Unify language server with in-editor autocompletion provider

Describe the project you are working on

N/A

Describe the problem or limitation you are having in your project

The autocompletion in Godot's built-in editor and LSP seems to be running on very different logic, as evidenced by frequent unrelated autocomplete entries when using the LSP.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

This proposal aims to resolve the aforementioned disparity by having both the built-in editor and the LSP use the same source of autocompletions. This effectively dogfoods the autocompletion system and makes the LSP act more like an adapter, and also make tracking LSP-related bugs easier as there would no longer be two sources of autocompletion. This can also be expanded to cover symbol lookup and other LSP-related things, too.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Current implementation

graph TD
    subgraph "Godot Engine"
        A[GDScript]
        B[Built-in Autocomplete]
        C[Built-in Editor]
        D[LSP Server]

        A --> B --> C
        A --> D
    end

    E[External Editors]
    D --> E

Proposed implementation

graph TD
    subgraph "Godot Engine"
        A[GDScript]
        B["Unified Language Server
        (Autocomplete, symbols, types, rename)"]
        C[Built-in Editor]
        D[LSP Adapter]

        A --> B
        B --> C
        B --> D
    end

    E[External Editors]
    D --> E

If this enhancement will not be used often, can it be worked around with a few lines of script?

No.

Is there a reason why this should be core and not an add-on in the asset library?

Built-in editor and LSP server is core.

godotengine / godot-proposals