build.rs

// This build script expects the Gmsh development library is installed.
//
// Rationale:
//   This is the recommended way to write build scripts, (without network access).
//
// Downsides:
//   Running this crate without Gmsh installed causes a scary linker error.
//   At this point, users may get discouraged and give up.
//
//   Downloading tarballs is the recommended way to get the Gmsh SDK.
//
// Discarded options:
//
// 1. Bundling the Gmsh source code in this crate. Gmsh is 30MB compressed,
//    and crates.io has a 10MB limit.
// 2. Downloading a tarball from gmsh.info/bin.
//
// Build process:
//
// 1. Check for the environment variable GMSH_LIB_DIR.
// 2. Look for the Gmsh library in conventional system locations (and hope
//    the package manager has it available.
//
// -- script adapted from Kornel Lesiński's libpng build script:
//    https://github.com/kornelski/rust-libpng-sys/blob/master/build.rs

extern crate pkg_config;

use std::env;
use std::path::{Path, PathBuf};

fn main() {

    // 1. environment variable takes first priority
    let env_gmsh = "GMSH_LIB_DIR";
    if let Some(lib_dir) = env::var_os(env_gmsh) {

        // rerun if changed
        println!("cargo:rerun-if-env-changed={}", env_gmsh);

        let lib_dir = Path::new(&lib_dir);
        let dylib_name = format!("{}gmsh{}",
                                 env::consts::DLL_PREFIX,
                                 env::consts::DLL_SUFFIX);
        if lib_dir.join(dylib_name).exists() ||
           lib_dir.join("gmsh.lib").exists() {
                println!("cargo:rustc-link-search={}", lib_dir.display());
                // blocked on https://github.com/rust-lang/cargo/issues/4895
                // println!("cargo:rustc-dynamic-link-search={}", lib_dir.display())
        } else {
            println!("cargo:warning={} is set to {:?}, but no shared library files were found there", env_gmsh, lib_dir);
        }
    }

    // 2. search system libraries
    //    -- try pkg-config on linux
    else {
        match try_pkgconfig() {
            Ok(link_paths) => { for path in link_paths.into_iter() {
                                    println!("cargo:rustc-link-search={}", path.display());
                                }
                              }
            Err(not_found) => { eprintln!("pkg-config couldn't find Gmsh library {}, ", not_found) }
        }
    }

    // always link the gmsh shared library at the end
    println!("cargo:rustc-link-lib=gmsh");
}

fn try_pkgconfig() -> Result<Vec<PathBuf>, String> {
    let mut pkg = pkg_config::Config::new();
    pkg.atleast_version("4.4"); 

    match pkg.probe("gmsh") {
        Ok(gmsh_lib) => Ok(gmsh_lib.link_paths), // println!("found it"); true},
        Err(err) => Err(err.to_string()), // println!("cargo:warning={}, shared Gmsh library wasn't found. false},
    }
}