Add fs::MTime newtype and fix assumptions of temporal ordering

See ["mtime comparison considered
harmful"](https://apenwarr.ca/log/20181113) for details of why
comparators other than equality/inequality should not be used with
mtime.

crates/assistant/src/context_store.rs

@@ -770,7 +770,7 @@ impl ContextStore {
                         contexts.push(SavedContextMetadata {
                             title: title.to_string(),
                             path,
-                            mtime: metadata.mtime.into(),
+                            mtime: metadata.mtime.timestamp_for_user().into(),
                         });
                     }
                 }

crates/copilot/src/copilot.rs

@@ -1231,7 +1231,7 @@ mod tests {
 
         fn disk_state(&self) -> language::DiskState {
             language::DiskState::Present {
-                mtime: std::time::UNIX_EPOCH,
+                mtime: ::fs::MTime::from_seconds_and_nanos(100, 42),
             }
         }
 

crates/editor/Cargo.toml

@@ -42,6 +42,7 @@ emojis.workspace = true
 file_icons.workspace = true
 futures.workspace = true
 fuzzy.workspace = true
+fs.workspace = true
 git.workspace = true
 gpui.workspace = true
 http_client.workspace = true

crates/editor/src/items.rs

@@ -1620,13 +1620,11 @@ mod tests {
     use crate::editor_tests::init_test;
 
     use super::*;
+    use fs::MTime;
     use gpui::{AppContext, VisualTestContext};
     use language::{LanguageMatcher, TestFile};
     use project::FakeFs;
-    use std::{
-        path::{Path, PathBuf},
-        time::SystemTime,
-    };
+    use std::path::{Path, PathBuf};
 
     #[gpui::test]
     fn test_path_for_file(cx: &mut AppContext) {
@@ -1679,9 +1677,7 @@ mod tests {
     async fn test_deserialize(cx: &mut gpui::TestAppContext) {
         init_test(cx, |_| {});
 
-        let now = SystemTime::now();
         let fs = FakeFs::new(cx.executor());
-        fs.set_next_mtime(now);
         fs.insert_file("/file.rs", Default::default()).await;
 
         // Test case 1: Deserialize with path and contents
@@ -1695,7 +1691,7 @@ mod tests {
                 abs_path: Some(PathBuf::from("/file.rs")),
                 contents: Some("fn main() {}".to_string()),
                 language: Some("Rust".to_string()),
-                mtime: Some(now),
+                mtime: Some(fs.get_and_increment_mtime()),
             };
 
             DB.save_serialized_editor(item_id, workspace_id, serialized_editor.clone())
@@ -1792,9 +1788,7 @@ mod tests {
             let workspace_id = workspace::WORKSPACE_DB.next_id().await.unwrap();
 
             let item_id = 9345 as ItemId;
-            let old_mtime = now
-                .checked_sub(std::time::Duration::from_secs(60 * 60 * 24))
-                .unwrap();
+            let old_mtime = MTime::from_seconds_and_nanos(0, 50);
             let serialized_editor = SerializedEditor {
                 abs_path: Some(PathBuf::from("/file.rs")),
                 contents: Some("fn main() {}".to_string()),

crates/editor/src/persistence.rs

@@ -1,8 +1,8 @@
 use anyhow::Result;
 use db::sqlez::bindable::{Bind, Column, StaticColumnCount};
 use db::sqlez::statement::Statement;
+use fs::MTime;
 use std::path::PathBuf;
-use std::time::{Duration, SystemTime, UNIX_EPOCH};
 
 use db::sqlez_macros::sql;
 use db::{define_connection, query};
@@ -14,7 +14,7 @@ pub(crate) struct SerializedEditor {
     pub(crate) abs_path: Option<PathBuf>,
     pub(crate) contents: Option<String>,
     pub(crate) language: Option<String>,
-    pub(crate) mtime: Option<SystemTime>,
+    pub(crate) mtime: Option<MTime>,
 }
 
 impl StaticColumnCount for SerializedEditor {
@@ -29,16 +29,13 @@ impl Bind for SerializedEditor {
         let start_index = statement.bind(&self.contents, start_index)?;
         let start_index = statement.bind(&self.language, start_index)?;
 
-        let mtime = self.mtime.and_then(|mtime| {
-            mtime
-                .duration_since(UNIX_EPOCH)
-                .ok()
-                .map(|duration| (duration.as_secs() as i64, duration.subsec_nanos() as i32))
-        });
-        let start_index = match mtime {
+        let start_index = match self
+            .mtime
+            .and_then(|mtime| mtime.to_seconds_and_nanos_for_persistence())
+        {
             Some((seconds, nanos)) => {
-                let start_index = statement.bind(&seconds, start_index)?;
-                statement.bind(&nanos, start_index)?
+                let start_index = statement.bind(&(seconds as i64), start_index)?;
+                statement.bind(&(nanos as i32), start_index)?
             }
             None => {
                 let start_index = statement.bind::<Option<i64>>(&None, start_index)?;
@@ -64,7 +61,7 @@ impl Column for SerializedEditor {
 
         let mtime = mtime_seconds
             .zip(mtime_nanos)
-            .map(|(seconds, nanos)| UNIX_EPOCH + Duration::new(seconds as u64, nanos as u32));
+            .map(|(seconds, nanos)| MTime::from_seconds_and_nanos(seconds as u64, nanos as u32));
 
         let editor = Self {
             abs_path,
@@ -280,12 +277,11 @@ mod tests {
         assert_eq!(have, serialized_editor);
 
         // Storing and retrieving mtime
-        let now = SystemTime::now();
         let serialized_editor = SerializedEditor {
             abs_path: None,
             contents: None,
             language: None,
-            mtime: Some(now),
+            mtime: Some(MTime::from_seconds_and_nanos(100, 42)),
         };
 
         DB.save_serialized_editor(1234, workspace_id, serialized_editor.clone())

crates/extension_host/src/extension_host.rs

@@ -337,7 +337,7 @@ impl ExtensionStore {
                 if let (Ok(Some(index_metadata)), Ok(Some(extensions_metadata))) =
                     (index_metadata, extensions_metadata)
                 {
-                    if index_metadata.mtime > extensions_metadata.mtime {
+                    if index_metadata.mtime != extensions_metadata.mtime {
                         extension_index_needs_rebuild = false;
                     }
                 }

crates/fs/Cargo.toml

@@ -24,8 +24,10 @@ libc.workspace = true
 parking_lot.workspace = true
 paths.workspace = true
 rope.workspace = true
+rpc.workspace = true
 serde.workspace = true
 serde_json.workspace = true
+serde_derive.workspace = true
 smol.workspace = true
 tempfile.workspace = true
 text.workspace = true