vim.lsp.config() completely ovewrites RA settings provided by Rustaceanvim rather than being merged

[WieeRd]

Checked other resources

• This is not a bug report or feature request (Please use issues for those).
• This is a question about rustaceanvim, not rust-analyzer or Neovim.
• This is not a question about autocompletion.
• I have read the README.
• I have read the FAQ.
• I have searched for a solution using :h rustaceanvim.
• I have searched existing discussions.
• I have searched the existing issues/discussions of other plugins related to this question (if applicable).
• I have searched the existing rust-analyzer discussions (if applicable).
• I have added a very descriptive title to this question.

Description

When providing RA settings using g:rustaceanvim, it is merged with the defaults provided by the plugin such as setting check.command to clippy. However, when I moved the settings to the lsp/ directory, it completely overwrote the settings instead of being merged with the defaults provided by the plugin. I expected it to work similarly to g:rustaceanvim.

Opening this as a discussion rather than an issue because I'm not sure if this was intended or not. Although I do believe it is more correct to have the configs merged since the intention of the vim.lsp.config API was to provide an easy way to manage and merge multiple layers of configs.

Here are :LspInfo results from 3 different setups:

Without any config

- Settings: {
    ["rust-analyzer"] = {
      check = {
        command = "clippy",
        extraArgs = { "--no-deps" }
      },
      checkOnSave = true
    }
  }

Using g:rustaceanvim

vim.g.rustaceanvim = {
  server = {
      default_settings = {
          ["rust-analyzer"] = {
              cargo = { features = "all" },
          },
      },
  },
}

 - Settings: {
     ["rust-analyzer"] = {
+       cargo = {
+         features = "all"
+       },
       check = {
         command = "clippy",
         extraArgs = { "--no-deps" }
       },
       checkOnSave = true
     }
   }

Using vim.lsp.config() or lsp/*.lua

vim.lsp.config("rust-analyzer", {
  settings = {
    ["rust-analyzer"] = {
        cargo = { features = "all" },
    },
  },
})

-- or

-- `~/.config/nvim/after/lsp/rust-analyzer.lua`
return {
  settings = {
    ["rust-analyzer"] = {
      cargo = { features = "all" },
    },
  },
}

- Settings: {
    ["rust-analyzer"] = {
      cargo = {
        features = "all"
      }
    }
  }

Example Code

require('lazy.minit').repro {
  spec = {
    {
      'mrcjkb/rustaceanvim',
      version = '^8',
      init = function()
        vim.lsp.config("rust-analyzer", {
          settings = {
            ["rust-analyzer"] = {
              cargo = { features = "all" },
            },
          },
        })
      end,
      lazy = false,
    },
  },
}

Neovim version (nvim -v)

NVIM v0.11.6

Operating system/version

Arch Linux

Output of :checkhealth rustaceanvim

rustaceanvim:                                                               ✅

Checking for Lua dependencies ~
- ✅ OK optional dependency nvim-dap not installed. Needed for debugging features [mfussenegger/nvim-dap](https://github.com/mfussenegger/nvim-dap)

Checking external dependencies ~
- ✅ OK rust-analyzer: found rust-analyzer 1 (7cb789d982 2026-02-01)
- ✅ OK Cargo: found cargo 1.93.1 (083ac5135 2025-12-15) (Arch Linux rust 1:1.93.1-1)
- ✅ OK rustc: found rustc 1.93.1 (01f6ddf75 2026-02-11) (Arch Linux rust 1:1.93.1-1)

Checking config ~
- ✅ OK No errors found in config.

Checking for conflicting plugins ~
- ✅ OK No conflicting plugins detected.

Checking for tree-sitter parser ~
- ✅ OK tree-sitter parser for Rust detected.

[mrcjkb]

This is a bug. Thanks for reporting 🙏
Created an issue: #979