templates: add .normal_hex() for {Commit,Change}Id

This doesn't do much for CommitId but outputs the "forward" hex for
ChangeId, which can be useful to use as Gerrit Change-Id.

CHANGELOG.md

@@ -62,6 +62,8 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 * `jj squash`: the `-k` flag can be used as a shorthand for `--keep-emptied`.
 
+* CommitId / ChangeId template types now support `.normal_hex()`.
+
 ### Fixed bugs
 
  * Fixed panic when parsing invalid conflict markers of a particular form.

cli/src/commit_templater.rs

@@ -1225,6 +1225,21 @@ fn builtin_commit_or_change_id_methods<'repo>(
     // Not using maplit::hashmap!{} or custom declarative macro here because
     // code completion inside macro is quite restricted.
     let mut map = CommitTemplateBuildMethodFnMap::<CommitOrChangeId>::new();
+    map.insert(
+        "normal_hex",
+        |_language, _build_ctx, self_property, function| {
+            function.expect_no_arguments()?;
+            Ok(L::wrap_string(self_property.map(|id| {
+                // Note: this is _not_ the same as id.hex() for ChangeId, which
+                // returns the "reverse" hex (z-k), instead of the "forward" /
+                // normal hex (0-9a-f) we want here.
+                match id {
+                    CommitOrChangeId::Commit(id) => id.hex(),
+                    CommitOrChangeId::Change(id) => id.hex(),
+                }
+            })))
+        },
+    );
     map.insert("short", |language, build_ctx, self_property, function| {
         let ([], [len_node]) = function.expect_arguments()?;
         let len_property = len_node

cli/tests/test_commit_template.rs

@@ -643,6 +643,56 @@ fn test_log_git_head() {
     "###);
 }
 
+#[test]
+fn test_log_commit_id_normal_hex() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    test_env.jj_cmd_ok(&repo_path, &["new", "-m", "first"]);
+    test_env.jj_cmd_ok(&repo_path, &["new", "-m", "second"]);
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "log",
+            "-T",
+            r#"commit_id ++ ": " ++ commit_id.normal_hex()"#,
+        ],
+    );
+    insta::assert_snapshot!(stdout, @r#"
+    @  6572f22267c6f0f2bf7b8a37969ee5a7d54b8aae: 6572f22267c6f0f2bf7b8a37969ee5a7d54b8aae
+    ○  222fa9f0b41347630a1371203b8aad3897d34e5f: 222fa9f0b41347630a1371203b8aad3897d34e5f
+    ○  230dd059e1b059aefc0da06a2e5a7dbf22362f22: 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    ◆  0000000000000000000000000000000000000000: 0000000000000000000000000000000000000000
+    "#);
+}
+
+#[test]
+fn test_log_change_id_normal_hex() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    test_env.jj_cmd_ok(&repo_path, &["new", "-m", "first"]);
+    test_env.jj_cmd_ok(&repo_path, &["new", "-m", "second"]);
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "log",
+            "-T",
+            r#"change_id ++ ": " ++ change_id.normal_hex()"#,
+        ],
+    );
+    insta::assert_snapshot!(stdout, @r#"
+    @  kkmpptxzrspxrzommnulwmwkkqwworpl: ffdaa62087a280bddc5e3d3ff933b8ae
+    ○  rlvkpnrzqnoowoytxnquwvuryrwnrmlp: 8e4fac809cbb3b162c953458183c8dea
+    ○  qpvuntsmwlqtpsluzzsnyyzlmlwvmlnu: 9a45c67d3e96a7e5007c110ede34dec5
+    ◆  zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz: 00000000000000000000000000000000
+    "#);
+}
+
 #[test]
 fn test_log_customize_short_id() {
     let test_env = TestEnvironment::default();

docs/templates.md

@@ -105,6 +105,8 @@ This type cannot be printed. The following methods are defined.
 
 The following methods are defined.
 
+* `.normal_hex() -> String`: Normal hex representation (0-9a-f), useful for
+  ChangeId, whose canonical hex representation is "reversed" (z-k).
 * `.short([len: Integer]) -> String`
 * `.shortest([min_len: Integer]) -> ShortestIdPrefix`: Shortest unique prefix.