File watch events: Add dynamic wait period before writing new changes (#12585)

Cargo.lock

@@ -1944,6 +1944,7 @@ dependencies = [
  "countme",
  "crossbeam",
  "ctrlc",
+ "filetime",
  "notify",
  "rayon",
  "red_knot_module_resolver",

crates/red_knot/Cargo.toml

@@ -27,6 +27,7 @@ notify = { workspace = true }
 rayon = { workspace = true }
 rustc-hash = { workspace = true }
 salsa = { workspace = true }
+filetime = { workspace = true }
 tracing = { workspace = true }
 tracing-subscriber = { workspace = true }
 tracing-tree = { workspace = true }

crates/red_knot/tests/file_watching.rs

@@ -3,6 +3,7 @@
 use std::time::Duration;
 
 use anyhow::{anyhow, Context};
+use filetime::FileTime;
 use salsa::Setter;
 
 use red_knot::db::RootDatabase;
@@ -184,12 +185,24 @@ where
 }
 
 /// The precision of the last modified time is platform dependent and not arbitrarily precise.
-/// This method sets the current thread to sleep for a duration that
+/// This method sleeps until the last modified time of a newly created file changes. This guarantees
-/// is larger than the [last-modified precision on all platforms](https://doc.rust-lang.org/nightly/std/time/struct.SystemTime.html#platform-specific-behavior).
+/// that the last modified time of any file written **after** this method completes should be different.
-///
-/// Calling the function is only necessary when making changes to an **existing** file.
 fn next_io_tick() {
-    std::thread::sleep(Duration::from_nanos(200));
+    let temp = tempfile::tempfile().unwrap();
+
+    let last_modified = FileTime::from_last_modification_time(&temp.metadata().unwrap());
+
+    loop {
+        filetime::set_file_handle_times(&temp, None, Some(FileTime::now())).unwrap();
+
+        let new_last_modified = FileTime::from_last_modification_time(&temp.metadata().unwrap());
+
+        if new_last_modified != last_modified {
+            break;
+        }
+
+        std::thread::sleep(Duration::from_nanos(100));
+    }
 }
 
 #[test]