feat: add module rename support

[scottming]

Context

While AI-assisted renaming is convenient, it's still slower than a native Language Server implementation. This PR ports the module rename feature from Lexical PR #636, which I've been using reliably for almost two years. Given that the Lexical repository is now archived, I wanted to bring this practical and well-tested feature to Expert.

Changes

Core Implementation (engine)

• Add Engine.CodeMod.Rename module with submodules: Prepare, Module, Entry, File, and Diff
• Add Engine.Commands.Rename GenServer for tracking rename progress and triggering reindex
• Add Engine.Commands.RenameSupervisor for managing rename command lifecycle

LSP Integration (expert)

• Add PrepareRename and Rename handlers for LSP protocol
• Extend Expert.EngineApi with prepare_rename/3 and rename/5 APIs
• Register rename_provider with prepare_provider: true in server capabilities

Infrastructure (forge)

• Add RenameFile struct to Forge.Document.Changes for file rename operations
• Add file_changed and file_saved message types to Forge.EngineApi.Messages

Key Differences from Lexical

• Uses :erpc.call via Expert.EngineApi.call/4 instead of RemoteControl.call
• Added reindexing mechanism after rename to keep search index consistent (see "Why These Changes")
• Namespace mapping: Lexical.RemoteControl.* → Engine.*, Lexical.Server.* → Expert.*

Why These Changes

• Progress tracking & reindex (59953157): Without reindexing after rename, the search index retains old module names. This causes subsequent renames to fail - e.g., renaming Accounts → Accounts2 works, but renaming back fails because the index doesn't reflect the new names.

• Temporary document opening (f08fd155): After a file rename, the new URI may not exist in Document.Store, causing "not_open" errors during reindex. Added ensure_open/1 to temporarily open files from disk when needed.

• Expanded test coverage (a38652ef): Added comprehensive tests covering references, descendants, structs, edge cases, and file renaming with realistic module names.

Extra

A demo video is attached showing the smooth rename workflow - renaming a module and then renaming it back. Tested successfully in both VSCode and Neovim.

CleanShot.2026-01-04.at.15.43.19.mp4

[doorgan]

Some notes(I'm testing on a brand new mix phx.new rename_test project:

• If I am on module RenameTestWeb.Router and I rename it to ExpertRenameTestWeb then

  • No other module prefixed with RenameTestWeb is renamed
  • The use RenameTestWeb, :router isn't renamed either

• If I create lib/rename_test/nested/foo.ex defining RenameTest.Nested.Foo and I rename RenameTest in lib/rename_test.ex, then the child modules are renamed and the files are renamed too, but I end up with an empty lib/rename_test/nested folder

• When I try to rename a function(I know this is not supported by this PR, but still) I get this error:

2026-01-14 16:34:27.690 [info] [Error - 4:34:27 PM] ** (UndefinedFunctionError) function XPGenLSP.ErrorResponse.fetch/2 is undefined (XPGenLSP.ErrorResponse does not implement the Access behaviour

You can use the "struct.field" syntax to access struct fields. You can also use Access.key!/1 to access struct fields dynamically inside get_in/put_in/update_in)
    (xp_gen_lsp 0.11.2) XPGenLSP.ErrorResponse.fetch(%XPGenLSP.ErrorResponse{message: "Failed to handle textDocument/prepareRename, {:error, :request_failed, \"Renaming :call is not supported for now\"}", code: -32603, data: nil}, :placeholder)
    (elixir 1.17.2) lib/access.ex:322: Access.get/3
    (xp_schematic 0.2.1) lib/schematic.ex:608: anonymous fn/5 in XPSchematic.map/1
    (elixir 1.17.2) lib/enum.ex:2531: Enum."-reduce/3-lists^foldl/2-0-"/3
    (xp_schematic 0.2.1) lib/schematic.ex:583: anonymous fn/3 in XPSchematic.map/1
    (xp_schematic 0.2.1) lib/schematic.ex:1001: anonymous fn/4 in XPSchematic.telemetry_wrap/3
    (xp_telemetry 1.3.0) /Users/dorgan/dev/expert/apps/expert/deps/telemetry/src/telemetry.erl:324: :xp_telemetry.span/3
    (xp_schematic 0.2.1) lib/schematic.ex:947: anonymous fn/3 in XPSchematic.oneof/1

Also we should have some progress reported, I'm testing on VSCode(it's easier for me to trigger these actions from this editor) and I don't see progress reported there, neither in the status bar nor in the Expert logs there

[scottming]

Hi, @doorgan Thanks for the detailed feedback! Let me address each point:

1. Renaming RenameTestWeb.Router to ExpertRenameTestWeb

This is actually the expected behavior by design. The current rename implementation renames:

• The exact module and all its references
• Descendant modules (e.g., MyApp.Users.Query when renaming MyApp.Users)

When you rename RenameTestWeb.Router, other modules like RenameTestWeb.PageController are not descendants of Router, so they won't be renamed. Similarly, use RenameTestWeb, :router references the RenameTestWeb module, not RenameTestWeb.Router.

If you want to rename the RenameTestWeb prefix across all modules, you should trigger the rename on the defmodule RenameTestWeb definition itself.

2. Empty folder left after renaming

Good catch! This is a known limitation. The file rename operation is actually executed by the editor (VSCode/Neovim) via LSP's RenameFile - the editor handles creating parent directories automatically, but it doesn't clean up empty source directories afterward.

To fix this, we'd need to detect which directories become empty after the rename and send additional DeleteFile operations for them. Given that the rename feature is already quite complex (handling module references, descendants, file path conventions, Phoenix special folders, progress tracking, etc.), I'll note this as a potential future improvement, but it's lower priority for now.

3. Error when trying to rename a function

You're right - even though function renaming isn't supported yet, it should return a friendly error message like "Renaming :function is not supported for now" rather than throwing an UndefinedFunctionError. I'll look into this over the weekend since this is a higher priority issue.

4. Progress reporting in VSCode

Thanks for flagging this. We do have progress reporting implemented with VSCode-specific handling, but it seems something might be off. I'll investigate this as well.

[scottming]

Hi, @doorgan — the third and fourth issues you mentioned should both be fixed now. Please take a look at the two latest commits; they include detailed explanations of the problems and the solutions.