improvements

build.rs

@@ -0,0 +1,35 @@
+fn main() {
+    // Always rerun.
+
+    let version = if let Ok(commit) = try_get_commit() {
+        match has_no_changes() {
+            Ok(true) => commit,
+            Ok(false) => format!("{commit} (*)"),
+            Err(_) => format!("{commit} (?)"),
+        }
+    } else {
+        "unknown".into()
+    };
+
+    println!("cargo:rustc-env=GIT_COMMIT={version}");
+}
+
+fn try_get_commit() -> color_eyre::Result<String> {
+    let stdout = std::process::Command::new("git")
+        .arg("rev-parse")
+        .arg("HEAD")
+        .output()?
+        .stdout;
+
+    let stdout = String::from_utf8(stdout)?;
+
+    Ok(stdout.trim()[0..8].to_owned())
+}
+
+fn has_no_changes() -> color_eyre::Result<bool> {
+    Ok(std::process::Command::new("git")
+        .args(["diff", "--no-ext-diff", "--quiet", "--exit-code"])
+        .output()?
+        .status
+        .success())
+}