Allow setting install prefix in build.rs via environment variable

[idealseal]

This would probably ease maintenance for distro maintainers.

This would require the wrapper variable to be joined with the prefix, something like

let prefix = std::env::var("BEAR_INSTALL_PREFIX").unwrap_or(DEFAULT_PREFIX);
let prefix = PathBuf::from(prefix);
...

Would you be open to such a patch?

@DarthGandalf would this help for the ebuild?

[DarthGandalf]

Yeah, something that would help. I'm currently using sed to replace the prefix https://cgit.gentoo.org/repo/gentoo.git/tree/dev-util/bear/bear-4.0.4.ebuild?id=4919d4c4328c51cb1a64a49068536e7e2bd75be6#n158

[idealseal]

Related to #668.

[rizsotto]

I'm 4.1 version I'm trying to do the relative path. (As described in #686.) That would remove the need for this.

Happy to hear some feedback on that plan from packagers before I implement it.

[DarthGandalf]

If the absolute path needs to be written to the wrapper, I don't see the difference vs current solution with the same path written in build.rs. At least, in my case the distinction between compiled/non-compiled is negligible.

From the description of #668 I think it was more about "portable" installation, where same exact binary works in either /usr/bin/bear, or in /opt/bear/bin/bear; so that the binary (or wrapper) would check in runtime its own path, and construct the path to the library (if to do that way, need to be careful with lib vs lib64 and multilib systems)

For my case such movability doesn't matter; I can pass the absolute path in either build.rs, or to this wrapper. But the current way (using sed) is somewhat fragile and can fail if the format of build.rs changes. So I'd slightly prefer a build-time config which doesn't require sed. E.g. in autoconf world it would be ./configure --prefix /path, in cmake it would be -DCMAKE_INSTALL_PREFIX=..., and I don't know if cargo has any common way to do this. Worst case, even a custom environment variable which build.rs reads (that is, in compile time), would work. That is what @idealseal suggested here. But if you do make it portable, then looks like I won't need to explicitly configure the absolute path anymore, and it should just work.

[DarthGandalf]

Actually, I didn't check if Bear handles multilib at all. At least, the gentoo ebuild of bear-4.0.4 doesn't install the 32-bit version of libexec.so on 64-bit system. I may need to fix that.