operations: allow overriding timestamps for tests

It would be nice to be able to use snapshot testing and not have to
parse the output of `jj op log`. This patch lets us do that by
providing a new environment variable and config for overriding the
timestamps. Unlike `operation.hostname` and `operation.username`,
these are only meant for tests.

lib/src/settings.rs

@@ -29,15 +29,19 @@ pub struct RepoSettings {
     _config: config::Config,
 }
 
-impl UserSettings {
-    pub fn from_config(config: config::Config) -> Self {
-        let timestamp = match config.get_string("user.timestamp") {
+fn get_timestamp_config(config: &config::Config, key: &str) -> Option<Timestamp> {
+    match config.get_string(key) {
         Ok(timestamp_str) => match DateTime::parse_from_rfc3339(&timestamp_str) {
             Ok(datetime) => Some(Timestamp::from_datetime(datetime)),
             Err(_) => None,
         },
         Err(_) => None,
-        };
+    }
+}
+
+impl UserSettings {
+    pub fn from_config(config: config::Config) -> Self {
+        let timestamp = get_timestamp_config(&config, "user.timestamp");
         UserSettings { config, timestamp }
     }
 
@@ -88,6 +92,10 @@ impl UserSettings {
         "(no email configured)"
     }
 
+    pub fn operation_timestamp(&self) -> Option<Timestamp> {
+        get_timestamp_config(&self.config, "operation.timestamp")
+    }
+
     pub fn operation_hostname(&self) -> String {
         self.config
             .get_string("operation.hostname")

lib/src/transaction.rs

@@ -28,6 +28,7 @@ pub struct Transaction {
     repo: Option<MutableRepo>,
     parent_ops: Vec<Operation>,
     op_metadata: OperationMetadata,
+    end_time: Option<Timestamp>,
 }
 
 impl Transaction {
@@ -38,10 +39,12 @@ impl Transaction {
     ) -> Transaction {
         let parent_ops = vec![mut_repo.base_repo().operation().clone()];
         let op_metadata = create_op_metadata(user_settings, description.to_string());
+        let end_time = user_settings.operation_timestamp();
         Transaction {
             repo: Some(mut_repo),
             parent_ops,
             op_metadata,
+            end_time,
         }
     }
 
@@ -97,7 +100,7 @@ impl Transaction {
         let index = base_repo.index_store().write_index(mut_index).unwrap();
 
         let view_id = base_repo.op_store().write_view(view.store_view()).unwrap();
-        self.op_metadata.end_time = Timestamp::now();
+        self.op_metadata.end_time = self.end_time.unwrap_or_else(Timestamp::now);
         let parents = self.parent_ops.iter().map(|op| op.id().clone()).collect();
         let store_operation = op_store::Operation {
             view_id,
@@ -119,7 +122,9 @@ impl Transaction {
 }
 
 pub fn create_op_metadata(user_settings: &UserSettings, description: String) -> OperationMetadata {
-    let start_time = Timestamp::now();
+    let start_time = user_settings
+        .operation_timestamp()
+        .unwrap_or_else(Timestamp::now);
     let end_time = start_time.clone();
     let hostname = user_settings.operation_hostname();
     let username = user_settings.operation_username();

src/config.rs

@@ -78,6 +78,9 @@ fn env_overrides() -> config::Config {
     if let Ok(value) = env::var("JJ_TIMESTAMP") {
         builder = builder.set_override("user.timestamp", value).unwrap();
     }
+    if let Ok(value) = env::var("JJ_OP_TIMESTAMP") {
+        builder = builder.set_override("operation.timestamp", value).unwrap();
+    }
     if let Ok(value) = env::var("JJ_OP_HOSTNAME") {
         builder = builder.set_override("operation.hostname", value).unwrap();
     }

tests/common/mod.rs

@@ -72,6 +72,7 @@ impl TestEnvironment {
         cmd.env("JJ_TIMESTAMP", timestamp.to_rfc3339());
         cmd.env("JJ_USER", "Test User");
         cmd.env("JJ_EMAIL", "test.user@example.com");
+        cmd.env("JJ_OP_TIMESTAMP", timestamp.to_rfc3339());
         cmd.env("JJ_OP_HOSTNAME", "host.example.com");
         cmd.env("JJ_OP_USERNAME", "test-username");
         cmd