Protect against overwriting external changes

When saving, check that the file has not changed before our last known
save before writing the file. Only overwrite external changes if asked
to force.

helix-term/tests/test/commands.rs

@@ -67,7 +67,7 @@ async fn test_buffer_close_concurrent() -> anyhow::Result<()> {
     const RANGE: RangeInclusive<i32> = 1..=1000;
 
     for i in RANGE {
-        let cmd = format!("%c{}<esc>:w<ret>", i);
+        let cmd = format!("%c{}<esc>:w!<ret>", i);
         command.push_str(&cmd);
     }
 

helix-term/tests/test/helpers.rs

@@ -322,6 +322,12 @@ impl AppBuilder {
     }
 }
 
+pub async fn run_event_loop_to_idle(app: &mut Application) {
+    let (_, rx) = tokio::sync::mpsc::unbounded_channel();
+    let mut rx_stream = UnboundedReceiverStream::new(rx);
+    app.event_loop_until_idle(&mut rx_stream).await;
+}
+
 pub fn assert_file_has_content(file: &mut File, content: &str) -> anyhow::Result<()> {
     file.flush()?;
     file.sync_all()?;

helix-term/tests/test/write.rs

@@ -1,5 +1,5 @@
 use std::{
-    io::{Read, Write},
+    io::{Read, Seek, SeekFrom, Write},
     ops::RangeInclusive,
 };
 
@@ -37,6 +37,38 @@ async fn test_write() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread")]
+async fn test_overwrite_protection() -> anyhow::Result<()> {
+    let mut file = tempfile::NamedTempFile::new()?;
+    let mut app = helpers::AppBuilder::new()
+        .with_file(file.path(), None)
+        .build()?;
+
+    helpers::run_event_loop_to_idle(&mut app).await;
+
+    file.as_file_mut()
+        .write_all(helpers::platform_line("extremely important content").as_bytes())?;
+
+    file.as_file_mut().flush()?;
+    file.as_file_mut().sync_all()?;
+
+    test_key_sequence(&mut app, Some(":x<ret>"), None, false).await?;
+
+    file.as_file_mut().flush()?;
+    file.as_file_mut().sync_all()?;
+
+    file.seek(SeekFrom::Start(0))?;
+    let mut file_content = String::new();
+    file.as_file_mut().read_to_string(&mut file_content)?;
+
+    assert_eq!(
+        helpers::platform_line("extremely important content"),
+        file_content
+    );
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread")]
 async fn test_write_quit() -> anyhow::Result<()> {
     let mut file = tempfile::NamedTempFile::new()?;
@@ -76,7 +108,7 @@ async fn test_write_concurrent() -> anyhow::Result<()> {
         .build()?;
 
     for i in RANGE {
-        let cmd = format!("%c{}<esc>:w<ret>", i);
+        let cmd = format!("%c{}<esc>:w!<ret>", i);
         command.push_str(&cmd);
     }
 

helix-view/src/document.rs

@@ -13,6 +13,7 @@ use std::future::Future;
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
 use std::sync::Arc;
+use std::time::SystemTime;
 
 use helix_core::{
     encoding,
@@ -127,6 +128,10 @@ pub struct Document {
 
     pub savepoint: Option<Transaction>,
 
+    // Last time we wrote to the file. This will carry the time the file was last opened if there
+    // were no saves.
+    last_saved_time: SystemTime,
+
     last_saved_revision: usize,
     version: i32, // should be usize?
     pub(crate) modified_since_accessed: bool,
@@ -368,6 +373,7 @@ impl Document {
             version: 0,
             history: Cell::new(History::default()),
             savepoint: None,
+            last_saved_time: SystemTime::now(),
             last_saved_revision: 0,
             modified_since_accessed: false,
             language_server: None,
@@ -557,9 +563,11 @@ impl Document {
 
         let encoding = self.encoding;
 
+        let last_saved_time = self.last_saved_time;
+
         // We encode the file according to the `Document`'s encoding.
         let future = async move {
-            use tokio::fs::File;
+            use tokio::{fs, fs::File};
             if let Some(parent) = path.parent() {
                 // TODO: display a prompt asking the user if the directories should be created
                 if !parent.exists() {
@@ -571,6 +579,17 @@ impl Document {
                 }
             }
 
+            // Protect against overwriting changes made externally
+            if !force {
+                if let Ok(metadata) = fs::metadata(&path).await {
+                    if let Ok(mtime) = metadata.modified() {
+                        if last_saved_time < mtime {
+                            bail!("file modified by an external process, use :w! to force");
+                        }
+                    }
+                }
+            }
+
             let mut file = File::create(&path).await?;
             to_writer(&mut file, encoding, &text).await?;
 
@@ -644,6 +663,8 @@ impl Document {
         self.append_changes_to_history(view.id);
         self.reset_modified();
 
+        self.last_saved_time = SystemTime::now();
+
         self.detect_indent_and_line_ending();
 
         Ok(())
@@ -979,6 +1000,7 @@ impl Document {
             rev
         );
         self.last_saved_revision = rev;
+        self.last_saved_time = SystemTime::now();
     }
 
     /// Get the document's latest saved revision.