Add --version command (#6)

Signed-off-by: James Sturtevant <jsturtevant@gmail.com>

Author: jsturtevant

build.rs

@@ -0,0 +1,34 @@
+use std::process::Command;
+
+fn main() {
+    let git_hash = Command::new("git")
+        .args(["describe", "--always", "--dirty"])
+        .output()
+        .map(|output| {
+            if output.status.success() {
+                String::from_utf8_lossy(&output.stdout).trim().to_string()
+            } else {
+                "unknown".to_string()
+            }
+        })
+        .unwrap_or_else(|_| "unknown".to_string());
+
+    let git_date = Command::new("git")
+        .args(["log", "-1", "--format=%cs"])
+        .output()
+        .map(|output| {
+            if output.status.success() {
+                String::from_utf8_lossy(&output.stdout).trim().to_string()
+            } else {
+                "unknown".to_string()
+            }
+        })
+        .unwrap_or_else(|_| "unknown".to_string());
+
+    // Make the git info available to the program
+    println!("cargo:rustc-env=GIT_HASH={}", git_hash);
+    println!("cargo:rustc-env=GIT_DATE={}", git_date);
+
+    // Re-run build script if git HEAD changes
+    println!("cargo:rerun-if-changed=.git/HEAD");
+}

src/main.rs

@@ -2,7 +2,16 @@ use std::env;
 
 use cargo_hyperlight::cargo;
 
+const VERSION: &str = env!("CARGO_PKG_VERSION");
+const GIT_HASH: &str = env!("GIT_HASH");
+const GIT_DATE: &str = env!("GIT_DATE");
+
 fn main() {
+    if env::args().any(|arg| arg == "--version" || arg == "-V") {
+        println!("cargo-hyperlight {} ({} {})", VERSION, GIT_HASH, GIT_DATE);
+        return;
+    }
+
     let args = env::args_os().enumerate().filter_map(|(i, arg)| {
         // skip the binary name and the "hyperlight" subcommand if present
         if i == 0 || (i == 1 && arg == "hyperlight") {