[carreau]

As I replied to the sibling comment, yes, I agree, but caching is not magic. You need to know what to invalidate, and you need to be allowed to spend time making test group that run depending on what have changed. So without policy and having devs being allowed to work on optimizing CI/reducing time, you can list plenty of strategies to make it faster but it will likely not happen.

[ohgodplsno]

Caching is pretty damn simple with any sensible build tool that simply stores hashes of files and modules. Caching in the JVM ecosystem is pretty much free, for example.

[carreau]

Sure, but you seem to be read this blog post in the narrow view of building as only "compiling an artifact" and not running the test suite across many platforms/condition, or any other work. I mean the author even points out that building the kernel is only a use-case that takes time for measurement purposes. For some projects I work on the compilation itself takes maybe 1/10 max of the total build and test. So even with infinite agressive compilation caching I would not gain much.

[ohgodplsno]

Nope, our Android app has caching, both for building APKs/AABs, but also for test suites. PRs run the entire test suite (on too many variants, even, I forgot to remove some unneeded stuff), what hasn't changed or hasn't been impacted by said changes simply gets a FROM-CACHE and isn't reran.

[ninkendo]

That's great for your android app, and you're lucky you have such a thing. But your experience is not generally applicable to all of software development. There are many, many, many build systems out there in the wild that do not support the ability to know what unit tests are affected by what code changes. I'd wager something like 99% of them.

[substation13]

You can cache tests too if you properly capture the inputs