4 files changed, 14 insertions, 13 deletions

diff --git a/src/executor.rs b/src/executor.rs
index 0d1a5a2..f3c5993 100644
--- a/src/executor.rs
+++ b/src/executor.rs
@@ -42,7 +42,7 @@ struct TaskMeta {
 	pub inherit: Vec<InputHash>,
 	pub depends: BTreeSet<OutputHash>,
 	pub input_hash: InputHash,
-	pub output_hash: OutputHash,
+	pub output_hash: Option<OutputHash>,
 }
 
 impl TaskMeta {
@@ -117,17 +117,18 @@ impl<'a> Executor<'a> {
 	fn task_deps(&self, task: &Task) -> BTreeSet<OutputHash> {
 		task.depends
 			.iter()
-			.map(|dep| self.tasks_done[dep].output_hash)
+			.filter_map(|dep| self.tasks_done[dep].output_hash)
 			.collect()
 	}
 
 	fn task_deps_with_actions(&self, task: &Task) -> HashMap<OutputHash, TaskAction> {
 		task.depends
 			.iter()
-			.map(|dep| {
-				let task = &self.tasks[&dep.id];
-				let meta = &self.tasks_done[dep];
-				(meta.output_hash, task.action.clone())
+			.filter_map(|dep| {
+				self.tasks_done[dep].output_hash.map(|output_hash| {
+					let task = &self.tasks[&dep.id];
+					(output_hash, task.action.clone())
+				})
 			})
 			.collect()
 	}
@@ -162,7 +163,7 @@ impl<'a> Executor<'a> {
 			TaskAction::Fetch { .. } => {
 				// Fetch tasks are not implemented yet,
 				// we just return the input hash
-				OutputHash(input_hash.0)
+				Some(OutputHash(input_hash.0))
 			}
 			TaskAction::Run(run) => {
 				let task = runner::Task {
diff --git a/src/runner/mod.rs b/src/runner/mod.rs
index 4710552..aff1d3e 100644
--- a/src/runner/mod.rs
+++ b/src/runner/mod.rs
@@ -16,5 +16,5 @@ pub struct Task {
 }
 
 pub trait Runner {
-	fn run(&self, task: &Task) -> Result<OutputHash>;
+	fn run(&self, task: &Task) -> Result<Option<OutputHash>>;
 }
diff --git a/src/runner/runc.rs b/src/runner/runc.rs
index 756fc28..98fee2a 100644
--- a/src/runner/runc.rs
+++ b/src/runner/runc.rs
@@ -20,7 +20,7 @@ use crate::{
 };
 
 #[derive(Debug, Deserialize, Serialize)]
-struct Request(runner::Task, ipc::IpcSender<Result<OutputHash>>);
+struct Request(runner::Task, ipc::IpcSender<Result<Option<OutputHash>>>);
 
 fn runner(idmap_finished: ipc::IpcReceiver<()>, channel: ipc::IpcReceiver<Request>) -> ! {
 	idmap_finished
@@ -95,7 +95,7 @@ impl RuncRunner {
 }
 
 impl super::Runner for RuncRunner {
-	fn run(&self, task: &runner::Task) -> Result<OutputHash> {
+	fn run(&self, task: &runner::Task) -> Result<Option<OutputHash>> {
 		let (reply_tx, reply_rx) = ipc::channel().expect("IPC channel creation failed");
 
 		self.channel
diff --git a/src/runner/runc/run.rs b/src/runner/runc/run.rs
index 3a1d9fc..bd32bdb 100644
--- a/src/runner/runc/run.rs
+++ b/src/runner/runc/run.rs
@@ -124,7 +124,7 @@ fn unpack_dependencies(task: &runner::Task) -> Result<()> {
 	Ok(())
 }
 
-fn collect_output(task: &runner::Task) -> Result<OutputHash> {
+fn collect_output(task: &runner::Task) -> Result<Option<OutputHash>> {
 	let source = paths::join(&[
 		&paths::task_tmp_dir(&task.input_hash),
 		paths::TASK_TMP_DEST_SUBDIR,
@@ -147,10 +147,10 @@ fn collect_output(task: &runner::Task) -> Result<OutputHash> {
 
 	util::fs::rename(filename, paths::output_filename(&hash))?;
 
-	Ok(hash)
+	Ok(Some(hash))
 }
 
-pub fn handle_task(task: runner::Task) -> Result<OutputHash> {
+pub fn handle_task(task: runner::Task) -> Result<Option<OutputHash>> {
 	init_task(&task).context("Failed to initialize task")?;
 	unpack_dependencies(&task).context("Failed to unpack dependencies")?;