Enforce MagickWand version in build.rs

It is very easy to overlook the version of MagickWand mentioned in the
README, so make sure the build system enforces it.

Fixes #19

cargo test passes

CHANGELOG.md

@@ -3,6 +3,10 @@
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## [0.6.1] - 2016-10-16
+### Changed
+- MagickWand version enforced in `build.rs` script at build time.
+
 ## [0.6.0] - 2016-09-20
 ### Changed
 - Update to 0.19.0 version of rust-bindgen; rebuilds are much faster.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "magick_rust"
-version = "0.5.2"
+version = "0.6.1"
 authors = ["Nathan Fiedler <nathanfiedler@fastmail.fm>"]
 description = "Selection of Rust bindings for the ImageMagick library."
 homepage = "https://github.com/nlfiedler/magick-rust"

README.md

@@ -7,6 +7,8 @@ A somewhat safe Rust interface to the [ImageMagick](http://www.imagemagick.org/)
 * Rust (~latest release)
 * Cargo (~latest release)
 * ImageMagick (version 6.9)
+    - [Homebrew](http://brew.sh) and [FreeBSD](https://www.freebsd.org) provide this version
+    - Linux may require building ImageMagick from source
 * Clang (version 3.5 or higher)
     - Or whatever version is dictated by rust-bindgen
 * [rust-bindgen](https://github.com/Yamakaky/rust-bindgen) (version 0.19 or higher)

build.rs

@@ -45,7 +45,7 @@ fn run_bindgen(out_dir: String, bindings_path_str: &str) {
                 .arg("--exists")
                 .arg("MagickWand")
                 .status().unwrap().success() {
-        panic!("MagickWand library must be installed")
+        panic!("MagickWand library must be installed");
     }
 
     // Get the compiler flags for the MagickWand library.
@@ -116,7 +116,32 @@ fn run_bindgen(out_dir: String, bindings_path_str: &str) {
     std::fs::remove_file(&gen_h_path).expect("could not remove header file");
 }
 
+fn assert_mw_version() {
+    //
+    // So far there is only 6.9 and then 7.x, so comparing to 6.10 should
+    // work for now. Such a release may very well work, but we will have to
+    // look at that when the time comes.
+    //
+    if !Command::new("pkg-config")
+                .arg("--atleast-version=6.9")
+                .arg("MagickWand")
+                .status().unwrap().success() {
+        panic!("MagickWand version must be at least 6.9");
+    }
+    if !Command::new("pkg-config")
+                .arg("--max-version=6.10")
+                .arg("MagickWand")
+                .status().unwrap().success() {
+        panic!("MagickWand version must be no higher than 6.9");
+    }
+}
+
 fn main() {
+    //
+    // Assert that the appropriate version of MagickWand is installed,
+    // since we are very dependent on the particulars of MagickWand.
+    //
+    assert_mw_version();
     //
     // If the MagickWand bindings are missing, generate them using
     // rust-bindgen.