Work toward upstreaming of features from my fork

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Issue Details

History: I use YCM as a daily driver since many years.

However some time ago I tried to use coc.nvim and was using it for several years. However, after they broke something that I did not investigate, which blocked the ui and the editor became unresponsive (this happens on some very large repos) I switched back to YCM and was using since them. However, coc has some features, which are not available in YCM, notably document/highlighting or progress indicator and for some time it was very painful not to have them in YCM. I had some time during my vacation and decided to implement the below list of features in YCM to have feature parity with coc.

Below you could find a list of features that are currently reside inside my fork. I would like to upstream them into the main YCM, such that I do not need to maintain my own fork. Since the below list is quite large I did not want to open a lot of PRs first and wanted to have your opinion first, of whether it is in principle interesting for the project.

If so then I would like to develop some plan on how can we proceed here.

The code in my fork is developed with the help of gpt 5.6 sol, however I do not consider it as AI slop. During development I used the standard approach that I use during my daily work. I reviewed all the changes and guided the development in the direction I like. I invested quite a lot of hours into the below work. Thus the list of changes is not governed by some promt: "go and implement the feature X" without any supervision or review.

Below is the list of changes:

YouCompleteMe changes

1. Work-done progress UI

   • Track concurrent progress operations.
   • Display progress and an animated spinner through youcompleteme#GetStatus().
   • Emit YcmStatusChanged for statusline integrations.
   • Associate progress with ycmd connection generations.
   • Clear stale progress after crashes, restarts, and explicit server shutdown.
   • Correctly display zero percent and empty report messages.

2. Neovim feature parity and UI abstraction

   Editor-independent controllers were separated from editor-specific rendering. Vim retains its popup/text-property implementations, while Neovim uses floating windows and extmarks.

   Added or completed Neovim support for:

   • Hover
   • Inlay hints
   • Semantic highlighting
   • Symbol finder
   • Type and call hierarchy
   • Detailed diagnostic popups
   • Diagnostic virtual text
   • Signature help
   • Completion information popups

   Shared list rendering is reused by finder and hierarchy.

3. Vim/Neovim integration-test parity

   • Reorganized tests into test/shared, test/vim, and test/neovim.
   • All 16 portable integration suites now have Vim and Neovim entry points.
   • Vim has one additional runner-specific suite.
   • Added editor adapters instead of duplicating behavioral test bodies.
   • Expanded finder, hierarchy, hover, diagnostics, semantic-highlighting, inlay-hint, and signature-help coverage.

4. Request cancellation

   • Added a shared operation manager and cancellable HTTP requests.

   • Integrated cancellation into completion, completion-item resolution, signature help, semantic tokens, inlay hints, commands, hierarchy operations, and FixIt resolution.

   • Preserve pending scrolling-range requests when they still cover the viewport.

   • Cancel requests when their document snapshot or visible range becomes obsolete.

   • Added client-side tracing correlated with ycmd tracing.

   Commits: 36cbdaefb through 458377711.

5. Automatic document highlighting

   • Request highlights after CursorHold.

   • Track buffer number, changed tick, and cursor position.

   • Cancel or discard stale results.

   • Render with Vim text properties and Neovim extmarks.

   • Use isolated decorations so cleanup does not affect other features.

   • Keep document highlights above semantic highlighting and visible over Vim’s CursorLine.

   • Avoid duplicate requests and flicker after scrolling when the document and cursor snapshot are unchanged.

   • Provide global and buffer-local enablement options.

   • Add shared Vim/Neovim integration tests and documentation.

   Commits: cd2965437 through c633fc456.

6. Supporting fixes and infrastructure

   • Fixed asynchronous finder request filtering and cursor-position races.
   • Fixed hierarchy redraw and kept its window visible during slow resolution.
   • Fixed polling of completed scrolling-range requests.
   • Stabilized completion tests against asynchronous clangd indexing.
   • Made diagnostic popup tests independent of Vim 9.1.0949 layout changes.
   • Fixed Vim test discovery for functions declared with abort.
   • Centralized Vim/Neovim feature-version checks.
   • Made documentation generation reproducible through Docker.
   • Updated README and generated Vim help for Neovim support and new features.

ycmd changes

1. LSP work-done progress

   • Advertise work-done progress support.
   • Handle progress-token creation and validate begin/report/end transitions.
   • Forward progress notifications to clients.
   • Tag progress with language-server connection generations.
   • Emit cleanup markers when a connection terminates or is replaced.
   • Return cleanup metadata from StopServer.
   • Avoid additional pending state or locking by making generation-tagged cleanup idempotent.

   Commits: 000d4f3e through 4acdfaf6.

2. Content-modified retries

   • Fix retry handling for semantic-token and inlay-hint requests.
   • Rebuild retries with fresh JSON-RPC IDs.
   • Retry only ContentModified, with bounded attempts.

   Commit: 728980ac.

3. Transport safety and generic cancellation

   • Serialize complete TCP writes so concurrent partial writes cannot corrupt the JSON-RPC stream.

   • Introduce operation-scoped cancellation contexts.

   • Allow one client operation to own multiple downstream LSP request IDs.

   • Support $ /cancelRequest, including cancellation arriving before request registration.

   • Retire old cancellation state using a monotonic watermark.

   • Expose cancellation through optional HTTP metadata and an endpoint.

   • Preserve compatibility for other ycmd clients: requests without operation metadata use the original path.

   • Add debug tracing that correlates client operation IDs, handlers, and LSP request IDs.

   Commits: 66284f16 through 5e606fca.

4. LSP document highlights

   • Advertise document-highlight client support.
   • Send textDocument/documentHighlight using UTF-16 positions.
   • Convert returned ranges to YCM byte-based coordinates.
   • Preserve Text, Read, and Write kinds and normalize missing or unknown kinds to Text.
   • Handle unsupported servers and null responses with stable empty results.
   • Apply ContentModified retries and generic cancellation.
   • Expose a cancellable /document_highlights endpoint.

   Commit: b3cfc851.