templates: Timestamp: add {before,after} methods

This allows for more fine-grained control of timestamp formatting, for
example:

```
[template-aliases]
'format_timestamp(timestamp)' = '''
if(timestamp.before("1 week ago"),
  timestamp.format("%b %d %Y %H:%M"),
  timestamp.ago()
)
'''
```

Closes #3782.

CHANGELOG.md

@@ -51,6 +51,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   The output can be customized via the `templates.annotate_commit_summary`
   config variable.
 
+* Timestamp objects in templates now have `after(date) -> Boolean` and
+  `before(date) -> Boolean` methods for comparing timestamps to other dates.
+
 ### Fixed bugs
 
 * Error on `trunk()` revset resolution is now handled gracefully.

cli/src/template_builder.rs

@@ -18,6 +18,7 @@ use itertools::Itertools as _;
 use jj_lib::backend::Signature;
 use jj_lib::backend::Timestamp;
 use jj_lib::dsl_util::AliasExpandError as _;
+use jj_lib::time_util::DatePattern;
 
 use crate::template_parser;
 use crate::template_parser::BinaryOp;
@@ -900,6 +901,24 @@ fn builtin_timestamp_methods<'a, L: TemplateLanguage<'a> + ?Sized>(
             Ok(L::wrap_timestamp(out_property))
         },
     );
+    map.insert(
+        "after",
+        |_language, _diagnostics, _build_ctx, self_property, function| {
+            let [date_pattern_node] = function.expect_exact_arguments()?;
+            let now = chrono::offset::Local::now();
+            let date_pattern = template_parser::expect_string_literal_with(
+                date_pattern_node,
+                |date_pattern, span| {
+                    DatePattern::from_str_kind(date_pattern, function.name, now)
+                        .map_err(|_| TemplateParseError::expression("Invalid date pattern", span))
+                },
+            )?;
+            let out_property =
+                self_property.and_then(move |timestamp| Ok(date_pattern.matches(&timestamp)));
+            Ok(L::wrap_boolean(out_property))
+        },
+    );
+    map.insert("before", map["after"]);
     map
 }
 

cli/tests/test_commit_template.rs

@@ -146,6 +146,29 @@ fn test_log_author_timestamp_local() {
     "###);
 }
 
+#[test]
+fn test_log_author_timestamp_after_before() {
+    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, &["describe", "-m", "first"]);
+
+    let template = r#"
+    separate(" ",
+      author.timestamp(),
+      ":",
+      if(author.timestamp().after("1969"), "(after 1969)", "(before 1969)"),
+      if(author.timestamp().before("1975"), "(before 1975)", "(after 1975)"),
+      if(author.timestamp().before("now"), "(before now)", "(after now)")
+    ) ++ "\n""#;
+    let stdout = test_env.jj_cmd_success(&repo_path, &["log", "--no-graph", "-T", template]);
+    insta::assert_snapshot!(stdout, @r#"
+    2001-02-03 04:05:08.000 +07:00 : (after 1969) (after 1975) (before now)
+    1970-01-01 00:00:00.000 +00:00 : (after 1969) (before 1975) (before now)
+    "#);
+}
+
 #[test]
 fn test_mine_is_true_when_author_is_user() {
     let test_env = TestEnvironment::default();

docs/templates.md

@@ -265,6 +265,8 @@ The following methods are defined.
   format string](https://docs.rs/chrono/latest/chrono/format/strftime/).
 * `.utc() -> Timestamp`: Convert timestamp into UTC timezone.
 * `.local() -> Timestamp`: Convert timestamp into local timezone.
+* `.after(date: String) -> Boolean`: True if the timestamp is exactly at or after the given date.
+* `.before(date: String) -> Boolean`: True if the timestamp is before, but not including, the given date.
 
 ### TimestampRange type