Add a version banner with git revision and build metadata (echo --version, startup log, CTCP VERSION)

build.rs

@@ -12,5 +12,61 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         .build_client(false)
         .compile_protos(&["proto/echo.proto"], &["proto"])?;
     println!("cargo:rerun-if-changed=proto/echo.proto");
+    emit_build_info();
     Ok(())
 }
+
+// Capture the git revision and build metadata at compile time and expose them as
+// `env!()`-readable vars, so the binary can print a real version banner (its own
+// commit hash, build date, toolchain). Degrades gracefully when git is absent
+// (a tarball build) — the fields just read "unknown"/empty.
+fn emit_build_info() {
+    use std::process::Command;
+    let git = |args: &[&str]| {
+        Command::new("git")
+            .args(args)
+            .output()
+            .ok()
+            .filter(|o| o.status.success())
+            .map(|o| String::from_utf8_lossy(&o.stdout).trim().to_string())
+            .filter(|s| !s.is_empty())
+    };
+    let hash = git(&["rev-parse", "--short=12", "HEAD"]).unwrap_or_else(|| "unknown".into());
+    let dirty = git(&["status", "--porcelain"]).map(|s| !s.is_empty()).unwrap_or(false);
+    let commit_date = git(&["log", "-1", "--format=%cd", "--date=short"]).unwrap_or_default();
+
+    // Build time (UTC seconds), honouring SOURCE_DATE_EPOCH for reproducible builds.
+    let epoch = std::env::var("SOURCE_DATE_EPOCH")
+        .ok()
+        .and_then(|s| s.parse::<u64>().ok())
+        .unwrap_or_else(|| {
+            std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .map(|d| d.as_secs())
+                .unwrap_or(0)
+        });
+    let rustc = std::env::var("RUSTC").unwrap_or_else(|_| "rustc".into());
+    let rustc_ver = Command::new(rustc)
+        .arg("--version")
+        .output()
+        .ok()
+        .map(|o| String::from_utf8_lossy(&o.stdout).trim().to_string())
+        .filter(|s| !s.is_empty())
+        .unwrap_or_else(|| "unknown".into());
+
+    println!("cargo:rustc-env=ECHO_GIT_HASH={hash}");
+    println!("cargo:rustc-env=ECHO_GIT_DIRTY={}", if dirty { "-dirty" } else { "" });
+    println!("cargo:rustc-env=ECHO_COMMIT_DATE={commit_date}");
+    println!("cargo:rustc-env=ECHO_BUILD_EPOCH={epoch}");
+    println!("cargo:rustc-env=ECHO_RUSTC={rustc_ver}");
+    println!("cargo:rustc-env=ECHO_TARGET={}", std::env::var("TARGET").unwrap_or_default());
+
+    // Re-run (refresh the hash) when the checked-out commit moves.
+    println!("cargo:rerun-if-changed=.git/HEAD");
+    if let Ok(head) = std::fs::read_to_string(".git/HEAD") {
+        if let Some(reference) = head.strip_prefix("ref: ").map(str::trim) {
+            println!("cargo:rerun-if-changed=.git/{reference}");
+        }
+    }
+    println!("cargo:rerun-if-env-changed=SOURCE_DATE_EPOCH");
+}