Log penalty info in route-success line

[jurvis]

This PR is an attempt at #1233.

My goal is to be able to leverage on the existing log_route! macro to print the penalties for each path found within a route, which meant making the penalty data available somehow in the Route struct.

I think this contribution can be improved by adding test coverage, but am struggling to figure out where to add them. Suggestions welcome!

I'm new to Rust + contributing to open-source, so please feel free to leave feedback! I am also happy to change the implementation if adding a field to Route is not something we want to pursue.

Thanks!

Demo

This is the old output for routes (ran via routing::router::tests::simple_route_test):

INFO   [lightning::routing::router : lightning/src/routing/router.rs, 1538] Got route to 03462779ad4aad39514614751a71085f2f10e1c7a593e4e030efb5b8721ce55b0b: path 0:
 node_id: 02531fe6068134503d2723133227c867ac8fa6c83c537e9a44c3c5bdbdcb1fe337, short_channel_id: 2, fee_msat: 100, cltv_expiry_delta: 65
 node_id: 03462779ad4aad39514614751a71085f2f10e1c7a593e4e030efb5b8721ce55b0b, short_channel_id: 4, fee_msat: 100, cltv_expiry_delta: 42

New (diff in ****):

INFO   [lightning::routing::router : lightning/src/routing/router.rs, 1538] Got route to 03462779ad4aad39514614751a71085f2f10e1c7a593e4e030efb5b8721ce55b0b: path 0 **(penalty: 0)**:
 node_id: 02531fe6068134503d2723133227c867ac8fa6c83c537e9a44c3c5bdbdcb1fe337, short_channel_id: 2, fee_msat: 100, cltv_expiry_delta: 65
 node_id: 03462779ad4aad39514614751a71085f2f10e1c7a593e4e030efb5b8721ce55b0b, short_channel_id: 4, fee_msat: 100, cltv_expiry_delta: 42

[codecov-commenter]

Codecov Report

Merging #1300 (0acc230) into main (d29ae18) will decrease coverage by 0.02%.
The diff coverage is 85.00%.

@@            Coverage Diff             @@
##             main    #1300      +/-   ##
==========================================
- Coverage   90.51%   90.48%   -0.03%     
==========================================
  Files          71       71              
  Lines       39012    39025      +13     
==========================================
+ Hits        35310    35313       +3     
- Misses       3702     3712      +10     

Impacted Files	Coverage Δ
lightning/src/routing/router.rs	91.69% <75.00%> (-0.11%)	⬇️
lightning-invoice/src/payment.rs	92.69% <100.00%> (-0.07%)	⬇️
lightning/src/ln/functional_tests.rs	97.20% <100.00%> (-0.08%)	⬇️
lightning/src/ln/onion_utils.rs	95.65% <100.00%> (+0.01%)	⬆️
lightning/src/util/macro_logger.rs	85.48% <100.00%> (ø)
lightning-invoice/src/de.rs	81.06% <0.00%> (-0.21%)	⬇️

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[TheBlueMatt]

I can't leave a comment there (thanks GitHub...) but maybe instead of changing the public API a bunch we could try to clean up the output printed at L1319 (presumably by doing a custom debug representation of PathBuildingHop instead of the default one).

[TheBlueMatt]

Hmm, do we care about actually exposing this programmatically? Presumably the user can just call their own scorer immediately after getting the route if they really want this info. I think just logging it may be sufficient.

[jurvis]

hi @TheBlueMatt, thanks for taking a look! that is a good suggestion -- I'll change my implementation. I will take another stab over the weekend :)

[jurvis]

attempting different implementation, closing.