Misc refactors and cleanups in advance of zero-fee commitments

[TheBlueMatt]

A few renames, some doc cleanups, and the feature bit itself.

[ldk-reviews-bot]

👋 Thanks for assigning @wpaulino as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

[codecov]

Codecov Report

Attention: Patch coverage is 82.24299% with 19 lines in your changes missing coverage. Please review.

Project coverage is 89.23%. Comparing base (4c43a5b) to head (c15b29d).

Files with missing lines	Patch %	Lines
lightning/src/ln/channel.rs	56.52%	10 Missing ⚠️
lightning/src/events/bump_transaction.rs	78.94%	3 Missing and 1 partial ⚠️
lightning/src/ln/chan_utils.rs	82.35%	3 Missing ⚠️
lightning/src/sign/mod.rs	94.11%	0 Missing and 1 partial ⚠️
lightning/src/util/test_channel_signer.rs	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3656      +/-   ##
==========================================
- Coverage   89.24%   89.23%   -0.01%     
==========================================
  Files         155      155              
  Lines      119280   119281       +1     
  Branches   119280   119281       +1     
==========================================
  Hits       106446   106446              
- Misses      10240    10241       +1     
  Partials     2594     2594              

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[tnull]

CI is unhappy:

error[E0034]: multiple applicable items in scope
   --> lightning/src/util/test_channel_signer.rs:463:14
    |
463 |         self.inner.sign_holder_keyed_anchor_input(chan_params, anchor_tx, input, secp_ctx)
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ multiple `sign_holder_keyed_anchor_input` found
    |
note: candidate #1 is defined in an impl of the trait `TaprootChannelSigner` for the type `DynSigner`
   --> lightning/src/util/dyn_signer.rs:121:2
    |
121 | /     fn sign_holder_keyed_anchor_input(
122 | |         &self, anchor_tx: &Transaction, input: usize, secp_ctx: &Secp256k1<All>,
123 | |     ) -> Result<secp256k1::schnorr::Signature, ()> {
    | |__________________________________________________^
note: candidate #2 is defined in an impl of the trait `sign::ecdsa::EcdsaChannelSigner` for the type `DynSigner`
   --> lightning/src/util/mod.rs:101:17
    |
101 |                   fn $f(&$($mu)? self, $($n: $t),*) ->  $r {
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
   ::: lightning/src/util/dyn_signer.rs:134:1
    |
134 | / delegate!(DynSigner, EcdsaChannelSigner, inner,
135 | |     fn sign_holder_commitment(, channel_parameters: &ChannelTransactionParameters,
136 | |         commitment_tx: &HolderCommitmentTransaction,
137 | |         secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()>,
...   |
168 | |         secp_ctx: &Secp256k1<All>) -> Result<Signature, ()>
169 | | );
    | |_- in this macro invocation
    = note: this error originates in the macro `delegate` (in Nightly builds, run with -Z macro-backtrace for more info)
help: disambiguate the method for candidate #1
    |
463 |         TaprootChannelSigner::sign_holder_keyed_anchor_input(&self.inner, chan_params, anchor_tx, input, secp_ctx)
    |
help: disambiguate the method for candidate #2
    |
463 |         sign::ecdsa::EcdsaChannelSigner::sign_holder_keyed_anchor_input(&self.inner, chan_params, anchor_tx, input, secp_ctx)
    |

[TheBlueMatt]

Just removed the method on the taproot signer.

[valentinewallace]

full_stack fuzz is failing

[valentinewallace]

LGTM after fuzz is fixed

[ldk-reviews-bot]

👋 The first review has been submitted!

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[wpaulino]

LGTM

[wpaulino]

Good to squash, CI is still sad

[TheBlueMatt]

Squashed:

$ git diff-tree -U1 02ce69e59 68b16e24c
diff --git a/lightning/src/events/bump_transaction.rs b/lightning/src/events/bump_transaction.rs
index 77943845c..a9550a672 100644
--- a/lightning/src/events/bump_transaction.rs
+++ b/lightning/src/events/bump_transaction.rs
@@ -98,3 +98,3 @@ impl AnchorDescriptor {
 		} else {
-			debug_assert!(tx_params.channel_type_features.supports_zero_fee_commitments());
+			debug_assert!(tx_params.channel_type_features.supports_anchor_zero_fee_commitments());
 			Witness::from_slice(&[&[]])