feat: add prepend_to_file tool for prepending content to files

[amittell]

Add prepend_to_file Tool for Prepending Content to Files

Context

Adding a new prepend_to_file tool to complement the existing append_to_file tool. This provides a more efficient and explicit way to add content to the beginning of files, such as license headers, import statements, and configuration blocks.

Implementation

• Created a new tool modeled after the existing append_to_file tool with the key difference being content placement
• Implemented special handling for empty files to prevent unnecessary newlines
• Added comprehensive tests including various edge cases (empty files, different line endings, license headers)
• Integrated with existing components:
  • Updated tool registry in src/shared/tools.ts
  • Updated documentation in src/core/prompts/tools/prepend-to-file.ts
  • Updated Cline handler cases in src/core/Cline.ts
  • Updated schema definitions in src/schemas/index.ts
• Improved overall system documentation to include clear guidance on when to use prepend vs. append tools

Screenshots

No UI changes - this PR adds a new tool accessible through the AI interface.

How to Test

1. Use the AI to add a license header to a file:

   Add a license header to src/example.js
   

2. The AI should recommend using the prepend_to_file tool:

   <prepend_to_file>
   <path>src/example.js</path>
   <content>
   /**
    * Copyright (c) 2025 Roo Veterinary Inc.
    * 
    * This source code is licensed under the MIT license found in the
    * LICENSE file in the root directory of this source tree.
    */
   
   </content>
   </prepend_to_file>
   

3. Verify the content is added to the beginning of the file

4. Also test with an empty file to verify only the content is added without extra newlines

---

Important

Introduces prepend_to_file tool to prepend content to files, with integration, testing, and error handling updates.

• Behavior:
  • Adds prepend_to_file tool to prepend content to files, handling empty files and different line endings.
  • Handles special content formats like code block markers and HTML entities.
• Integration:
  • Updates tools.ts, index.ts, and rules.ts to include prepend_to_file.
  • Adds getPrependToFileDescription() in prepend-to-file.ts.
• Testing:
  • Adds prependToFileTool.test.ts for testing various cases like empty files, line endings, and error handling.
• Error Handling:
  • Validates access using rooIgnoreController and handles missing parameters.

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[changeset-bot]

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[ellipsis-dev]

Possible issue: using relPath.toPosix() assumes that relPath is an object with a .toPosix() method, but it's defined as a string. Consider using a proper path conversion helper (e.g., path.posix.normalize(relPath)) to ensure cross-platform compatibility.

[ellipsis-dev]

Consider refactoring: there is duplicated logic in handling partial updates versus full updates for prepending content. Extracting the common logic into a helper function would improve maintainability and reduce code duplication.

[ellipsis-dev]

A hardcoded delay of 300 ms is used after updating the diff view. This may be brittle in some environments; it would be better to either extract this value as a configurable constant or wait for a specific event/acknowledgment from the diff view for updates.

[mrubens]

I've been talking to @samhvw8 and we've been discussing just having one insert_content tool that can insert at the beginning, end, or any line within the file (and removing the append_to_file). I think that might be better than having a lot of special case tools, after discussing more. What do you think?

[mrubens]

I'm going to close this now that insert_content is available for everyone. Thank you for the contribution and pushing our thinking on this!