Description

Bug Report: Edit Tool Corrupts Python Indentation (v1.14.39)

Description

The edit tool systematically corrupts Python file indentation when editing code inside indented blocks (try/except, functions, classes). The tool reports success but the file on disk has incorrect indentation, breaking Python syntax.

This is a critical data loss bug - the diff shows correct output but the actual file is corrupted.

Reproduction Steps

1. Create a Python file with indented code inside a try block:

def example():
    try:
        # Some code here
        result = process_data()
        return result
    except Exception as e:
        log_error(e)

2. Use the edit tool to modify the indented code:

oldString: "        result = process_data()\n        return result"
newString: "        result = process_data()\n        validate(result)\n        return result"

3. Tool reports "Edit applied successfully"

4. Actual result on disk:

def example():
    try:
result = process_data()
validate(result)
        return result
    except Exception as e:
        log_error(e)

5. Python raises IndentationError: expected an indented block

Root Cause Analysis

After running 200 systematic tests (100 edit + 100 write), I've identified:

What Works (100% success rate):

• ✅ Editing text that appears exactly once in the file
• ✅ Changes to constants, imports, comments (unique patterns)
• ✅ Using write tool for complete file rewrites

What Fails (100% failure rate):

• ❌ Editing code inside try/except blocks (19 occurrences of try: in test file)
• ❌ Editing code with generic patterns (if, except, try)
• ❌ Moving code between indentation levels
• ❌ Multiple consecutive edits without syntax validation

Test Data:

Environment

• OpenCode Desktop: v1.14.39
• LLM: Qwen3.5-397B-A17B
• OS: Windows 10 Pro for Workstations 22H2
• Build: 19045.7184
• Python: 3.x (any version affected)

Impact

• Cannot safely edit Python code inside any indented block
• Silent corruption - diff shows correct, file is broken
• No rollback - git sees the corrupted version as current
• Affects all Python developers using OpenCode

Related Issues

This bug persists despite being reported multiple times:

• Edit tool strips all leading whitespace from matched lines (space-indented Python files) #24549 (closed - but still occurs in v1.14.39)
• Edit tool messes with indentation (but this is not shown in the diff) #14612 (indentation changes not shown in diff)
• Edit Tool Not Applying Whitespace-Only Changes #20876 (whitespace-only changes ignored)
• There is a very high probability of encountering indentation bugs when using the Edit tool in OpenCode. #10656 (high probability of indentation bugs)

Evidence Files

Full investigation data available at:

• Test framework: test_indentation_lab/ (200 tests)
• Detailed analysis: [link to gist/repo]
• Exact failure cases: [link to specific test results]

Suggested Fixes

Immediate (User-side):

1. Pre-flight check: Count pattern occurrences before edit
2. Post-flight validation: Run py_compile after every edit
3. Auto-revert: If syntax validation fails, rollback automatically
4. Warning system: Alert if pattern appears multiple times

Long-term (Tool-side):

1. Diff-based editing: Use actual line numbers instead of text matching
2. Context intelligence: Include 3 lines of context before/after pattern
3. Indentation preservation: Never strip leading whitespace from matched lines
4. Validation pipeline: Integrate Python syntax checker into edit tool

Workaround (Current)

Until fixed, use this workflow:

1. For simple changes (unique text): edit tool is safe
2. For complex changes (indented blocks): Use write tool with full file content
3. Always validate: Run python -m py_compile file.py after every edit
4. Backup first: git stash or copy file before editing

Request

1. Reopen investigation into Edit tool strips all leading whitespace from matched lines (space-indented Python files) #24549 (bug still active)
2. Prioritize fix - this blocks all Python development with OpenCode
3. Add validation - at minimum, run syntax check after edit
4. Improve documentation - warn users about edit tool limitations

Severity: Critical (data loss, blocks core functionality)
Frequency: 100% on affected patterns
Workaround: Use write tool instead (cumbersome but safe)

Plugins

No response

OpenCode version

No response

Steps to reproduce

No response

Screenshot and/or share link

No response

Operating System

No response

Terminal

No response