Expand CPM_SOURCE_CACHE path provided as a configure argument

[iboB]

Long story:

If one relies on get_cpm.cmake instead of a manual copy of CPM.cmake, and configures with -DCPM_SOURCE_CACHE=~/some/path (with a tilde which they expect to be expanded to $HOME), this CMake issue hits and thus the EXISTS check always fails, and file(DOWNLOAD always fails (one would expect that it would create the directory \~ (literal tilde) but it doesn't... anyway)

Further when CPM.cmake gets included CPM_SOURCE_CACHE is cached as CACHE PATH which does the expansion and subsequent code is not affected by the tilde. That's why nothing special needs to be done for the actual CPM.cmake code. It works even if used by a manual copy and not through get_cpm.

[TheLartians]

Interesting. Probably we should also expand ENV{CPM_SOURCE_CACHE} as I suppose environmental variables like export CPM_SOURCE_CACHE=~/some/path cmake are effected similarly?

[iboB]

It's pretty hard to add a tilde in an env var. Your export example will expand it and the environment variable will contain what's expected

[iboB]

One would need to make special effort to confuse the environment variable check... and I suppose if they do, then for some reason they do want the literal tilde

[TheLartians]

It's pretty hard to add a tilde in an env var. Your export example will expand it and the environment variable will contain what's expected

Huh, you're right, who would have thought that shell expansion can be that confusing 😅

[TheLartians]

FYI: the feature is live in 0.28.1 🎉