jumperless-boardboard-v5/RP23V50firmware/CodeDocs/REPL_Multiline_Editing_Improvements.md

REPL Multiline Editing Improvements

Overview

Completely revamped multiline editing in the Jumperless MicroPython REPL using a full buffer synchronization approach. This eliminates all display inconsistencies and ensures perfect synchronization between the internal buffer and what's displayed on screen.

Problems Fixed

1. Line Content Disappearing During Edit

• Issue: When editing a line in multiline mode, the line would clear but not show the updated content properly
• Cause: Partial screen updates getting out of sync with terminal state
• Solution: Complete buffer redraw on every keystroke ensures perfect synchronization

2. Inconsistent Display Updates

• Issue: What was typed would be executed correctly but not always displayed on screen
• Cause: Race conditions between incremental display updates and terminal control sequences
• Solution: Full buffer approach eliminates race conditions by always showing the complete current state

3. Cursor Positioning Issues

• Issue: Cursor would end up in wrong position after editing multiline content
• Cause: Accumulating errors from incremental cursor movement commands
• Solution: Precise cursor positioning calculation based on actual buffer content and cursor position

Technical Changes

New Full Buffer Approach

Core Philosophy

• Complete Redraw: Every keystroke triggers a full redraw of the entire input buffer
• Buffer Synchronization: Internal buffer state is always perfectly reflected on screen
• Precise Positioning: Cursor position calculated based on actual buffer content, not incremental movements
• Accurate Line Tracking: Fixed line clearing logic to prevent screen scrolling issues

Modified Functions in src/Python_Proper.cpp

redrawFullInput() (Enhanced)

• Now used for ALL display updates, not just specific cases
• Added positionCursorAtCurrentPos() for precise cursor positioning
• Completely clears display area and redraws entire buffer with proper prompts
• Handles multiline syntax highlighting correctly

positionCursorAtCurrentPos() (New)

• Calculates exact line and column position based on cursor_pos in buffer
• Accounts for prompt lengths (">>>" vs "...")
• Moves cursor to precise location using terminal control sequences
• Handles multiline navigation correctly

Input Handling Logic (Completely Revised)

• All Operations: Character input, backspace, tab, arrow keys ALL use full redraw
• Eliminated Incremental Updates: No more partial screen updates or character echoing
• Perfect Consistency: What you see is exactly what's in the buffer, always

Line Clearing Fix (Critical Bug Fix)

• Issue: Going up a line was erasing one extra line, causing screen scrolling
• Root Cause: last_displayed_lines was tracking newline count instead of actual cursor movement needed
• Solution: Now tracks lines_printed which represents lines moved down from first line
• Result: Perfect line clearing without unwanted screen scrolling

Testing

Basic Testing

1. Enter multiline mode by typing code that requires multiple lines:

def test_function():
    print("line 1")
    print("line 2")
    return "done"

2. Use arrow keys to navigate to the middle of any line
3. Edit the content (add/remove characters)
4. Verify the line displays correctly and stays visible

Advanced Testing

Use the comprehensive test scripts:

# Basic functionality test
exec(open('/path/to/test_multiline_editing.py').read())

# Full buffer synchronization test
exec(open('/path/to/test_full_buffer_multiline.py').read())

# Line clearing fix verification test
exec(open('/path/to/test_line_clearing_fix.py').read())

Expected Behavior

• ✅ Perfect Synchronization: Buffer content always matches display exactly
• ✅ Reliable Cursor Position: Cursor always positioned correctly, never out of sync
• ✅ Complete Redraw: Every keystroke shows immediate, complete result
• ✅ Multiline Navigation: Arrow keys work perfectly in complex multiline structures
• ✅ No Display Artifacts: No leftover characters or partial line updates
• ✅ Syntax Highlighting: Works correctly across all multiline content
• ✅ Edit Anywhere: Can edit any character in any line without display issues

Memory Usage

The full buffer approach uses slightly more resources but ensures reliability:

• Complete buffer redraw on each keystroke (acceptable performance impact)
• Enhanced cursor position calculation
• Eliminated incremental update complexity
• Overall more reliable and maintainable code

Backward Compatibility

All changes are fully backward compatible:

• Existing REPL functionality unchanged
• All keyboard shortcuts and commands work as before
• History navigation still works perfectly
• File operations and special commands unchanged

Performance Impact

• Multiline editing: Small increase in redraw time, but perfect reliability
• Single-line editing: Same full redraw approach, consistent experience
• Terminal responsiveness: Improved due to elimination of synchronization issues
• Visual feedback: Immediate and always accurate display updates

Future Improvements

• Optional performance optimization: Only redraw when buffer actually changes
• Add configurable redraw modes (full vs. smart) for different terminal capabilities
• Implement line wrapping for extremely long lines (>terminal width)
• Add visual indicators for multiline mode status
• Consider terminal size detection for adaptive display

Technical Architecture

Buffer Management

• Single Source of Truth: current_input string contains entire buffer
• Cursor Tracking: cursor_pos integer tracks character position in buffer
• Display Synchronization: redrawFullInput() ensures screen matches buffer exactly

Terminal Control Flow

1. Input Received → Update buffer (current_input) and cursor position (cursor_pos)
2. Full Redraw → Clear display area, redraw entire buffer with syntax highlighting
3. Cursor Positioning → Calculate exact screen position and move cursor there
4. Flush → Ensure all terminal commands are processed

Key Benefits

• Eliminates State Drift: No accumulation of display/buffer mismatches
• Predictable Behavior: Every keystroke produces same result regardless of history
• Easier Debugging: Single redraw function handles all display logic
• Robust Navigation: Arrow keys work correctly in any multiline scenario

Related Files

• src/Python_Proper.cpp - Main REPL implementation with full buffer logic
• src/Python_Proper.h - REPL editor structure definitions
• CodeDocs/examples/test_multiline_editing.py - Basic functionality testing
• CodeDocs/examples/test_full_buffer_multiline.py - Comprehensive buffer sync testing
• CodeDocs/examples/test_line_clearing_fix.py - Line clearing fix verification

Memory References

• memory:2792014 - C++ serial output requires \r\n for proper cursor positioning
• memory:240128 - MicroPython REPL with proper multiline state tracking
• memory:240161 - Complete REPL implementation with edge case handling