Add concrete NO_* consts to avoid users having to specify types

[TheBlueMatt]

When building a background processor without an onion messenger or liquidity manager, users still need to pass None into the background processor initialization methods. Sadly, Rust will require a concrete type for the (unused) Some variant of the Option passed in, which requires specifying out a lot of type gook.

Instead, provide some constants which users can pass in trivially.

Fixes#3612

[ldk-reviews-bot]

👋 Thanks for assigning @tnull 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

❌ Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.69%. Comparing base (1ed6c4b) to head (0d59d73).
⚠️ Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning-background-processor/src/lib.rs	90.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #4100 +/- ##
==========================================
- Coverage 88.71% 88.69% -0.02% 
==========================================
Files 176 176 Lines 132778 132859 +81 Branches 132778 132859 +81 ==========================================
+ Hits 117790 117836 +46 - Misses 12304 12336 +32 - Partials 2684 2687 +3 

Flag	Coverage Δ
fuzzing	21.55% <ø> (+<0.01%)	⬆️
tests	88.53% <90.00%> (-0.02%)	⬇️

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[tnull]

ACK. I still think a builder pattern would be the prettier solution here (if we could make it work), but given how few users will actually use the raw background processor going forward, spending much more time on optimizing the API (esp. after we already spent some time over at #3688) probably doesn't make sense for now.

Note that CI is failing, also

[TheBlueMatt]

$ git diff-tree -U1 9ee959c533 e76eb2ed5e
diff --git a/lightning-background-processor/src/lib.rs b/lightning-background-processor/src/lib.rs
index 1ce0f1dd12..b7e67f1667 100644
--- a/lightning-background-processor/src/lib.rs+++ b/lightning-background-processor/src/lib.rs@@ -3476,6 +3476,24 @@ mod tests {
#[test]
-	fn test_no_moves() {- // Make sure the NO_* constants can be moved so that they can be passed to BP methods.- let no_liq = crate::NO_LIQUIDITY_MANAGER;- let no_om = crate::NO_ONION_MESSENGER;+	fn test_no_consts() {+ // Compile-test the NO_* constants can be used.+ let (_, nodes) = create_nodes(1, "test_no_consts");+ let data_dir = nodes[0].kv_store.get_data_dir();+ let persister = Arc::new(Persister::new(data_dir));+ let bg_processor = BackgroundProcessor::start(+ persister,+ move |_: Event| Ok(()),+ Arc::clone(&nodes[0].chain_monitor),+ Arc::clone(&nodes[0].node),+ crate::NO_ONION_MESSENGER,+ nodes[0].no_gossip_sync(),+ Arc::clone(&nodes[0].peer_manager),+ crate::NO_LIQUIDITY_MANAGER,+ Some(Arc::clone(&nodes[0].sweeper)),+ Arc::clone(&nodes[0].logger),+ Some(Arc::clone(&nodes[0].scorer)),+ );++ if !std::thread::panicking() {+ bg_processor.stop().unwrap();+ }
}

[TheBlueMatt]

Oops, fixed the CI issues

$ git diff-tree -U1 e76eb2ed5e eafb72d649
diff --git a/lightning-background-processor/src/lib.rs b/lightning-background-processor/src/lib.rs
index b7e67f1667..350908adb7 100644
--- a/lightning-background-processor/src/lib.rs+++ b/lightning-background-processor/src/lib.rs@@ -86,2 +86,4 @@ use std::time::Instant;
use alloc::boxed::Box;
+#[cfg(not(feature = "std"))]+use alloc::sync::Arc;@@ -3476,2 +3478,3 @@ mod tests {
#[test]
+	#[cfg(not(c_bindings))]
fn test_no_consts() {

[valentinewallace]

I believe there's still CI issues?

[TheBlueMatt]

Yep, stuff that wasn't being checked in a local ci/ci-tests.sh run :/

$ git diff-tree -U1 eafb72d64 cd7e3479f
diff --git a/lightning-background-processor/src/lib.rs b/lightning-background-processor/src/lib.rs
index 350908adb7..dcf433605e 100644
--- a/lightning-background-processor/src/lib.rs+++ b/lightning-background-processor/src/lib.rs@@ -86,3 +86,3 @@ use std::time::Instant;
use alloc::boxed::Box;
-#[cfg(not(feature = "std"))]+#[cfg(all(not(c_bindings), not(feature = "std")))]
use alloc::sync::Arc;
@@ -360,2 +360,13 @@ type DynMessageRouter = lightning::onion_message::messenger::DefaultMessageRoute
+#[cfg(all(not(c_bindings), not(taproot)))]+type DynSignerProvider = dyn lightning::sign::SignerProvider<+	EcdsaSigner = lightning::sign::InMemorySigner,+>;++#[cfg(all(not(c_bindings), taproot))]+type DynSignerProvider = dyn lightning::sign::SignerProvider<+	EcdsaSigner = lightning::sign::InMemorySigner,+	TaprootSigner = lightning::sign::InMemorySigner,+>;+
#[cfg(not(c_bindings))]
@@ -366,3 +377,3 @@ type DynChannelManager = lightning::ln::channelmanager::ChannelManager<
&'static dyn lightning::sign::NodeSigner,
-	&'static dyn lightning::sign::SignerProvider<EcdsaSigner = lightning::sign::InMemorySigner>,+	&'static DynSignerProvider,
&'static dyn FeeEstimator,