Use Simulacrum Scalafix

[travisbrown]

Addresses #3192, using a new release of Simulacrum Scalafix. An earlier version of this change was included in #3269, but I think it should be reviewed and merged separately from the Dotty cross-build work (we'll need to decide which Dotty version to support, since for example there's still no official 0.23 or 0.24 release of the scalatestplus dependency, but I don't think that should block this change).

The Scalafix commit was generated by running the following commands:

sbt:cats> scalafix AddSerializable
sbt:cats> scalafix AddImplicitNotFound
sbt:cats> scalafix TypeClassSupport
sbt:cats> scalafmtAll

These commands will need to be run manually after any API change that needs syntax support. I haven't added this process to the validateJVM task yet, but they're idempotent and only take a few seconds, so I guess we could run them on every build.

[codecov-commenter]

Codecov Report

Merging #3424 into master will decrease coverage by 1.11%.
The diff coverage is 50.18%.

@@            Coverage Diff             @@
##           master    #3424      +/-   ##
==========================================
- Coverage   92.65%   91.54%   -1.12%     
==========================================
  Files         379      379              
  Lines        7994     8209     +215     
  Branches      227      227              
==========================================
+ Hits         7407     7515     +108     
- Misses        587      694     +107     

Flag	Coverage Δ
#scala_version_212	91.53% <50.18%> (-1.15%)	⬇️
#scala_version_213	91.33% <50.18%> (-1.09%)	⬇️

Impacted Files	Coverage Δ
...lleycats-core/src/main/scala/alleycats/ConsK.scala	0.00% <0.00%> (ø)
...lleycats-core/src/main/scala/alleycats/Empty.scala	0.00% <0.00%> (ø)
...leycats-core/src/main/scala/alleycats/EmptyK.scala	0.00% <0.00%> (ø)
...eycats-core/src/main/scala/alleycats/Extract.scala	0.00% <0.00%> (ø)
alleycats-core/src/main/scala/alleycats/One.scala	0.00% <0.00%> (ø)
alleycats-core/src/main/scala/alleycats/Pure.scala	0.00% <0.00%> (ø)
alleycats-core/src/main/scala/alleycats/Zero.scala	0.00% <0.00%> (ø)
core/src/main/scala/cats/Alternative.scala	70.58% <0.00%> (-21.72%)	⬇️
core/src/main/scala/cats/Applicative.scala	90.47% <0.00%> (-4.53%)	⬇️
core/src/main/scala/cats/Bifoldable.scala	68.42% <0.00%> (-24.44%)	⬇️
... and 40 more

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[rossabaker]

I'm usually against checked in generated source, but I feel better after rereading the linked ticket. I think this is our best option at present. 👍

[kailuowang]

I like this approach.

haven't added this process to the validateJVM task yet,

Just curious, so the plan is to have validateJVM generate code and add commits to PRs from CI?

[travisbrown]

@kailuowang I think API changes that map over to codegen changes will be infrequent enough that we can run it manually for now. If it turns out that that's not the case and we're getting a lot of PRs with missing codegen changes, we could tie these tasks into validateJVM or prePR, so that they'd be run when people build locally.

I guess we could also have something more automated in CI, but that seems unnecessary for something that's likely to happen once every month or two.

[travisbrown]

Thanks all! I'm merging this with a merge commit to keep the automated changes separate from the configuration that sets them up. I'll update the Dotty cross-building branch later today or tomorrow.