Merge pull request #5 from golddranks/master

Added support for pkg-config

Cargo.toml

@@ -11,5 +11,8 @@ build = "build.rs"
 [lib]
 name = "pq_sys"
 
+[build-dependencies]
+pkg-config = "~0.3"
+
 [dependencies]
 libc = "0.2.*"

README.md

@@ -10,11 +10,20 @@ This repository contains direct, one-to-one mappings to the C functions provided
 in `libpq-fe.h` and `postgres_ext.h`. This library expects that libpq be
 installed on the system.
 
-You may need to specify the environment variable `LIB_PQ_DIR` to the location of
-your postgresql lib directory if the build fails.
+The build script of crate will attempt to find the lib path of libpq using the
+following methods:
+
+* First, if the environment variable `LIB_PQ_DIR` is set, it will use its value
+* If the environment variable isn't set, it tries to use pkg-config to locate it.
+All the config options, such as `PKG_CONFIG_ALLOW_CROSS`, `PKG_CONFIG_ALL_STATIC`
+etc., of the crate [pkg-config](http://alexcrichton.com/pkg-config-rs/pkg_config/index.html)
+apply.
+* If it still can't locate the library, it will invoke the Postgres command
+`pg_config --libdir`
 
 The build script instructs Cargo to link the library statically if the environmental
 variable `LIB_PQ_STATIC` is set. This can be useful, if targeting for a musl target.
+If pkg-config is being used, it's configuration options will apply.
 
 For OSX 10.11 you can use brew to install postgresql and then set the
 environment variable as described below:

build.rs

@@ -1,11 +1,20 @@
+extern crate pkg_config;
+
 use std::fs;
 use std::path::PathBuf;
 use std::process::Command;
 use std::env;
 
 fn main() {
+    let link_flag = "pq";
+    let pkg_name = "libpq";
+
     if let Ok(lib_dir) = env::var("PQ_LIB_DIR") {
         println!("cargo:rustc-link-search=native={}", lib_dir);
+
+    } else if pkg_config::probe_library(pkg_name).is_ok() {
+        return // pkg_config does everything for us, including output for cargo
+
     } else if let Some(path) = pg_config_output() {
         let path = follow_dylib_symlinks(path.trim().into());
         println!("cargo:rustc-link-search=native={}", &path.display());
@@ -16,9 +25,8 @@ fn main() {
     } else {
         "dylib"
     };
-    let lib = "pq";
 
-    println!("cargo:rustc-link-lib={}={}", mode, lib);
+    println!("cargo:rustc-link-lib={}={}", mode, link_flag);
 }
 
 fn pg_config_output() -> Option<String> {