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PLUGIN_RELOAD_DIFF_IMPLEMENTATION.md

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Plugin Hot-Reload Diff Implementation

Summary

Implemented a feature to show clear diffs when plugins are hot-reloaded, making it easier for developers to verify reload results during iterative plugin development.

Changes Made

1. Core Implementation (src/plugin/registry.rs)

New Structures

  • PluginSnapshot: Captures plugin state at a point in time

    • Name, version, capabilities, commands, formatters, dependencies

  • PluginReloadDiff: Represents changes detected during reload

    • Version changes (old → new)
    • Capability changes (enabled/disabled)
    • Commands added/removed
    • Formatters added/removed
    • Dependencies added/removed

Modified Functions

  • reload_plugin(): Now returns PluginResult<PluginReloadDiff> instead of PluginResult<()>
    • Captures plugin state before reload
    • Captures plugin state after reload
    • Computes diff between states
    • Emits concise summary to logs

Key Features

  • Automatic change detection: Tracks all plugin metadata changes
  • Sorted output: All lists (commands, formatters, dependencies) are sorted for consistent output
  • Concise summaries: Human-readable format showing only what changed
  • No changes detection: Special message when plugin reloads with no changes

2. Module Exports (src/plugin/mod.rs)

  • Exported PluginReloadDiff type for use by other modules

3. Documentation Updates

src/plugin/README.md

Added section on "Hot-Reload with Change Detection" explaining:

  • What changes are detected
  • Example reload output
  • Benefits for iterative development

docs/plugin-api.md

Enhanced "Hot-Reload Support" section with:

  • Detailed explanation of change detection
  • Example outputs for various scenarios
  • Benefits for plugin developers

4. Comprehensive Tests (src/plugin/registry.rs)

Added 8 new test cases:

  • reload_diff_detects_version_change
  • reload_diff_detects_capability_changes
  • reload_diff_detects_added_and_removed_commands
  • reload_diff_detects_added_and_removed_formatters
  • reload_diff_detects_dependency_changes
  • reload_diff_reports_no_changes_when_identical
  • reload_diff_summary_is_concise_and_readable

Example Output

With Changes

Plugin 'example-logger' reload changes:
  Version: 1.0.0 → 1.1.0
  Capabilities:
    provides_commands: false → true
  Commands added: log-stats, clear-log
  Formatters added: json-formatter
  Dependencies added: helper-plugin

No Changes

Plugin 'example-logger' reloaded with no changes

Acceptance Criteria Met

✅ Plugin reloads emit a concise diff of added, removed, and changed capabilities
✅ Developers can verify the reload result immediately
✅ Tests are added for the changed behavior
✅ User-facing docs are updated

Files Modified

  1. src/plugin/registry.rs - Core implementation
  2. src/plugin/mod.rs - Module exports
  3. src/plugin/README.md - User documentation
  4. docs/plugin-api.md - API documentation

Technical Details

Diff Computation Algorithm

  1. Compare versions (string equality)
  2. Compare each capability field (boolean equality)
  3. Convert command/formatter/dependency lists to HashSets
  4. Compute set differences for added/removed items
  5. Sort all result lists for consistent output

Display Format

  • Uses Display trait implementation for easy printing
  • Hierarchical indentation for readability
  • Only shows sections with changes
  • Special handling for "no changes" case

Benefits

  1. Immediate feedback: Developers know instantly what changed
  2. Trust: Clear verification that changes were loaded correctly
  3. Debugging: Easier to spot unintended changes or regressions
  4. Documentation: Reload output serves as a change log

Future Enhancements

Potential improvements for future iterations:

  • Colorized output for better visual distinction
  • Detailed command/formatter signature changes
  • Performance metrics (reload time)
  • Rollback capability on failed reloads