister {
 	}
 }
 
-impl<ChanSigner: ChannelKeys + Readable + Writeable + Send + Sync> channelmonitor::Persist<ChanSigner> for FilesystemPersister {
+impl<ChanSigner: ChannelKeys + Readable + Send + Sync> channelmonitor::Persist<ChanSigner> for FilesystemPersister {
 	fn persist_new_channel(&self, funding_txo: OutPoint, monitor: &ChannelMonitor<ChanSigner>) -> Result<(), ChannelMonitorUpdateErr> {
 		self.write_channel_data(funding_txo, monitor)
 		  .map_err(|_| ChannelMonitorUpdateErr::PermanentFailure)

lightning/src/chain/channelmonitor.rs

@@ -755,7 +755,7 @@ impl<ChanSigner: ChannelKeys> PartialEq for ChannelMonitor<ChanSigner> {
 	}
 }
 
-impl<ChanSigner: ChannelKeys + Writeable> ChannelMonitor<ChanSigner> {
+impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 	/// Writes this monitor into the given writer, suitable for writing to disk.
 	///
 	/// Note that the deserializer is only implemented for (Sha256dHash, ChannelMonitor), which

lightning/src/chain/keysinterface.rs

@@ -204,7 +204,7 @@ impl Readable for SpendableOutputDescriptor {
 // routine).
 // TODO: We should remove Clone by instead requesting a new ChannelKeys copy when we create
 // ChannelMonitors instead of expecting to clone the one out of the Channel into the monitors.
-pub trait ChannelKeys : Send+Clone {
+pub trait ChannelKeys : Send+Clone + Writeable {
 	/// Gets the per-commitment point for a specific commitment number
 	///
 	/// Note that the commitment number starts at (1 << 48) - 1 and counts backwards.

lightning/src/ln/channel.rs

@@ -4074,7 +4074,7 @@ impl Readable for InboundHTLCRemovalReason {
 	}
 }
 
-impl<ChanSigner: ChannelKeys + Writeable> Writeable for Channel<ChanSigner> {
+impl<ChanSigner: ChannelKeys> Writeable for Channel<ChanSigner> {
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ::std::io::Error> {
 		// Note that we write out as if remove_uncommitted_htlcs_and_mark_paused had just been
 		// called but include holding cell updates (and obviously we don't modify self).

lightning/src/ln/onchaintx.rs

@@ -287,7 +287,7 @@ pub struct OnchainTxHandler<ChanSigner: ChannelKeys> {
 	secp_ctx: Secp256k1<secp256k1::All>,
 }
 
-impl<ChanSigner: ChannelKeys + Writeable> OnchainTxHandler<ChanSigner> {
+impl<ChanSigner: ChannelKeys> OnchainTxHandler<ChanSigner> {
 	pub(crate) fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ::std::io::Error> {
 		self.destination_script.write(writer)?;
 		self.holder_commitment.write(writer)?;