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>

3 files changed, 41 insertions, 3 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);
     }