Detect when -lz doesn't work and compile zlib from source

[alexcrichton]

We've got all the sources on hand! We should detect this failure mode and defer to build_zlib()

[alexcrichton]

@evhub if you're willing to write up a patch for this I'd love to review!

[cssivision]

i think i can fire a pr to fix this. @alexcrichton

[alexcrichton]

Awesome, thanks! Let me know if you have any questions

[cssivision]

it seems that i have made a mistake, i try to detect libz.so using crate pkg-config with:

// try this
pkg_config::find_library("zlib").is_ok() 
// also this
pkg_config::find_library("z").is_ok()

without installing zlib-dev they both return false, after install zlib-dev also return false.
it seems pkg-config is not work for this lib, finally i found the dynamic lib in path /lib/x86_64-linux-gnu/libz.so.1, zlib1g-dev package in ubuntu 14.04 does not contain pkg-config file zlib.pc.

i will dive into crate pkg-config,try to found the solution, @alexcrichton any suggestions?

[cssivision]

it has nothing to do with pkg-config. it's a exception in ubuntu 14.04, there is no default libz.so installed, in centos 7 there exists libz.so, without zlib-devel installed, also can build this crate, but pkg_config::find_library("zlib").is_ok() will return false, after installing zlib-devel, pkg_config::find_library("zlib").is_ok() will return true.

but ubuntu 14.04 will always return false, because zlib1g-dev package in ubuntu 14.04 does not contain pkg-config file zlib.pc, build from source may fix this. in other linux distro which exists libz.so, but without zlib-devel will also build from source code which is not necessary.

[alexcrichton]

Ah yeah the reason there's a fallback of just printing rustc-link-lib=z is because it seemed common at the time to find libz.so without having pkg-config installed. I think what we may want to do is to just try compilling a simple C file with -lz and see if it compiles and links correctly. If that fails we'd fall back to build_zlib()

[cssivision]

like this?

let out = env::var("OUT_DIR").unwrap();
let p = Path::new(&out).join("foo.c");
let mut f = File::open(&p).unwrap();
f.write_all(b"#include <zlib.h>\nint foo()\n{\n    return 0;\n}").unwrap();
gcc::Config::new()
    .file(Path::new(&out).join("foo.c"))
    .flag("-lz")
    .try_compile("libfoo.a");

[alexcrichton]

Ah unfortunately that won't actually invoke the linker, so it won't detect the failure. I think it's fine though to use gcc's get_compiler method and then use that to invoke the compiler manually?

[cssivision]

yes, use get_compiler().to_command().exec() does the trick. but i finally find that pkg_config::probe_linrary("zlib").is_ok() works for ubuntu 14.04. it turns out that there is something wrong with the my server. built from a new ubuntu 14.04 server, everything is just ok.

find libz.so without having pkg-config installed is nice, but in the build.rs we have imported crate pkg_config, i prefer using pkg_config. @alexcrichton which one do you prefer? using get_compiler will have to wait gcc-rs release version which contains try_get_compiler function, or get_compiler may be panic.

[alexcrichton]

Ah sorry for the delay! @cssivision I think we already use pkg_config, right? Is there a different invocation you're thinking of?

[BusyJay]

Why not just compiling from sources and link to system library when required? So we can get a consistent binary (always link to the same version of zlib) by default no matter whether zlib is installed on host or not.