[WIP] Shade Feign 8.17

[jeremyk-91]

Goals (and why): Shade Feign, so that several internal products (including shopping and blob store) will not explode from dependency conflicts. In the current state this is largely an outline of how I intend to implement this across Feign-using AtlasDB projects.

• Finish adding feign-shading to all feign-using projects.
• Test that we can still deploy timelock after this change.
• Test that we can use internal shopping product after this change with no hiccups.
• Release notes.

Implementation Description (bullets):

• We introduce a concept of 'lean' jars, which are built without any form of shadowing and used internally (even for things like AtlasDB Config where we currently always shadow). This allows us to easily depend on classes pulled in by our projects without worrying about scenarios like this:

        PingableLeader ping = Feign.builder()
                .decoder(new TextDelegateDecoder(new JacksonDecoder()))
// fails, because a com.palantir.shaded.JacksonDecoder is not a feign.Decoder (even though it is a com.palantir.shaded.Decoder)

• So for each project, we internally depend on lean jars where necessary, but we only publish shadowed jars. The shadowing takes place in feign-shading.gradle plus possibly other dependency rules in projects that already publish shadow jars (atlasdb-cassandra and atlasdb-config, most notably).
• Generally dependencies should use the explicitShadow configuration (be used both at compile time and at runtime in the shadow jar). The Feign dependencies, however, should use the compile configuration (they should not be present at runtime in the shadow jar, because they are being shaded away).
• There are some slightly trickier shenanigans for Dagger and Remoting2, where projects already shade some of their dependencies and we want to keep them shaded. The daggerShadowJar and remotingShadowJar basically shade these components, but not Feign.

Concerns (what feedback would you like?):

• Will we accidentally publish the lean jars? My understanding of publish-jars.gradle suggests that it's able to pick the shadow jar if one exists. Publication was a bit funky because of an API break in Shadow in 2.0.0, but looking at my Maven caches after a publishToMavenLocal we do indeed publish the right jars.
• I'm removing the prohibition on generating the non-shadow/lean jar for atlasdb-config and atlasdb-cassandra (with the understanding that only the shadow jar will ever be published). For config given that this only touches a bunch of (very stable) Remoting2 classes I think we're safe. I'm not so sure about Cassandra.
• Is there a better way to do this?

Where should we start reviewing?: feign-shading.gradle

Priority (whenever / two weeks / yesterday): ASAP; is a release-blocker.

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This change is 

[codecov-io]

Codecov Report

Merging #2054 into develop will increase coverage by 4.85%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             develop    #2054      +/-   ##
=============================================
+ Coverage      57.77%   62.62%   +4.85%     
- Complexity      4066     4068       +2     
=============================================
  Files            754      754              
  Lines          37240    37240              
  Branches        4028     4028              
=============================================
+ Hits           21514    23322    +1808     
+ Misses         14295    12387    -1908     
- Partials        1431     1531     +100

Impacted Files	Coverage Δ	Complexity Δ
.../atlasdb/transaction/impl/AbstractTransaction.java	60% <0%> (-20%)	3% <0%> (ø)
...in/java/com/palantir/paxos/PaxosAcceptorState.java	60.52% <0%> (-18.43%)	0% <0%> (ø)
...r/atlasdb/schema/stream/StreamStoreDefinition.java	55.55% <0%> (-14.82%)	4% <0%> (ø)
...tlasdb/transaction/impl/ForwardingTransaction.java	73.07% <0%> (-11.54%)	14% <0%> (ø)
...ain/java/com/palantir/paxos/PaxosAcceptorImpl.java	62.5% <0%> (-10.72%)	0% <0%> (ø)
...a/com/palantir/atlasdb/ptobject/EncodingUtils.java	74.74% <0%> (-5.06%)	62% <0%> (ø)
...in/java/com/palantir/paxos/PaxosQuorumChecker.java	71.18% <0%> (-3.39%)	0% <0%> (ø)
.../impl/ValidatingQueryRewritingKeyValueService.java	35.04% <0%> (-2.57%)	21% <0%> (ø)
...com/palantir/atlasdb/table/description/Schema.java	76.3% <0%> (-2.32%)	26% <0%> (ø)
.../atlasdb/stream/AbstractPersistentStreamStore.java	76.34% <0%> (-2.16%)	17% <0%> (ø)
... and 48 more

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[jeremyk-91]

Need to add this back as a runtime dep

[jeremyk-91]

(or not, already added in the distribution project)

[gmaretic]

LGTM! As discussed offline, would be good to document how exactly the dagger/remoting shading works with feign shading!

[jeremyk-91]

This won't actually work because clients often pull in multiple AtlasDB jars, so will have multiple copies of the Feign classes. Also there's a lot of hackery with getting the nebula dependency recommender and the shadow plugin to play nicely with each other.

Was hoping not to have to do some surgery on the src/java itself, but looks like we'll have to! The plan going forward is to set up a new atlas-feign project and use that instead.

Closing out. 😞 I guess I've learned a fair bit about shadowing and Gradle though!

[jeremyk-91]

(N.B. Please don't delete the branch until the new fix merges.)