[Feature Request]: Per-window buffer scoping (Split-local buffers via Winbar)

[YousefHadder]

What?

I would like to propose adding support for per-window buffer scoping by allowing bufferline.nvim to render inside Neovim's winbar.

Currently, bufferline.nvim renders to the global tabline. This feature would allow users to have a dedicated buffer line for each split (window), containing only the buffers relevant to that specific split.

Proposed Functionality:

1. Rendering Target: Add an option to render the bufferline component in the native winbar instead of (or in addition to) the tabline.
2. Per-Window Scope: When in winbar mode, the plugin would maintain a list of buffers specific to that window ID, rather than showing all globally open buffers.
   • Behavior: When a user opens a file in Split A, it is added to Split A's buffer list.
   • Navigation: Commands like :BufferLineCycleNext would operate within the context of the current window's buffer list only.
3. Visuals: Each split would effectively have its own "tab bar" at the top, showing only the files being worked on in that context.

Example Scenario:

• Left Split (Feature Work): Shows feature.lua, utils.lua, types.lua.
• Right Split (Tests): Shows feature_spec.lua, helpers_spec.lua.
• Cycling buffers in the right split only rotates through the test files, leaving the left split's context irrelevant.

Why?

1. Solves the "Global Buffer Soup" Problem:
Neovim's default buffer system is global. When working with multiple splits (e.g., code on the left, tests on the right), the buffer list becomes a mix of unrelated files. Switching buffers often accidentally pulls a test file into the code split, breaking layout and mental context.

2. Improved Context Tracking:
Users often use splits to separate concerns (Frontend vs Backend, Code vs Tests). A global bufferline does not reflect this workflow. Per-window scoping allows the UI to match the user's mental model: "These are the files I am using here."

3. Native 'Winbar' Utilization:
Since Neovim 0.8+, the winbar option allows for window-local status lines. This is the perfect architectural place for this feature, as it is inherently scoped to the window, whereas the tabline is global.

4. Alternatives are Lacking:
While plugins like scope.nvim offer tab-scoped buffers, there is currently no robust solution for split-scoped buffers with visual indication. Implementing this in bufferline.nvim would make it the definitive tool for complex window layouts.

[YousefHadder]

@akinsho I can dive more into the codebase and edge cases to find out if this will introduce any issues for users.

It shouldn't be a breaking change, where users can enable it in config without affecting other functionalities.

Alternative Proposal

I'm exploring an alternative approach: instead of adding all the window-scoping logic directly to bufferline, I could:

1. Add a minimal extension hook to bufferline (~10 lines)
2. Implement window-local buffer tracking in a separate companion plugin

This would keep bufferline lean while still enabling the functionality. Thoughts?

[mathiaslovnes]

I would love to see this feature implemented! 🙏