Setting CPM_SOURCE_ROOT from the environment about cpm.cmake HOT 10 CLOSED

Yeah I was thinking about something like that, though there could be issues with the Path's name and length if simply appended. Perhaps .cache/CPM/{lowercase name}/{SHA1 Hash of all origin parameters} would work.

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Awesome, thanks!
I've also been testing this for the last days and it works quite well. Some small issues occurred when updating dependencies or clearing the cache, but those should be resolved by now.
I agree, we should rename the var to CPM_SOURCE_CACHE.

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It should be possible to read in an environmental environment and set the value, if it exists. However I believe sharing downloads could easily break if different projects use different versions/sources of the same dependency.
We should investigate this first before endorsing a global download location. Perhaps it's possible to safely encode the version/source information in the download path?
Also note that only the download itself and not the build can be cached, as builds would break when different options or generators are used. For faster builds I recommend checking out caching compiler wrappers such as sccache.

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I use ccache already. It is more about caching the downloads, the version should be in then path name then. If everything is found in the cache then no online connection would be required. I wonder if this is out of scope for CPM. So the cache contains all downloads like this named by CPM params already required?

.cache/CPM/{NAME}-{URL}-{VERSION}

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I've implemented the above suggestion here: CPM.cmake. CPM should now check for the environmental variable CPM_SOURCE_ROOT which should be set to the absolute path of the download directory.
@aggsol It would be great if you could check if that works for your projects and solves your use-case.

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So I just did a simple test and it seems that CMake actually removes the source directories before trying to repopulate them. That kinda makes the whole concept of caching downloads obsolete. I'll investigate if we can change this behaviour.

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I've updated the source to override the download step if the directory already exists: CPM.cmake. Could you check if it works for you now @aggsol ?

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@TheLartians I will give it a go, please gimme some days. Currently busy T_T

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Thanks! NP, I just want to make sure it’s battle tested before publishing as this seems to be a big feature.

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I tested it in two different systems with environment variable and as command line parameter. Different builds and different versions of libraries. I used $HOME/.cache/CPM for both and checked creation of folders and files. This works really good! Maybe the var should be renamed CPM_SOURCE_CACHE then? I will check how it behaves in the following weeks.

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