GTest dependency checking hardcodes `/usr`

[rossburton]

When searching for googletest meson will forcibly look in hard-coded /usr paths:

meson/mesonbuild/dependencies/dev.py

Line 57 in e4bbc63

self.src_dirs = ['/usr/src/gtest/src', '/usr/src/googletest/googletest/src']

This causes problems when you're doing builds in sysroots and such like.

A previous MR to attempt to resolve this was filed (#5919) but closed as there wasn't a clear idea on how to proceed without hardcoding /usr/.

Then again, googletest has had a pkgconfig file since 2017 in release 1.8.1 onwards (google/googletest@8604c4a), so is the non-pkgconfig codepath still actually useful?

[dcbaker]

This only gets called if gtest is available as source installed by a distro, and not as a built library. At one point at least this was the only way Debian (and I think an option on Gentoo) was distributed. We do have support for the pkg-config file as well. I don't know if any distros are still doing this

[rossburton]

FWIW Debian provides it as sources and a prebuilt library still, eg https://packages.debian.org/source/buster/googletest.

[rossburton]

Would it be feasible to respect the sys_root property instead of hardcoding /usr?