Extensions registering tasks (#9572)

This PR also introduces built-in tasks for Rust and Elixir. Note that
this is not a precedent for future PRs to include tasks for more
languages; we simply want to find the rough edges with tasks & language
integrations before proceeding to task contexts provided by extensions.

As is, we'll load tasks for all loaded languages, so in order to get
Elixir tasks, you have to open an Elixir buffer first. I think it sort
of makes sense (though it's not ideal), as in the future where
extensions do provide their own tasks.json, we'd like to limit the # of
tasks surfaced to the user to make them as relevant to the project at
hand as possible.

Release Notes:

- Added built-in tasks for Rust and Elixir files.

crates/task/src/static_source.rs

@@ -19,17 +19,46 @@ struct StaticTask {
     definition: Definition,
 }
 
+impl StaticTask {
+    fn new(definition: Definition, (id_base, index_in_file): (&str, usize)) -> Arc<Self> {
+        Arc::new(Self {
+            id: TaskId(format!(
+                "static_{id_base}_{index_in_file}_{}",
+                definition.label
+            )),
+            definition,
+        })
+    }
+}
+
+/// TODO: doc
+pub fn tasks_for(tasks: TaskDefinitions, id_base: &str) -> Vec<Arc<dyn Task>> {
+    tasks
+        .0
+        .into_iter()
+        .enumerate()
+        .map(|(index, task)| StaticTask::new(task, (id_base, index)) as Arc<_>)
+        .collect()
+}
+
 impl Task for StaticTask {
     fn exec(&self, cx: TaskContext) -> Option<SpawnInTerminal> {
-        let TaskContext { cwd, env } = cx;
+        let TaskContext {
+            cwd,
+            task_variables,
+        } = cx;
         let cwd = self
             .definition
             .cwd
             .clone()
-            .and_then(|path| subst::substitute(&path, &env).map(Into::into).ok())
+            .and_then(|path| {
+                subst::substitute(&path, &task_variables.0)
+                    .map(Into::into)
+                    .ok()
+            })
             .or(cwd);
         let mut definition_env = self.definition.env.clone();
-        definition_env.extend(env);
+        definition_env.extend(task_variables.0);
         Some(SpawnInTerminal {
             id: self.id.clone(),
             cwd,
@@ -58,15 +87,15 @@ impl Task for StaticTask {
 
 /// The source of tasks defined in a tasks config file.
 pub struct StaticSource {
-    tasks: Vec<StaticTask>,
-    _definitions: Model<TrackedFile<DefinitionProvider>>,
+    tasks: Vec<Arc<StaticTask>>,
+    _definitions: Model<TrackedFile<TaskDefinitions>>,
     _subscription: Subscription,
 }
 
 /// Static task definition from the tasks config file.
 #[derive(Clone, Default, Debug, PartialEq, Eq, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "snake_case")]
-pub(crate) struct Definition {
+pub struct Definition {
     /// Human readable name of the task to display in the UI.
     pub label: String,
     /// Executable command to spawn.
@@ -106,9 +135,9 @@ pub enum RevealStrategy {
 
 /// A group of Tasks defined in a JSON file.
 #[derive(Clone, Debug, Default, PartialEq, Eq, Serialize, Deserialize, JsonSchema)]
-pub struct DefinitionProvider(pub(crate) Vec<Definition>);
+pub struct TaskDefinitions(pub Vec<Definition>);
 
-impl DefinitionProvider {
+impl TaskDefinitions {
     /// Generates JSON schema of Tasks JSON definition format.
     pub fn generate_json_schema() -> serde_json_lenient::Value {
         let schema = SchemaSettings::draft07()
@@ -206,7 +235,7 @@ impl StaticSource {
     /// Initializes the static source, reacting on tasks config changes.
     pub fn new(
         id_base: impl Into<Cow<'static, str>>,
-        definitions: Model<TrackedFile<DefinitionProvider>>,
+        definitions: Model<TrackedFile<TaskDefinitions>>,
         cx: &mut AppContext,
     ) -> Model<Box<dyn TaskSource>> {
         cx.new_model(|cx| {
@@ -222,10 +251,7 @@ impl StaticSource {
                             .clone()
                             .into_iter()
                             .enumerate()
-                            .map(|(i, definition)| StaticTask {
-                                id: TaskId(format!("static_{id_base}_{i}_{}", definition.label)),
-                                definition,
-                            })
+                            .map(|(i, definition)| StaticTask::new(definition, (&id_base, i)))
                             .collect();
                         cx.notify();
                     }
@@ -247,9 +273,8 @@ impl TaskSource for StaticSource {
         _: &mut ModelContext<Box<dyn TaskSource>>,
     ) -> Vec<Arc<dyn Task>> {
         self.tasks
-            .clone()
-            .into_iter()
-            .map(|task| Arc::new(task) as Arc<dyn Task>)
+            .iter()
+            .map(|task| task.clone() as Arc<dyn Task>)
             .collect()
     }