From dc19f3908644d2d49f0ca97ae60d1d6f825d5dc9 Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Sat, 30 Oct 2021 13:22:50 +0200
Subject: driver: skip submission of empty tasks

---
 crates/common/src/types.rs  |  2 +-
 crates/driver/src/driver.rs | 22 +++++++++++++++-------
 crates/driver/src/task.rs   |  6 ++++++
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/crates/common/src/types.rs b/crates/common/src/types.rs
index 14d8c16..120630c 100644
--- a/crates/common/src/types.rs
+++ b/crates/common/src/types.rs
@@ -43,7 +43,7 @@ pub struct Task {
 	pub outputs: HashMap<String, String>,
 }
 
-#[derive(Clone, Debug, Deserialize, Serialize)]
+#[derive(Clone, Debug, Deserialize, Serialize, Default)]
 pub struct TaskOutput {
 	pub input_hash: Option<InputHash>,
 	pub layer: Option<LayerHash>,
diff --git a/crates/driver/src/driver.rs b/crates/driver/src/driver.rs
index 375c567..bafba1b 100644
--- a/crates/driver/src/driver.rs
+++ b/crates/driver/src/driver.rs
@@ -266,8 +266,12 @@ impl<'ctx> Driver<'ctx> {
 		}
 	}
 
-	fn spawn_task(&self, task_ref: &TaskRef<'ctx>, runner: &Runner) -> Result<UnixStream> {
+	fn spawn_task(&self, task_ref: &TaskRef<'ctx>, runner: &Runner) -> Result<Option<UnixStream>> {
 		let task_def = &self.state.ctx[task_ref.id];
+		if task_def.action.is_empty() {
+			return Ok(None);
+		}
+
 		let task_deps = self.state.task_deps(task_ref)?;
 		let task_output = task_def
 			.output
@@ -302,15 +306,19 @@ impl<'ctx> Driver<'ctx> {
 			outputs: task_output,
 		};
 
-		Ok(runner.spawn(&task))
+		Ok(Some(runner.spawn(&task)))
 	}
 
 	fn run_task(&mut self, task_ref: TaskRef<'ctx>, runner: &Runner) -> Result<()> {
-		let socket = self.spawn_task(&task_ref, runner)?;
-		assert!(self
-			.tasks_running
-			.insert(socket.as_raw_fd(), (socket, task_ref))
-			.is_none());
+		if let Some(socket) = self.spawn_task(&task_ref, runner)? {
+			assert!(self
+				.tasks_running
+				.insert(socket.as_raw_fd(), (socket, task_ref))
+				.is_none());
+		} else {
+			println!("Skipping empty task {:#}", task_ref);
+			self.update_runnable(task_ref, TaskOutput::default());
+		}
 		Ok(())
 	}
 
diff --git a/crates/driver/src/task.rs b/crates/driver/src/task.rs
index fe9572c..6b9083b 100644
--- a/crates/driver/src/task.rs
+++ b/crates/driver/src/task.rs
@@ -63,6 +63,12 @@ pub struct Action {
 	pub run: String,
 }
 
+impl Action {
+	pub fn is_empty(&self) -> bool {
+		self.run.is_empty()
+	}
+}
+
 #[derive(Clone, Debug, Deserialize)]
 pub struct TaskDef {
 	#[serde(skip)]
-- 
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