Fix prettier config resolution when no prettierFilePath is provided

[Copilot]

Problem

The prettier config resolution was failing when no prettierFilePath option was explicitly provided in the plugin configuration. This affected users who expected the plugin to automatically discover prettier config files (.prettierrc.json, .prettierrc.yml, etc.) in their project root.

Root Cause

The issue was in the fallback behavior in src/index.ts. When option.prettierFilePath was not provided, the code fell back to using config.root (a directory path):

const prettierOptions = 
  (await resolveConfig(option.prettierFilePath || config.root)) || {}

However, prettier.resolveConfig() expects a file path to search from, not a directory path. When passed a directory directly, it returns null, causing prettier configuration to be ignored.

Solution

Modified the fallback to provide a file path within the project root instead of the directory itself:

const prettierOptions =
  (await resolveConfig(
    option.prettierFilePath || join(config.root, 'package.json')
  )) || {}

This allows prettier to properly search for configuration files starting from the project root when no explicit prettierFilePath is provided.

Testing

• ✅ Direct .json config files work when specified via prettierFilePath
• ✅ Direct .yml config files work when specified via prettierFilePath
• ✅ Direct .cjs config files continue to work (no regression)
• ✅ Fallback behavior now correctly discovers config files in project root
• ✅ Plugin initializes successfully with all config formats
• ✅ No breaking changes to existing functionality

Changes

• Added import for join from node:path
• Updated fallback logic to use join(config.root, 'package.json') instead of config.root
• Total: 2 lines added, 1 line modified (minimal surgical change)

Fixes #113.

Warning

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