fix: track contents to avoid reloading on our own writes (#7099)

This PR track contents that we wrong to avoid reloading on our own
writes when file watching.

Author: mscolnick

marimo/_server/file_manager.py

@@ -47,6 +47,8 @@ def __init__(
         )
         self._default_sql_output: SqlOutputType | None = default_sql_output
         self.app = self._load_app(self.path)
+        # Track the last saved content to avoid reloading our own writes
+        self._last_saved_content: Optional[str] = None
 
     @staticmethod
     def from_app(app: InternalApp) -> AppFileManager:
@@ -128,6 +130,7 @@ def _rename_file(self, new_filename: str) -> None:
     def _save_file(
         self,
         filename: str,
+        *,
         notebook: NotebookSerializationV1,
         # Whether or not to persist the app to the file system
         persist: bool,
@@ -180,6 +183,8 @@ def _save_file(
 
         if persist:
             self._create_file(filename, contents)
+            # Record the last saved content to avoid reloading our own writes
+            self._last_saved_content = contents.strip()
 
         if self._is_unnamed():
             self.rename(filename)
@@ -241,7 +246,7 @@ def rename(self, new_filename: str) -> None:
         if needs_save:
             self._save_file(
                 self.filename,
-                self.app.to_ir(),
+                notebook=self.app.to_ir(),
                 persist=True,
                 previous_filename=previous_filename,
             )
@@ -286,7 +291,7 @@ def save_app_config(self, config: dict[str, Any]) -> str:
         if self.filename is not None:
             return self._save_file(
                 self.filename,
-                self.app.to_ir(),
+                notebook=self.app.to_ir(),
                 persist=True,
             )
         return ""
@@ -330,7 +335,7 @@ def save(self, request: SaveNotebookRequest) -> str:
             self.app.update_config({"layout_file": None})
         return self._save_file(
             filename,
-            self.app.to_ir(),
+            notebook=self.app.to_ir(),
             persist=request.persist,
         )
 
@@ -360,6 +365,26 @@ def read_file(self) -> str:
             )
         return Path(self.filename).read_text(encoding="utf-8")
 
+    def file_content_matches_last_save(self) -> bool:
+        """Check if the current file content matches the last saved content.
+
+        This is used to avoid reloading the file when we detect our own writes.
+
+        Returns:
+            bool: True if the file content matches the last save, False otherwise.
+        """
+        if self.filename is None or self._last_saved_content is None:
+            return False
+
+        try:
+            current_content = Path(self.filename).read_text(encoding="utf-8")
+            return current_content.strip() == self._last_saved_content
+        except Exception as e:
+            LOGGER.debug(
+                f"Error reading file to check if content matches: {e}"
+            )
+            return False
+
 
 def read_css_file(css_file: str, filename: Optional[str]) -> Optional[str]:
     """Read the contents of a CSS file.

marimo/_server/sessions.py

@@ -1186,6 +1186,14 @@ def _handle_file_change(
     ) -> None:
         LOGGER.debug(f"{file_path} was modified, handling {session}")
 
+        # Check if the file content matches the last save
+        # to avoid reloading our own writes
+        if session.app_file_manager.file_content_matches_last_save():
+            LOGGER.debug(
+                f"File {file_path} content matches last save, skipping reload"
+            )
+            return
+
         # Reload the file manager to get the latest code
         try:
             changed_cell_ids = session.app_file_manager.reload()

tests/_server/test_file_manager.py

@@ -793,3 +793,63 @@ def cell2():
     deleted_cell_ids = set(original_cell_ids) - set(reloaded_cell_ids)
     assert len(deleted_cell_ids) == 2
     assert deleted_cell_ids.issubset(changed_cell_ids)
+
+
+def test_file_content_matches_last_save(tmp_path: Path) -> None:
+    """Test that file_content_matches_last_save correctly identifies own writes."""
+    # Create a temporary file
+    temp_file = tmp_path / "test_match_save.py"
+    temp_file.write_text(
+        """
+import marimo
+app = marimo.App()
+
+@app.cell
+def cell1():
+    x = 1
+    return x
+
+if __name__ == "__main__":
+    app.run()
+"""
+    )
+
+    # Initialize AppFileManager
+    manager = AppFileManager(filename=str(temp_file))
+
+    # Initially, no save has been made by the manager
+    assert manager.file_content_matches_last_save() is False
+
+    # Save the file
+    manager.save(
+        SaveNotebookRequest(
+            cell_ids=[CellId_t("1")],
+            filename=str(temp_file),
+            codes=["x = 1"],
+            names=["cell1"],
+            configs=[CellConfig()],
+            persist=True,
+        )
+    )
+
+    # Now the file should match the last save
+    assert manager.file_content_matches_last_save() is True
+
+    # Externally modify the file
+    temp_file.write_text(
+        """
+import marimo
+app = marimo.App()
+
+@app.cell
+def cell1():
+    x = 2  # Changed
+    return x
+
+if __name__ == "__main__":
+    app.run()
+"""
+    )
+
+    # Now the file should not match the last save
+    assert manager.file_content_matches_last_save() is False