[red-knot] Use web-time instead of FileTime::now (#16967)

## Summary

`std::time::now` isn't available on `wasm32-unknown-unknown` but it is
used by `FileTime::now`.

This PR replaces the usages of `FileTime::now` with a target specific
helper function that we already had in the memory file system.
Fixes https://github.com/astral-sh/ruff/issues/16966

## Test Plan

Tested that the playground no longer crash when adding an extra-path

crates/red_knot/tests/file_watching.rs

@@ -12,7 +12,7 @@ use red_knot_python_semantic::{resolve_module, ModuleName, PythonPlatform};
 use ruff_db::files::{system_path_to_file, File, FileError};
 use ruff_db::source::source_text;
 use ruff_db::system::{
-    OsSystem, System, SystemPath, SystemPathBuf, UserConfigDirectoryOverrideGuard,
+    file_time_now, OsSystem, System, SystemPath, SystemPathBuf, UserConfigDirectoryOverrideGuard,
 };
 use ruff_db::{Db as _, Upcast};
 use ruff_python_ast::PythonVersion;
@@ -462,7 +462,7 @@ fn update_file(path: impl AsRef<SystemPath>, content: &str) -> anyhow::Result<()
 
         std::thread::sleep(Duration::from_nanos(10));
 
-        filetime::set_file_handle_times(&file, None, Some(filetime::FileTime::now()))?;
+        filetime::set_file_handle_times(&file, None, Some(file_time_now()))?;
     }
 }
 

crates/ruff_db/src/file_revision.rs

@@ -1,3 +1,5 @@
+use crate::system::file_time_now;
+
 /// A number representing the revision of a file.
 ///
 /// Two revisions that don't compare equal signify that the file has been modified.
@@ -16,7 +18,7 @@ impl FileRevision {
     }
 
     pub fn now() -> Self {
-        Self::from(filetime::FileTime::now())
+        Self::from(file_time_now())
     }
 
     pub const fn zero() -> Self {
@@ -53,13 +55,12 @@ impl From<filetime::FileTime> for FileRevision {
 
 #[cfg(test)]
 mod tests {
-    use filetime::FileTime;
 
     use super::*;
 
     #[test]
     fn revision_from_file_time() {
-        let file_time = FileTime::now();
+        let file_time = file_time_now();
         let revision = FileRevision::from(file_time);
 
         let revision = revision.as_u128();

crates/ruff_db/src/system.rs

@@ -7,6 +7,7 @@ pub use os::testing::UserConfigDirectoryOverrideGuard;
 #[cfg(feature = "os")]
 pub use os::OsSystem;
 
+use filetime::FileTime;
 use ruff_notebook::{Notebook, NotebookError};
 use std::error::Error;
 use std::fmt::{Debug, Formatter};
@@ -346,3 +347,27 @@ pub enum GlobErrorKind {
     IOError(io::Error),
     NonUtf8Path,
 }
+
+#[cfg(not(target_arch = "wasm32"))]
+pub fn file_time_now() -> FileTime {
+    FileTime::now()
+}
+
+#[cfg(target_arch = "wasm32")]
+pub fn file_time_now() -> FileTime {
+    // Copied from FileTime::from_system_time()
+    let time = web_time::SystemTime::now();
+
+    time.duration_since(web_time::UNIX_EPOCH)
+        .map(|d| FileTime::from_unix_time(d.as_secs() as i64, d.subsec_nanos()))
+        .unwrap_or_else(|e| {
+            let until_epoch = e.duration();
+            let (sec_offset, nanos) = if until_epoch.subsec_nanos() == 0 {
+                (0, 0)
+            } else {
+                (-1, 1_000_000_000 - until_epoch.subsec_nanos())
+            };
+
+            FileTime::from_unix_time(-(until_epoch.as_secs() as i64) + sec_offset, nanos)
+        })
+}

crates/ruff_db/src/system/memory_fs.rs

@@ -7,8 +7,8 @@ use filetime::FileTime;
 use rustc_hash::FxHashMap;
 
 use crate::system::{
-    walk_directory, DirectoryEntry, FileType, GlobError, GlobErrorKind, Metadata, Result,
+    file_time_now, walk_directory, DirectoryEntry, FileType, GlobError, GlobErrorKind, Metadata,
-    SystemPath, SystemPathBuf, SystemVirtualPath, SystemVirtualPathBuf,
+    Result, SystemPath, SystemPathBuf, SystemVirtualPath, SystemVirtualPathBuf,
 };
 
 use super::walk_directory::{
@@ -163,7 +163,7 @@ impl MemoryFileSystem {
 
         let file = get_or_create_file(&mut by_path, &normalized)?;
         file.content = content.to_string();
-        file.last_modified = now();
+        file.last_modified = file_time_now();
 
         Ok(())
     }
@@ -215,7 +215,7 @@ impl MemoryFileSystem {
             std::collections::hash_map::Entry::Vacant(entry) => {
                 entry.insert(File {
                     content: content.to_string(),
-                    last_modified: now(),
+                    last_modified: file_time_now(),
                 });
             }
             std::collections::hash_map::Entry::Occupied(mut entry) => {
@@ -310,7 +310,7 @@ impl MemoryFileSystem {
         let mut by_path = self.inner.by_path.write().unwrap();
         let normalized = self.normalize_path(path.as_ref());
 
-        get_or_create_file(&mut by_path, &normalized)?.last_modified = now();
+        get_or_create_file(&mut by_path, &normalized)?.last_modified = file_time_now();
 
         Ok(())
     }
@@ -486,7 +486,7 @@ fn create_dir_all(
         path.push(component);
         let entry = paths.entry(path.clone()).or_insert_with(|| {
             Entry::Directory(Directory {
-                last_modified: now(),
+                last_modified: file_time_now(),
             })
         });
 
@@ -513,7 +513,7 @@ fn get_or_create_file<'a>(
     let entry = paths.entry(normalized.to_path_buf()).or_insert_with(|| {
         Entry::File(File {
             content: String::new(),
-            last_modified: now(),
+            last_modified: file_time_now(),
         })
     });
 
@@ -695,30 +695,6 @@ enum WalkerState {
     Nested { path: SystemPathBuf, depth: usize },
 }
 
-#[cfg(not(target_arch = "wasm32"))]
-fn now() -> FileTime {
-    FileTime::now()
-}
-
-#[cfg(target_arch = "wasm32")]
-fn now() -> FileTime {
-    // Copied from FileTime::from_system_time()
-    let time = web_time::SystemTime::now();
-
-    time.duration_since(web_time::UNIX_EPOCH)
-        .map(|d| FileTime::from_unix_time(d.as_secs() as i64, d.subsec_nanos()))
-        .unwrap_or_else(|e| {
-            let until_epoch = e.duration();
-            let (sec_offset, nanos) = if until_epoch.subsec_nanos() == 0 {
-                (0, 0)
-            } else {
-                (-1, 1_000_000_000 - until_epoch.subsec_nanos())
-            };
-
-            FileTime::from_unix_time(-(until_epoch.as_secs() as i64) + sec_offset, nanos)
-        })
-}
-
 #[cfg(test)]
 mod tests {
     use std::io::ErrorKind;