bug: formatter fails on paths with parentheses e.g. Next.js route groups (public)

[HiRahmatDev]

Neovim version (nvim -v)

NVIM v0.12.0

Operating system/version

Windows 11 (without WSL)

Read debugging tips

• I have read through the debugging tips.

Add the debug logs

• I have set log_level = vim.log.levels.DEBUG and pasted the log contents below.

Log file

Working (path without parentheses):

[DEBUG] Running formatters on C:/Users/.../src/app/error.tsx: { "prettier" }
[DEBUG] Run command: { "prettier.cmd", "--stdin-filepath", "C:/Users/.../src/app/error.tsx" }
[DEBUG] prettier exited with code 0

Failing (path with parentheses):

[DEBUG] Running formatters on C:/Users/.../src/app/(public)/download-app/page.tsx: { "prettier" }
[DEBUG] Run command: { "prettier.cmd", "--stdin-filepath", "C:/Users/.../src/app/(public)/download-app/page.tsx" }
[INFO] prettier exited with code 255
[DEBUG] prettier stdout: { '...> "node.exe" "prettier.cjs" --stdin-filepath C:/.../(public)/download-app/page.tsx' }
[DEBUG] prettier stderr: { "/download-app/page.tsx was unexpected at this time." }
[ERROR] Formatter 'prettier' error: /download-app/page.tsx was unexpected at this time.

Describe the bug

On Windows, conform.nvim fails to format files when the file path contains parentheses ( ).
This is a common scenario in Next.js App Router projects which use route groups, e.g. src/app/(public)/page.tsx.

The root cause is that conform.nvim spawns .cmd files directly (e.g. prettier.cmd).
Windows CMD treats ( and ) as reserved characters for group expressions (used in if, for, etc.).
When CMD encounters a path like (public) inside a .cmd execution chain, it misparses it as a group expression instead of a plain string — causing the formatter to fail.

What is the severity of this bug?

tolerable (can work around it)

Steps To Reproduce

1. Use Windows without WSL
2. Open a Next.js project that uses route groups, e.g. src/app/(public)/page.tsx
3. Trigger conform.nvim formatter (e.g. Prettier) on any file inside a route group folder
4. Formatter fails with exit code 255

Expected Behavior

Conform should handle Windows paths with special characters like ( ) correctly,
either by routing through PowerShell instead of CMD, or by properly escaping arguments before passing them to .cmd executables.

Minimal example file

File path:

src/app/(public)/download-app/page.tsx

File content:

export default function DownloadAppPage() {
  return <div>Download App</div>
}

Minimal init.lua

-- PLUGINS
--
-- See `:h :packadd`, `:h vim.pack`

-- Install third-party plugins via "vim.pack.add()".
vim.pack.add({
  -- LSP
  'https://github.com/neovim/nvim-lspconfig',
  'https://github.com/mason-org/mason.nvim',

  -- Formatter
  'https://github.com/stevearc/conform.nvim',
})

require('conform').setup({
  log_level = vim.log.levels.DEBUG,
  formatters_by_ft = {
    lua = { 'stylua' },
    json = { 'prettier' },
    html = { 'prettier' },
    css = { 'prettier' },
    javascript = { 'prettier' },
    javascriptreact = { 'prettier' },
    typescript = { 'prettier' },
    typescriptreact = { 'prettier' },
  }
})

vim.keymap.set({ 'n' }, ';f', require('conform').format)

Additional context

• This issue likely affects all Node.js-based formatters that use .cmd wrappers on Windows (e.g. eslint_d, biome, etc.)
• Native .exe formatters like stylua are not affected
• This does not affect Windows with WSL

[HiRahmatDev]

Update: Temporary Workaround

I managed to work around this issue by bypassing the .cmd wrapper entirely and calling node directly with the path to prettier's .cjs entry point.

This approach also handles both cases — whether prettier is installed locally in node_modules or globally via Volta.sh (C:\\Program Files\\Volta\\node.EXE):

require('conform').setup({
  ...
  formatters = {
    prettier = {
      command = 'node',
      args = function(_, ctx)
        local local_prettier = vim.fn.getcwd() .. '/node_modules/prettier/bin/prettier.cjs'
        local mason_prettier = vim.fn.stdpath('data')
          .. '/mason/packages/prettier/node_modules/prettier/bin/prettier.cjs'

        local prettier_path
        if vim.fn.filereadable(local_prettier) == 1 then
          prettier_path = local_prettier
        else
          prettier_path = mason_prettier
        end

        return {
          prettier_path,
          '--stdin-filepath',
          ctx.filename,
        }
      end,
    },
  },
  ...
})

By calling node directly, CMD is completely removed from the execution chain — so ( and ) in the path are never misinterpreted as group expressions.

Note: this workaround is specific to Node.js-based formatters. The core issue remains — conform should handle this case properly on Windows without requiring manual workarounds.