Speed up CI

[mattsse]

Issue summary

• The CI appears to recompile everything on every PR, ideally we should cache at least all the polkadot/substrate related dependencies.

Other information and links

[clearloop]

Already cached with sccache

• PINT/.circleci/config.yml

  Line 90 in 84acda4

  save_build_cache:

• PINT/.circleci/config.yml

  Line 53 in 84acda4

  sccache_setup:

[mattsse]

hmm judging from the CI logs, it appears the environment is always set up new and all dependencies installed, but I don't really have much experience with configuring this for optimization.

[clearloop]

Caching target directory will cause some related issues, for example

• we remove a feature and related code in one PR
• we get back the feature but forget to get back the related code
• the project still can compile

---

• build-cache
• moonbeam also use sccache

[mattsse]

Please add your planning poker estimate with ZenHub @clearloop

[ptqa]

FYI

• There is a tool for optimizing docker layer caching for rust (see https://github.com/LukeMathWalker/cargo-chef)
• But this only works for local development and circleci docker caching is working poorly. So I would suggest using kaniko cache strategy (see https://github.com/GoogleContainerTools/kaniko#caching), this allows storing cache layers in docker registry.