bug: prettier error being written to buffer

Reproduce the issue in Neovim using the provided Prettier configuration, an SCSS buffer, and a missing bracket. Start by tracing how the formatter handles stderr and the configured exit_codes; done means an exit code of 2 leaves the buffer unchanged. The payload names no repository file or test path.

Neovim version (nvim -v)

0.10.2

Operating system/version

macos 15

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

... filepath
[error] 1 |
[error] > 2 | <input css 1>
[error] | ^
[error] 3 | 13:5 ✖ Unknown word CssSyntaxError
[error] 4 |
[error] 5 | 1 problem (1 error, 0 warnings)

Describe the bug

When theres a syntax error, the error gets written to the buffer despite the exit code being 2 and me specifying 0,1.

What is the severity of this bug?

breaking (some functionality is broken)

Steps To Reproduce

open this as scss

nav {
ul {
margin: 0;
padding: 0;
list-style: none;
}

li { display: inline-block; }

a {
display: block;
padding: 6px 12px;
text-decoration: none;
}
}

then delete a bracket. Then try to format, the error gets written into the buffer

Expected Behavior

It should not modify the buffer because the exit code was 2.

Minimal example file

      prettier = {
        command = format_utils.from_node_modules("prettier"),
        args = function(self, ctx)
          local args = { "--stdin-filepath", "$FILENAME" }

          -- Get the current buffer's shiftwidth
          local shiftwidth = vim.bo.shiftwidth

          -- Determine if tabs or spaces are being used
          local use_tabs = vim.bo.expandtab == false

          -- Add indentation options
          table.insert(args, "--use-tabs")
          table.insert(args, tostring(use_tabs))
          table.insert(args, "--tab-width")
          table.insert(args, tostring(shiftwidth))

          -- Add config path if specified
          local config_path = format_utils.find_config_file("prettier", prettier_config_patterns, ctx)
          if config_path then
            table.insert(args, "--config")
            table.insert(args, config_path)
          end

          return args
        end,
        stdin = true,
        exit_codes = { 0, 1 },
        cwd = function()
          return file_utils.find_closest_node_modules_to_current_file()
        end,
        condition = function(_, ctx)
          return format_utils.formatter_condition("prettier", prettier_config_patterns, ctx)
        end,
      },

Minimal init.lua

No response

Additional context

No response