Sieve Complete — Syntax Highlighting and Formatter

A VS Code extension that provides syntax highlighting and auto-formatting for Sieve email filter scripts — useful if you manage Proton Mail rules (or any other Sieve-based filter system) in a git repository.

Features

Syntax highlighting

Full TextMate grammar covering:

Control keywords: if, elsif, else, require
Actions: fileinto, redirect, keep, discard, stop, reject, vacation, notify, and more
Tests: address, header, envelope, size, exists, allof, anyof, body, date, and more
Tagged arguments: :is, :contains, :matches, :localpart, :domain, etc.
String literals with escape sequences
Block comments (/* ... */) and line comments (#)
Numeric literals with quantifiers (K, M, G)

Trailing comma removal

Removes trailing commas from string lists so you don't have to think about them while writing rules:

# Before
require ["fileinto", "imap4flags",];

# After
require ["fileinto", "imap4flags"];

Multi-line list expansion

Lists with 2 or more items are automatically expanded to one-item-per-line, making git diffs much cleaner:

# Before
if address :is "From" ["alice@example.com", "bob@example.com"] {

# After
if address :is "From" [
  "alice@example.com",
  "bob@example.com"
] {

require is left on a single line by default — see Settings to opt it in.

Block indentation

Re-indents if, elsif, and else block bodies based on {/} nesting depth:

# Before
if header :contains "Subject" "spam" {
discard;
} elsif address :is "From" "boss@example.com" {
fileinto "Important";
} else {
keep;
}

# After
if header :contains "Subject" "spam" {
  discard;
} elsif address :is "From" "boss@example.com" {
  fileinto "Important";
} else {
  keep;
}

Interior lines of /* ... */ block comments are preserved verbatim.

`} elsif` / `} else` joining

Merges a lone } onto the same line as a following elsif or else, consuming any blank lines between them:

# Before
}
elsif address :is "From" "boss@example.com" {

# After
} elsif address :is "From" "boss@example.com" {

Blank line normalisation

Collapses runs of more than one consecutive blank line into a single blank line.

All transformations run when you format a document (Shift+Alt+F / Format Document) or on save when Format On Save is enabled.

Settings

Setting	Default	Description
`sieve.formatter.expandLists`	`true`	Expand string lists with 2 or more items to one-item-per-line, and normalise indentation of already-multi-line lists. Disable to leave all list formatting untouched.
`sieve.formatter.alwaysExpandRequire`	`false`	Apply the same expansion rule to `require [...]`. Single-item `require` is never expanded. Has no effect when `expandLists` is disabled.
`sieve.formatter.indentBlocks`	`true`	Re-indent the contents of `if`, `elsif`, and `else` blocks based on brace nesting depth.
`sieve.formatter.joinElsifElse`	`true`	Join a lone `}` line with a following `elsif` or `else` onto the same line.
`sieve.formatter.normalizeBlankLines`	`true`	Collapse runs of more than one consecutive blank line into a single blank line.
`sieve.formatter.sortRequire`	`false`	Sort extensions inside `require [...]` alphabetically. Has no effect on a bare `require "string"` or a single-extension list.

The indentation inside expanded lists and block bodies respects your VS Code editor settings (spaces vs. tabs, tab size).

Usage

Install the extension
Open a .sieve file
Format with Shift+Alt+F (or enable Format On Save in VS Code settings)

Development

See CLAUDE.md for full development guidance. Quick start:

npm install
npm run compile   # build
npm test          # run unit tests
npm run lint      # lint

Press F5 to launch an Extension Development Host with the extension loaded.

Sieve Complete

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