Make channel buffers configurable

Cargo.lock

@@ -2069,6 +2069,7 @@ version = "1.17.1"
 dependencies = [
  "color-eyre",
  "command-group",
+ "derive_builder",
  "dunce",
  "futures",
  "miette",

lib/Cargo.toml

@@ -21,6 +21,7 @@ thiserror = "1.0.26"
 tracing = "0.1.26"
 dunce = "1.0.2"
 futures = "0.3.16"
+derive_builder = "0.10.2"
 
 [dependencies.command-group]
 version = "1.0.5"

lib/src/config.rs

@@ -1,3 +1,37 @@
+use derive_builder::Builder;
+
+/// Configuration for [`Watchexec`][crate::Watchexec].
+///
+/// This is used both for constructing the instance and to reconfigure it at runtime, though note
+/// that some fields are only applied at construction time.
+///
+/// You should prefer the [`ConfigBuilder`] rather than using this directly. This struct is marked
+/// non-exhaustive such that new options may be added without breaking change.
+#[derive(Builder, Clone, Debug)]
+#[non_exhaustive]
+#[builder(build_fn(name = "finish"))]
 pub struct Config {
+	/// Working data for the filesystem event source.
+	///
+	/// This notably includes the path set to be watched.
+	#[builder(default)]
 	pub fs: crate::fs::WorkingData,
+
+	/// Internal: the buffer size of the channel which carries runtime errors.
+	///
+	/// The default (64) is usually fine. If you expect a much larger throughput of runtime errors,
+	/// adjusting this value may help. (Fixing whatever is causing the errors may also help.)
+	///
+	/// Only used at construction time, cannot be changed via reconfiguration.
+	#[builder(default = "64")]
+	pub error_channel_size: usize,
+
+	/// Internal: the buffer size of the channel which carries events.
+	///
+	/// The default (1024) is usually fine. If you expect a much larger throughput of events,
+	/// adjusting this value may help.
+	///
+	/// Only used at construction time, cannot be changed via reconfiguration.
+	#[builder(default = "1024")]
+	pub event_channel_size: usize,
 }

lib/src/lib.rs

@@ -24,10 +24,10 @@
 #![forbid(unsafe_code)]
 
 // the toolkit to make your own
+pub mod command;
 pub mod error;
 pub mod event;
 pub mod fs;
-pub mod command;
 pub mod signal;
 
 // the core experience

lib/src/watchexec.rs

@@ -1,4 +1,4 @@
-use std::sync::Arc;
+use std::{mem::take, sync::Arc};
 
 use futures::FutureExt;
 use tokio::{
@@ -22,16 +22,16 @@ pub struct Watchexec {
 }
 
 impl Watchexec {
-	pub fn new(config: Config) -> Result<Self, CriticalError> {
-		let (fs_s, fs_r) = watch::channel(config.fs);
+	pub fn new(mut config: Config) -> Result<Self, CriticalError> {
+		let (fs_s, fs_r) = watch::channel(take(&mut config.fs));
 
 		let notify = Arc::new(Notify::new());
 		let start_lock = notify.clone();
 		let handle = spawn(async move {
 			notify.notified().await;
 
-			let (er_s, er_r) = mpsc::channel(64); // TODO: configure?
-			let (ev_s, ev_r) = mpsc::channel(1024); // TODO: configure?
+			let (er_s, er_r) = mpsc::channel(config.error_channel_size);
+			let (ev_s, ev_r) = mpsc::channel(config.event_channel_size);
 
 			macro_rules! subtask {
 				($task:expr) => {