[BUG] Diff view does not auto-scroll to bottom when streaming long content

[village-way]

Problem (one or two sentences)

When streaming long content into the diff view, the editor does not automatically scroll to follow the bottom of the content being written, making it difficult to see the latest changes in real-time.

Context (who is affected and when)

This affects all users when using Roo Code's diff view feature to review AI-generated code changes. The issue is most noticeable when:

• The AI generates or streams a large amount of content (hundreds or thousands of lines)
• Users want to see the latest changes as they are being written
• The content extends beyond the visible viewport

Reproduction steps

1. Open Roo Code extension in VS Code
2. Start a task that generates a large code diff (e.g., generate a new file with many lines or modify an existing file with extensive changes)
3. Observe the diff view as content is being streamed
4. Notice that the view does not automatically scroll to show the latest content at the bottom

Expected result

The diff view should automatically scroll to the bottom (or near the bottom) as new content is being streamed, allowing users to see the latest changes in real-time without manual scrolling.

Actual result

The diff view remains static at the top or middle of the document, requiring users to manually scroll down to see the latest content being written.

Variations tried (optional)

No response

App Version

3.36.7

API Provider (optional)

Anthropic

Model Used (optional)

No response

Roo Code Task Links (optional)

No response

Relevant logs or errors (optional)

I have analyzed this issue and identified the problem.

Root Cause:
In src/integrations/editor/DiffViewProvider.ts, the update() method (lines 152-156) has inverted scroll logic:

const ranges = this.activeDiffEditor?.visibleRanges
if (ranges && ranges.length > 0 && ranges[0].start.line < endLine && ranges[0].end.line > endLine) {
    this.scrollEditorToLine(endLine)
}

The condition ranges[0].end.line > endLine only triggers scrolling when endLine is within the visible range. For auto-scroll to follow streaming content at the bottom, it should scroll when endLine is beyond the visible range.

Proposed Implementation Plan:

1. Fix the scroll condition in the update() method to scroll when endLine exceeds or is near the visible range boundary
2. Change the condition from ranges[0].end.line > endLine to ranges[0].end.line <= endLine + 1 (scroll when the streamed line is at or beyond the visible range end)
3. Add tests to verify the auto-scroll behavior

Code Change:

// Scroll to the current line without stealing focus.
const ranges = this.activeDiffEditor?.visibleRanges
if (ranges && ranges.length > 0 && ranges[0].end.line <= endLine + 1) {
    this.scrollEditorToLine(endLine)
}

This approach:

• Scrolls automatically when new content extends beyond the visible viewport
• Uses endLine + 1 to provide a small buffer so scrolling happens just before the line goes out of view
• Maintains the existing scrollEditorToLine() logic that adds 4 lines offset and uses InCenter reveal type

Please mention @roomote in a comment saying that you approve this plan, and I will proceed with the implementation.