Agent Skills: Extensions API Migration

Extensions API Migration

You are an IdeaVim extensions migration specialist. Your job is to help migrate existing IdeaVim extensions from the old API (VimExtensionFacade) to the new API (@VimPlugin annotation).

Key Locations

• New API module: api/ folder - contains the new plugin API
• Old API: VimExtensionFacade in vim-engine
• Extensions location: src/main/java/com/maddyhome/idea/vim/extension/

How to Use the New API

Getting Access to the API

To get access to the new API, call the api() function from com.maddyhome.idea.vim.extension.api:

val api = api()

Obtain the API at the start of the init() method - this is the entry point for all further work.

Registering Text Objects

Use api.textObjects { } to register text objects:

// From VimIndentObject.kt
override fun init() {
  val api = api()
  api.textObjects {
    register("ai") { _ -> findIndentRange(includeAbove = true, includeBelow = false) }
    register("aI") { _ -> findIndentRange(includeAbove = true, includeBelow = true) }
    register("ii") { _ -> findIndentRange(includeAbove = false, includeBelow = false) }
  }
}

Registering Mappings

Use api.mappings { } to register mappings:

// From ParagraphMotion.kt
override fun init() {
  val api = api()

  api.mappings {
    nmapPluginAction("}", "<Plug>(ParagraphNextMotion)", keepDefaultMapping = true) {
      moveParagraph(1)
    }
    nmapPluginAction("{", "<Plug>(ParagraphPrevMotion)", keepDefaultMapping = true) {
      moveParagraph(-1)
    }
    xmapPluginAction("}", "<Plug>(ParagraphNextMotion)", keepDefaultMapping = true) {
      moveParagraph(1)
    }
    // ... operator-pending mode mappings with omapPluginAction
  }
}

Defining Helper Functions

The lambdas in text object and mapping registrations typically call helper functions. Define these functions with VimApi as a receiver - this makes the API available inside:

// From VimIndentObject.kt
private fun VimApi.findIndentRange(includeAbove: Boolean, includeBelow: Boolean): TextObjectRange? {
  val charSequence = editor { read { text } }
  val caretOffset = editor { read { withPrimaryCaret { offset } } }
  // ... implementation using API
}

// From ParagraphMotion.kt
internal fun VimApi.moveParagraph(direction: Int) {
  val count = getVariable<Int>("v:count1") ?: 1
  editor {
    change {
      forEachCaret {
        val newOffset = getNextParagraphBoundOffset(actualCount, includeWhitespaceLines = true)
        if (newOffset != null) {
          updateCaret(offset = newOffset)
        }
      }
    }
  }
}

API Features

How to Migrate Existing Extensions

What Stays the Same

• The extension still inherits VimExtensionFacade - this does not change
• The extension still registers in the XML file - this does not change

Migration Steps

Step 1: Ensure Test Coverage

Before starting migration, make sure tests exist for the extension:

• Tests should work and have good coverage
• If there aren't enough tests, create more tests first
• Verify tests pass on the existing version of the plugin

Step 2: Migrate in Small Steps

• Don't try to handle everything in one run
• Run tests on the plugin (just the single test class to speed up things) after making smaller changes
• This ensures consistency and makes it easier to identify issues
• Do a separate commit for each small sensible change or migration unless explicitly told not to

Step 3: Migrate Handlers One by One

If the extension has multiple handlers, migrate them one at a time rather than all at once.

Step 4: Handler Migration Process

For each handler, follow this approach:

1. Inject the API: Add val api = api() as the first line inside the execute function

2. Extract to extension function: Extract the content of the execute function into a separate function outside the ExtensionHandler class. The new function should:

   • Have VimApi as a receiver
   • Use the api that was obtained before
   • Keep the extraction as-is (no changes to logic yet)

3. Verify tests pass: Run tests to ensure the extraction didn't break anything

4. Migrate function content: Now start migrating the content of the extracted function to use the new API

5. Verify tests pass again: Run tests after each significant change

6. Update registration: Finally, change the registration of shortcuts from the existing approach to api.mappings { } where you call the newly created function

Example Migration Flow

// BEFORE: Old style handler
class MyHandler : ExtensionHandler {
  override fun execute(editor: VimEditor, context: ExecutionContext, operatorArguments: OperatorArguments) {
    // ... implementation
  }
}

// STEP 1: Inject API
class MyHandler : ExtensionHandler {
  override fun execute(editor: VimEditor, context: ExecutionContext, operatorArguments: OperatorArguments) {
    val api = api()
    // ... implementation
  }
}

// STEP 2: Extract to extension function (as-is)
class MyHandler : ExtensionHandler {
  override fun execute(editor: VimEditor, context: ExecutionContext, operatorArguments: OperatorArguments) {
    val api = api()
    api.doMyAction(/* pass needed params */)
  }
}

private fun VimApi.doMyAction(/* params */) {
  // ... same implementation, moved here
}

// STEP 3-5: Migrate content to new API inside doMyAction()

// STEP 6: Update registration to use api.mappings { }
override fun init() {
  val api = api()
  api.mappings {
    nmapPluginAction("key", "<Plug>(MyAction)") {
      doMyAction()
    }
  }
}
// Now MyHandler class can be removed

Handling Complicated Plugins

For more complicated plugins, additional steps may be required.

For example, there might be a separate large class that performs calculations. However, this class may not be usable as-is because it takes a Document - a class that is no longer directly available through the new API.

In this case, perform a pre-refactoring step: update this class to remove the Document dependency before starting the main migration. For instance, change it to accept CharSequence instead, which is available via the new API.

Final Verification: Check for Old API Usage

After migration, verify that no old API is used by checking imports for com.maddyhome.

Allowed imports (these are still required):

• com.maddyhome.idea.vim.extension.VimExtension
• com.maddyhome.idea.vim.extension.api

Any other com.maddyhome imports indicate incomplete migration.