Check for external file modifications when writing (#5805)

`:write` and other file-saving commands now check the file modification
time before writing to protect against overwriting external changes.

Co-authored-by: Gustavo Noronha Silva <gustavo@noronha.dev.br>
Co-authored-by: LeoniePhiline <22329650+LeoniePhiline@users.noreply.github.com>
Co-authored-by: Pascal Kuthe <pascal.kuthe@semimod.de>

4 files changed, 65 insertions, 4 deletions

diff --git a/helix-term/tests/test/commands.rs b/helix-term/tests/test/commands.rs
index da2e020e..2ca9e395 100644
--- a/helix-term/tests/test/commands.rs
+++ b/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);
     }
 
diff --git a/helix-term/tests/test/helpers.rs b/helix-term/tests/test/helpers.rs
index 8755b60f..fb12ef12 100644
--- a/helix-term/tests/test/helpers.rs
+++ b/helix-term/tests/test/helpers.rs
@@ -319,6 +319,12 @@ impl AppBuilder {
     }
 }
 
+pub async fn run_event_loop_until_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()?;
diff --git a/helix-term/tests/test/write.rs b/helix-term/tests/test/write.rs
index bbf14fc2..81459b2f 100644
--- a/helix-term/tests/test/write.rs
+++ b/helix-term/tests/test/write.rs
@@ -1,5 +1,5 @@
 use std::{
-    io::{Read, Write},
+    io::{Read, Seek, SeekFrom, Write},
     ops::RangeInclusive,
 };
 
@@ -38,6 +38,38 @@ async fn test_write() -> anyhow::Result<()> {
 }
 
 #[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_until_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()?;
     let mut app = helpers::AppBuilder::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);
     }
 
diff --git a/helix-view/src/document.rs b/helix-view/src/document.rs
index 798b5400..d308d013 100644
--- a/helix-view/src/document.rs
+++ b/helix-view/src/document.rs
@@ -19,6 +19,7 @@ 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,
@@ -135,6 +136,10 @@ 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,
@@ -160,6 +165,7 @@ impl fmt::Debug for Document {
             .field("changes", &self.changes)
             .field("old_state", &self.old_state)
             // .field("history", &self.history)
+            .field("last_saved_time", &self.last_saved_time)
             .field("last_saved_revision", &self.last_saved_revision)
             .field("version", &self.version)
             .field("modified_since_accessed", &self.modified_since_accessed)
@@ -382,6 +388,7 @@ 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,
@@ -577,9 +584,11 @@ 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() {
@@ -591,6 +600,17 @@ 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 overwrite");
+                        }
+                    }
+                }
+            }
+
             let mut file = File::create(&path).await?;
             to_writer(&mut file, encoding, &text).await?;
 
@@ -668,6 +688,8 @@ impl Document {
         self.append_changes_to_history(view);
         self.reset_modified();
 
+        self.last_saved_time = SystemTime::now();
+
         self.detect_indent_and_line_ending();
 
         match provider_registry.get_diff_base(&path) {
@@ -1016,6 +1038,7 @@ impl Document {
             rev
         );
         self.last_saved_revision = rev;
+        self.last_saved_time = SystemTime::now();
     }
 
     /// Get the document's latest saved revision.