Auto-get GIT_HASH when possible

build.rs

@@ -0,0 +1,56 @@
+use std::{path::Path, process::Command};
+
+fn main() {
+    // Specify re-run conditions
+
+    // 1. Rerun build script if we pass a new GIT_HASH
+    println!("cargo:rerun-if-env-changed=GIT_HASH");
+
+    // 2. Only do git based reruns if git directory exists
+    if Path::new(".git").exists() {
+        // If we change the branch, rerun
+        println!("cargo:rerun-if-changed=.git/HEAD");
+        if let Ok(r) = std::fs::read_to_string(".git/HEAD") {
+            if let Some(stripped) = r.strip_prefix("ref: ") {
+                // If the HEAD is detached it will be a commit hash
+                // so the HEAD changed directive above will pick it up,
+                // otherwise it will point to a ref in the refs directory
+                println!("cargo:rerun-if-changed=.git/{}", stripped);
+            }
+        }
+    }
+
+    // Getting git hash
+
+    // Don't fetch git hash if it's already in the ENV
+    let existing = std::env::var("GIT_HASH").unwrap_or_else(|_| String::new());
+    if !existing.is_empty() {
+        return;
+    }
+
+    // Get git hash from git and don't do anything if the command fails
+    if let Some(rev_parse) = cmd("git", &["rev-parse", "--short", "HEAD"]) {
+        // Add (dirty) to the GIT_HASH if the git status isn't clean
+        // This includes untracked files
+        let dirty = cmd("git", &["status", "--short"]).expect("git command works");
+
+        let git_hash = if dirty.is_empty() {
+            rev_parse
+        } else {
+            format!("{}(dirty)", rev_parse.trim())
+        };
+
+        println!("cargo:rustc-env=GIT_HASH={}", git_hash.trim());
+    }
+}
+
+// Helper function, Command is verbose...
+fn cmd(name: &str, args: &[&str]) -> Option<String> {
+    Command::new(name).args(args).output().ok().and_then(|o| {
+        if o.status.success() {
+            String::from_utf8(o.stdout).ok()
+        } else {
+            None
+        }
+    })
+}