Make persistent tasks an optional feature

crates/daemon/src/args.rs

@@ -159,6 +159,13 @@ pub struct FeatureArgs {
         help = "Enable flyweight types. Flyweights are a lightweight, object delegate"
     )]
     pub flyweight_type: Option<bool>,
+
+    #[arg(
+        long,
+        help = "Enable persistent tasks, which persist the state of suspended/forked tasks between restarts. \
+                Note that this is the default behaviour in LambdaMOO."
+    )]
+    pub persistent_tasks: Option<bool>,
 }
 
 impl FeatureArgs {
@@ -178,6 +185,9 @@ impl FeatureArgs {
         if let Some(args) = self.flyweight_type {
             config.flyweight_type = args;
         }
+        if let Some(args) = self.persistent_tasks {
+            config.persistent_tasks = args;
+        }
     }
 }
 #[derive(Parser, Debug)]

crates/daemon/src/main.rs

@@ -21,6 +21,7 @@ use ed25519_dalek::SigningKey;
 use eyre::Report;
 use moor_db::{Database, TxDB};
 use moor_kernel::tasks::scheduler::Scheduler;
+use moor_kernel::tasks::{NoopTasksDb, TasksDb};
 use moor_kernel::textdump::textdump_load;
 use pem::Pem;
 use rand::rngs::OsRng;
@@ -149,7 +150,11 @@ fn main() -> Result<(), Report> {
         }
     }
 
-    let (tasks_db, _) = tasks_fjall::FjallTasksDB::open(&args.tasks_db);
+    let tasks_db: Box<dyn TasksDb> = if config.features_config.persistent_tasks {
+        Box::new(tasks_fjall::FjallTasksDB::open(&args.tasks_db).0)
+    } else {
+        Box::new(NoopTasksDb {})
+    };
 
     // We have to create the RpcServer before starting the scheduler because we need to pass it in
     // as a parameter to the scheduler for background session construction.
@@ -173,7 +178,7 @@ fn main() -> Result<(), Report> {
     let scheduler = Scheduler::new(
         version,
         database,
-        Box::new(tasks_db),
+        tasks_db,
         config.clone(),
         rpc_server.clone(),
     );

crates/kernel/src/config.rs

@@ -32,6 +32,9 @@ pub struct Config {
 
 #[derive(Clone, Debug, Serialize, Deserialize, Eq, PartialEq)]
 pub struct FeaturesConfig {
+    /// Whether to host a tasks DB and persist the state of suspended/forked tasks between restarts.
+    /// Note that this is the default behaviour in LambdaMOO.
+    pub persistent_tasks: bool,
     /// Whether to allow notify() to send arbitrary MOO common to players. The interpretation of
     /// the common varies depending on host/client.
     /// If this is false, only strings are allowed, as in LambdaMOO.
@@ -51,6 +54,7 @@ pub struct FeaturesConfig {
 impl Default for FeaturesConfig {
     fn default() -> Self {
         Self {
+            persistent_tasks: true,
             rich_notify: true,
             lexical_scopes: true,
             map_type: true,
@@ -69,16 +73,24 @@ impl FeaturesConfig {
         }
     }
 
-    /// Returns true if the configuration is backwards compatible with LambdaMOO 1.8 features.
+    /// Returns true if the configuration is backwards compatible with LambdaMOO 1.8 features
     pub fn is_lambdammoo_compatible(&self) -> bool {
-        !self.lexical_scopes && !self.map_type && !self.type_dispatch && !self.flyweight_type
+        !self.lexical_scopes
+            && !self.map_type
+            && !self.type_dispatch
+            && !self.flyweight_type
+            && !self.rich_notify
+            && self.persistent_tasks
     }
 
-    /// Returns true if the configuration is compatible with another configuration.
+    /// Returns true if the configuration is compatible with another configuration, for the pur
+    /// poses of textdump loading
     /// Which means that if the other configuration has a feature enabled, this configuration
     /// must also have it enabled.
     /// The other way around is fine.
-    pub fn is_compatible(&self, other: &FeaturesConfig) -> bool {
+    pub fn is_textdump_compatible(&self, other: &FeaturesConfig) -> bool {
+        // Note that tasks/rich_notify are not included in this check, as they do not affect
+        // the database format.
         (!other.lexical_scopes || self.lexical_scopes)
             && (!other.map_type || self.map_type)
             && (!other.type_dispatch || self.type_dispatch)

crates/kernel/src/textdump/load_textdump.rs

@@ -133,7 +133,7 @@ pub fn read_textdump<T: io::Read>(
             }
 
             // Features mut be compatible
-            if !features_config.is_compatible(features) {
+            if !features_config.is_textdump_compatible(features) {
                 return Err(TextdumpReaderError::VersionError(
                     "Incompatible features".to_string(),
                 ));