settings: parse TOML date-time value as well as string timestamp

We can usually omit quotes in --config=NAME=VALUE, but an RFC3339 string is a
valid TOML date-time expression. It's weird that quoting is required to specify
a date-time value.

cli/tests/test_revset_output.rs

@@ -740,7 +740,7 @@ fn test_revset_committer_date_with_time_zone() {
     test_env.jj_cmd_ok(
         &repo_path,
         &[
-            "--config=debug.commit-timestamp='2023-01-25T11:30:00-05:00'",
+            "--config=debug.commit-timestamp=2023-01-25T11:30:00-05:00",
             "describe",
             "-m",
             "first",
@@ -749,7 +749,7 @@ fn test_revset_committer_date_with_time_zone() {
     test_env.jj_cmd_ok(
         &repo_path,
         &[
-            "--config=debug.commit-timestamp='2023-01-25T12:30:00-05:00'",
+            "--config=debug.commit-timestamp=2023-01-25T12:30:00-05:00",
             "new",
             "-m",
             "second",
@@ -758,7 +758,7 @@ fn test_revset_committer_date_with_time_zone() {
     test_env.jj_cmd_ok(
         &repo_path,
         &[
-            "--config=debug.commit-timestamp='2023-01-25T13:30:00-05:00'",
+            "--config=debug.commit-timestamp=2023-01-25T13:30:00-05:00",
             "new",
             "-m",
             "third",
@@ -768,7 +768,7 @@ fn test_revset_committer_date_with_time_zone() {
     let mut log_commits_before_and_after =
         |committer_date: &str, now: &str, tz: &str| -> (String, String) {
             test_env.add_env_var("TZ", tz);
-            let config = format!("debug.commit-timestamp='{now}'");
+            let config = format!("debug.commit-timestamp={now}");
             let before_log = test_env.jj_cmd_success(
                 &repo_path,
                 &[

lib/src/settings.rs

@@ -125,12 +125,17 @@ impl SignSettings {
 }
 
 fn to_timestamp(value: ConfigValue) -> Result<Timestamp, Box<dyn std::error::Error + Send + Sync>> {
-    // TODO: Maybe switch to native TOML date-time type?
+    // Since toml_edit::Datetime isn't the date-time type used across our code
+    // base, we accept both string and date-time types.
     if let Some(s) = value.as_str() {
         Ok(Timestamp::from_datetime(DateTime::parse_from_rfc3339(s)?))
+    } else if let Some(d) = value.as_datetime() {
+        // It's easier to re-parse the TOML date-time expression.
+        let s = d.to_string();
+        Ok(Timestamp::from_datetime(DateTime::parse_from_rfc3339(&s)?))
     } else {
         let ty = value.type_name();
-        Err(format!("invalid type: {ty}, expected a date-time string").into())
+        Err(format!("invalid type: {ty}, expected a date-time").into())
     }
 }
 

lib/tests/test_operations.rs

@@ -427,7 +427,7 @@ fn stable_op_id_settings() -> UserSettings {
     config.add_layer(
         ConfigLayer::parse(
             ConfigSource::User,
-            "debug.operation-timestamp = '2001-02-03T04:05:06+07:00'",
+            "debug.operation-timestamp = 2001-02-03T04:05:06+07:00",
         )
         .unwrap(),
     );