Prettier Multiline Plugin

A Prettier plugin that formats imports, arrays, and objects on multiple lines to minimize merge conflicts in collaborative development environments.

Why Multi-line Formatting Matters

The Problem: Merge Conflicts in Collaborative Development

In large projects with multiple developers working simultaneously, merge conflicts are a common pain point that slow down development and integration. One of the most frequent sources of these conflicts is single-line formatting of imports, arrays, and objects.

Consider this common scenario:

1. Developer A adds a new import to a file:

   import { alpha, beta, delta, gamma } from 'module';

2. Meanwhile, Developer B also adds a different import to the same line:

   import { alpha, beta, epsilon, gamma } from 'module';

3. When merging these changes, a conflict occurs that must be manually resolved:

   <<<<<<< HEAD
   import { alpha, beta, delta, gamma } from 'module';
   =======
   import { alpha, beta, epsilon, gamma } from 'module';
   >>>>>>> feature-branch

These conflicts are:

• Time-consuming: Each must be manually resolved
• Error-prone: Easy to accidentally remove someone's import
• Frequent: Happens constantly in active projects

The Solution: Multi-line Formatting

By formatting imports, arrays, and objects with one item per line, merge conflicts become both less frequent and easier to resolve:

import {
  alpha,
  beta,
  delta,
  gamma,
} from 'module';

Benefits:

1. Reduced Conflict Frequency: Changes to different items won't conflict
2. Clearer Diffs: Git diffs show exactly which item was added/removed
3. Easier Resolution: When conflicts do occur, they're isolated to specific items
4. Better Code Reviews: Reviewers can clearly see which items were modified
5. Improved Maintainability: Easier to alphabetize or organize imports

Real-world Example

With single-line formatting:

- import { alpha, beta, gamma } from 'module';
+ import { alpha, beta, delta, gamma } from 'module';

If two developers add different items, this creates a merge conflict.

With multi-line formatting:

  import {
    alpha,
    beta,
+   delta,
    gamma,
  } from 'module';

Even if two developers add different items, Git can often auto-merge these changes without conflicts.

Installation

npm install --save-dev prettier-plugin-multiline

Usage

Configuration File

Add the plugin to your Prettier configuration:

{
  "plugins": ["prettier-plugin-multiline"],
  "multilineImports": true,
  "multilineArrays": true,
  "multilineObjects": true,
  "sortImports": true,
  "minItemsForMultiline": 2
}

Command Line

You can also use the plugin directly from the command line:

# Format with multiline imports
npx prettier --plugin=prettier-plugin-multiline --parser=typescript --multiline-imports file.ts

# Format with sorted imports
npx prettier --plugin=prettier-plugin-multiline --parser=typescript --sort-imports file.ts

# Format with both multiline and sorted imports
npx prettier --plugin=prettier-plugin-multiline --parser=typescript --multiline-imports --sort-imports file.ts

# Set minimum items for multiline formatting
npx prettier --plugin=prettier-plugin-multiline --parser=typescript --multiline-imports --min-items-for-multiline=2 file.ts

Configuration Options

| Option | Type | Default | Description | |--------|------|---------|-------------| | multilineImports | boolean | false | Format imports on multiple lines | | multilineArrays | boolean | false | Format array literals on multiple lines | | multilineObjects | boolean | false | Format object literals on multiple lines | | sortImports | boolean | false | Sort import specifiers | | minItemsForMultiline | number | 1 | Minimum number of items to trigger multiline formatting | | debug | boolean | false | Enable debug output for the plugin |

Example Configuration

For optimal merge conflict reduction in large projects:

{
  "plugins": ["prettier-plugin-multiline"],
  "multilineImports": true,
  "multilineArrays": true,
  "multilineObjects": true,
  "minItemsForMultiline": 2
}

This configuration will format all imports, arrays, and objects with 2 or more items on multiple lines, significantly reducing merge conflicts in collaborative environments.

License

MIT