fix: preserve viewport position when applying diffs to active editor

[heyseth]

Related GitHub Issue

Closes: #8112

Description

This PR fixes the viewport jumping issue when Roo edits a file that's currently open. Previously, the editor would reset to the top of the file or scroll to the edited lines, breaking the user's workflow. Now the exact scroll position is preserved throughout the edit process.

Implementation approach:

• Viewport capture timing: The viewport position (visibleRanges and viewColumn) is captured in the open() method before the original file tab is closed and the diff view is opened. This ensures we have the true pre-edit viewport state.
• Storage: Two new private properties store the captured state:
  • originalViewportRanges: The visible line ranges in the editor
  • originalViewColumn: Which column/pane the editor was in
• Restoration strategy: The viewport is restored by revealing the middle line of the original visible range using TextEditorRevealType.InCenter.
• Coverage: The fix applies to three code paths:
  • saveChanges(): Normal diff view workflow
  • revertChanges(): When user rejects changes
  • saveDirectly(): PREVENT_FOCUS_DISRUPTION experiment path (no diff view)

Test Procedure

1. Autosave changes viewport test:

   • Open a large file (500+ lines) in VSCode
   • Scroll to line 300
   • Ensure that write permissions are enabled for Roo
   • Use Roo to edit the file (e.g., "add a comment at line 50")
   • Expected: Editor remains scrolled to line 300
   • Result: ✅ Viewport preserved correctly

2. Manual save changes viewport test:

   • Open a file scrolled to middle
   • Ensure that write permissions are disabled for Roo
   • Use Roo to edit the file
   • Manually accept the changes
   • Expected: File saves and viewport preserved
   • Result: ✅ Viewport preserved correctly

3. Manual revert changes viewport test:

   • Open a file scrolled to middle
   • Ensure that write permissions are disabled for Roo
   • Use Roo to edit the file
   • Manually reject the changes
   • Expected: File reverts and viewport preserved
   • Result: ✅ Viewport preserved on revert

4. New file creation viewport test:

   • Use Roo to create a new file
   • Expected: File opens normally (no viewport restoration)
   • Result: ✅ Works correctly

5. PREVENT_FOCUS_DISRUPTION experiment:

   • Enable the "background editing" experimental flag
   • Open file scrolled to middle
   • Use Roo to apply a diff (uses saveDirectly() path)
   • Expected: Viewport preserved without diff view
   • Result: ✅ Viewport preserved

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: New and/or updated tests have been added to cover my changes (if applicable).
• Documentation Impact: I have considered if my changes require documentation updates (see "Documentation Updates" section below).
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Documentation Updates

• No documentation updates are required.

Additional Notes

Get in Touch

Discord: @ocean.smith

---

Important

Preserve editor viewport position when applying diffs in DiffViewProvider by capturing and restoring viewport state.

• Behavior:
  • Preserve viewport position in DiffViewProvider when applying diffs to active editor.
  • Capture visibleRanges and viewColumn in open() before closing original tab.
  • Restore viewport using TextEditorRevealType.InCenter in saveChanges(), revertChanges(), and saveDirectly().
• Implementation:
  • Add originalViewportRanges and originalViewColumn properties to store viewport state.
  • Modify open(), saveChanges(), revertChanges(), and saveDirectly() to handle viewport restoration.
• Misc:
  • Ensure viewport restoration applies to normal, revert, and experimental save paths.

^{This description was created by for fac6fba. You can customize this summary. It will automatically update as commits are pushed.}