Source folder name impact on cache

[eandersson]

It looks like the source folder name impacts the caching. Is this intended? If so is there some way to override this? Imagine that you want to clone the same repositories multiple times on the same system and name the checkout after the branch or release without causing the cache to get invalidated.

[MMI]

Not sure about intended but it's how it works. I game this by doing builds in a container and mapping the source to the same directory inside the container -- thus everything looks the same to sccache. You might be able to same thing with a symlink (and if that doesn't work a bind mount).

[MMI]

Also, it's documented here

[KristoferHansson]

Following up on this thread, we started using sccache for our C++/CMake/Ninja projects in 2021 and checked the cloned folder / build path and came to the conclusion that build folder had no effect, caching worked fine regardless. Now in 2024 we saw that we were getting much less cache hits if cloning to another folder than before, noticed that CMake in 3.21 changed a bit on how they handled path generation for Ninja: https://gitlab.kitware.com/cmake/cmake/-/issues/24345

Our hypothesis was that the expansion of __FILE__ used in our assert macros now started expanding to full paths instead of relative, causing cache mismatch if cloned to different paths. We are currently verifying this now and it looks like our hypothesis is correct, we will now also check if we can mitigate the issue by utilizing __builtin_FILE() instead of __FILE__

Update: Looks good and works as we hoped with __builtin_FILE() so now cloned path does not affect cache hits any more again.