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I've been building Swift using the instructions from swift/GettingStarted.md at main · apple/swift · GitHub. When I tried to execute the following (from the actual build section):

utils/build-script --skip-build-benchmarks \
  --skip-ios --skip-watchos --skip-tvos --swift-darwin-supported-archs "$(uname -m)" \
  --sccache --release-debuginfo --swift-disable-dead-stripping --test

and see how sccache is doing with sccache --show-stats. It seems that sccache isn't caching:

Compile requests                    625
Compile requests executed             0
Cache hits                            0
Cache misses                          0
Cache timeouts                        0
Cache read errors                     0
Forced recaches                       0
Cache write errors                    0
Compilation failures                  0
Cache errors                          0
Non-cacheable compilations            0
Non-cacheable calls                 625
Non-compilation calls                 0
Unsupported compiler calls            0
Average cache write               0.000 s
Average cache read miss           0.000 s
Average cache read hit            0.000 s
Failed distributed compilations       0

Non-cacheable reasons:
multiple -arch                      625

Cache location                  Local disk: "<path to Library>/Caches/Mozilla.sccache"
Cache size                            0 bytes
Max cache size                       10 GiB

It seems that sccache isn't caching the compilation.

Is this expected? Is there a flag(s) that I can use on the build script to ensure sccache? Am I just misinterpreting the output?

I've been using sccache 0.2.15` if that helps.

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I did not go back to check this, but when i tried sccache a while ago, it was not able to read a lot of the compilation lines because it thought that there were multiple output files. Sccache was misunderstanding one of the compilation flags as adding another output file if i remember it correctly. It was a problem in sccache at least as i understood it. I might be misremembering, like i said i did not recheck this before writing this.

Can you check the logs of the sccache server process and see if it’s rejecting because it thinks there are multiple output files?

3

This is a recent issue with newer versions of sccache, you can see [docs] Add warning that sccache isn't caching any commands since version 0.13.4 by ahoppen · Pull Request #35777 · apple/swift · GitHub for some details but the solution is to install 2.13 or earlier for now.

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