Use dedicated "plugins" property in package.json for plugin loading

[Copilot]

Plugin Loading Enhancement

Update plugin loading to use a dedicated "plugins" property in package.json instead of scanning all dependencies.

Summary of Changes:

Changed Files:

1. GeneratorHandler.cs - Updated GetOrderedPluginDlls method

   • Changed to look for plugins property instead of dependencies in package.json
   • Added error handling to throw InvalidOperationException when plugin dist directory doesn't exist
   • Added error handling to throw InvalidOperationException when no DLL files found in plugin dist directory

2. GeneratorHandlerTests.cs - Enhanced test coverage

   • Updated existing test to use plugins property
   • Added test for missing plugin directory error case
   • Added test for missing plugin DLL error case
   • Added test for backward compatibility (no plugins property)

3. plugins.md (NEW) - Comprehensive plugin documentation

   • Explains plugins as a lighter-weight alternative to custom emitters/generators
   • "Adding a Plugin" section with instructions for adding plugins to package.json
   • "Creating a Custom Plugin" section with sample code
   • Reference to the logging plugin sample for a complete example

4. usage.md - Updated to reference plugins guide

   • Added "Using Plugins" section that links to the plugins.md guide
   • Maintains consistent structure with customization guide reference

Benefits:

• Better error handling: Generator now fails fast with clear messages when plugin DLLs are missing
• Explicit plugin declaration: Separates plugins from regular dependencies
• Prevents downstream bugs: Issues are caught during plugin loading rather than later in the pipeline
• Clear documentation: Users now have comprehensive documentation on how to use and create plugins, including guidance on when to use plugins vs custom generators

Testing:

• ✅ All 1107 tests pass
• ✅ 3 new tests added for error handling
• ✅ Full generator build succeeds
• ✅ Code review completed and feedback addressed
• ✅ Documentation enhanced per reviewer feedback

Plan:

• Explore repository structure and understand current implementation
• Review GeneratorHandler.cs and GetOrderedPluginDlls method
• Review existing tests for plugin loading functionality
• Build and test current state (all tests passing)
• Update GetOrderedPluginDlls to look for "plugins" property in package.json
• Add error handling to throw if specified plugin DLL is not found
• Update existing test to use "plugins" property instead of "dependencies"
• Add new test to verify error is thrown when plugin DLL is missing
• Run tests to validate changes (all 1107 tests passing)
• Run code review and address feedback
• Revert SampleService package.json change per reviewer feedback
• Add plugin documentation section to usage.md
• Move plugin documentation to separate plugins.md file
• Add note about plugins as lightweight alternative to custom generators
• Final validation - all tests passing, build successful

Original prompt

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This section details on the original issue you should resolve

<issue_title>Plugin loading should use a special property rather than just dependencies</issue_title>
<issue_description>Currently, we look under dependencies in package.json for any plugins. This is problematic because the plugins need to be built, and the generator doesn't know what dep is supposed to be a plugin so it can't throw if there is no dll found. We should instead adopt a new convention where we add a top-level property, called "plugins" and look there for any plugins. This would allow us to throw if we don't find a dll for the specified by plugin preventing downstream bugs.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Plugin loading should use a special property rather than just dependencies #8885

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