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prettier-plugin-sieve

A Prettier plugin for formatting Sieve email filtering scripts (RFC 5228).

Features

• Formats .sieve / .siv files via Prettier • Hand-rolled Peggy.js PEG grammar for RFC 5228 core language • Supports: require, if/elsif/else, all standard tests (address, header, envelope, allof, anyof, not, size, exists, true, false), all standard actions (fileinto, redirect, keep, discard, stop, reject, vacation, addflag, setflag, removeflag) • Idempotent — formatting twice gives the same result • Works with Prettier 3.x • IntelliJ IDEA + VS Code Prettier extension compatible

Installation

Configuration

.prettierrc

VS Code (settings.json)

IntelliJ IDEA

Go to Settings → Languages & Frameworks → JavaScript → Prettier:

• Enable "Run on save" • Add **/*.sieve to the "Run for files" glob

Usage

Example

Input (messy):

Output (formatted):

Project Structure

Architecture

1 · Grammar (src/parser/sieve.pegjs)

A Peggy PEG grammar that directly encodes RFC 5228 syntax. Each grammar rule returns a typed AST node with a loc (source location) property. The grammar is compiled at runtime the first time parse() is called (or can be pre-compiled via npm run generate-parser for production builds).

2 · Parser adapter (src/parser/index.ts)

Wraps Peggy's parse() to:

• Return a Script root node • Expose locStart / locEnd so Prettier can attach comments • Surface grammar errors with human-readable messages

3 · Printer (src/printer.ts)

Converts the Sieve AST into Prettier's Doc IR using the doc.builders API:

| Doc primitive | Where used |

| hardline | Between top-level commands and block contents | | softline | Inside string lists, test argument lists | | group | All commands and tests — allows line-breaking when over printWidth | | indent | Block bodies, multi-line list arguments | | join | Comma-separated string lists and test lists |

Building

Testing

Extending

To add support for Sieve extensions (e.g. RFC 5232 sieve-imap-flags, RFC 5230 vacation):

1. Add new rules to src/parser/sieve.pegjs 2. Add new AST interfaces to src/types.ts 3. Add case branches to printAction / printTest in src/printer.ts

License

MIT