cli version: Show date as part of the version next to the commit id

The date comes from the commiter date of the commit. This is so that
it's easy to tell at a glance how old a version is.

cli/build.rs

@@ -41,21 +41,31 @@ fn main() -> std::io::Result<()> {
     }
     println!("cargo:rerun-if-env-changed=NIX_JJ_GIT_HASH");
 
-    if let Some(git_hash) = get_git_hash() {
-        println!("cargo:rustc-env=JJ_VERSION={}-{}", version, git_hash);
+    if let Some((date, git_hash)) = get_git_date_and_hash() {
+        println!(
+            "cargo:rustc-env=JJ_VERSION={}-{}-{}",
+            version, date, git_hash
+        );
     } else {
         println!("cargo:rustc-env=JJ_VERSION={}", version);
     }
 
     Ok(())
 }
 
-fn get_git_hash() -> Option<String> {
+/// Return the committer date in YYYYMMDD format and the git hash
+fn get_git_date_and_hash() -> Option<(String, String)> {
     if let Some(nix_hash) = std::env::var("NIX_JJ_GIT_HASH")
         .ok()
         .filter(|s| !s.is_empty())
     {
-        return Some(nix_hash);
+        return Some(("nix".to_string(), nix_hash));
+    }
+
+    fn trim_and_split_on_vbar(bytes: &[u8]) -> (String, String) {
+        let s = str::from_utf8(bytes).unwrap().trim_end();
+        let (date, id) = s.split_once('|').unwrap();
+        (date.to_owned(), id.to_owned())
     }
     if let Ok(output) = Command::new("jj")
         .args([
@@ -64,19 +74,22 @@ fn get_git_hash() -> Option<String> {
             "log",
             "--no-graph",
             "-r=@-",
-            "-T=commit_id",
+            r#"-T=committer.timestamp().format("%Y%m%d") ++ "|" ++ commit_id"#,
         ])
         .output()
     {
         if output.status.success() {
-            return Some(String::from_utf8(output.stdout).unwrap());
+            return Some(trim_and_split_on_vbar(&output.stdout));
         }
     }
 
-    if let Ok(output) = Command::new("git").args(["rev-parse", "HEAD"]).output() {
+    if let Ok(output) = Command::new("git")
+        .args(["log", "-1", "--format=%cs|%H", "HEAD"])
+        .output()
+    {
         if output.status.success() {
-            let line = str::from_utf8(&output.stdout).unwrap();
-            return Some(line.trim_end().to_owned());
+            let (date, hash) = trim_and_split_on_vbar(&output.stdout);
+            return Some((date.replace('-', ""), hash));
         }
     }
 

cli/tests/test_global_opts.rs

@@ -14,6 +14,8 @@
 
 use std::ffi::OsString;
 
+use assert_matches::assert_matches;
+
 use crate::common::{get_stderr_string, TestEnvironment};
 
 pub mod common;
@@ -67,10 +69,11 @@ fn test_no_subcommand() {
 
     let stdout = test_env.jj_cmd_success(test_env.env_root(), &["--version"]);
     let sanitized = stdout.replace(|c: char| c.is_ascii_hexdigit(), "?");
-    assert!(
-        sanitized == "jj ?.?.?\n"
-            || sanitized == "jj ?.?.?-????????????????????????????????????????\n",
-        "{sanitized}"
+    assert_matches!(
+        sanitized.as_str(),
+        "jj ?.?.?\n"
+            | "jj ?.?.?-????????-????????????????????????????????????????\n"
+            | "jj ?.?.?-nix-????????????????????????????????????????\n"
     );
 
     let stdout = test_env.jj_cmd_success(test_env.env_root(), &["-R", "repo"]);