Dollup is a tool for formatting Swift source code. It automatically adjusts indentation, wraps lines to a specified maximum width, and enforces a consistent brace style, helping to maintain a readable code style.

Dollup supports Linux and macOS. We provide prebuilt binaries for several platforms.

Download the correct binary for your platform from the table above, extract it, and add the dollup binary to your PATH. The pre-built Linux binaries do not require the Swift runtime to be installed on the system.

To build the dollup executable, you will need the Swift 6.1 toolchain. Navigate to the project's root directory and run the following command:

swift build

The compiled executable will be located in the .build/debug directory.

To format a Swift file or all Swift files within a directory, run the dollup executable with the path to the file or directory as an argument:

swift run dollup [file-path]

This will reformat the specified file in place.

When a directory is provided, dollup will recursively format all .swift files within it.

Dollup is configured by creating a Swift executable that conforms to the DollupConfiguration protocol. This allows you to specify formatting options in a declarative way.

Here's an example of a simple configuration file:

import DollupConfig
import SystemPackage

@main enum Main: DollupConfiguration {
    public static func configure(file _: FilePath?, settings: inout DollupSettings) {
        settings.check = true
        settings.whitespace {
            $0.width = 96
            $0.braces = .egyptian

            $0.indent.spaces = 4
            $0.indent.ifConfig = false

            $0.formatColonPadding = true
            $0.keywordsOnSameLine = true
        }
    }

    public static func filter(file: FilePath) -> Bool {
        true // run on all files
    }
    public static func report(file: FilePath) {
        print("> reformatted '\(file)'")
    }
}

This configuration specifies that the code should be formatted with a maximum line width of 96 characters, Egyptian-style braces, and an indent width of 4 spaces. It also enables the integrity check, which ensures that the reformatted code is semantically equivalent to the original.

The dollup tool is built using SwiftSyntax to parse and transform Swift source code. It operates in several passes:

1. Line Expansion: The tool first ensures that code blocks with interior newlines are properly expanded, adding line breaks where necessary to enforce a consistent vertical layout.
2. Re-indentation: It then analyzes the code's structure to calculate the correct indentation level for each line, taking into account nested blocks, function calls, and other language constructs.
3. Line Wrapping: Finally, it iteratively wraps lines that exceed the specified maximum width, breaking long lines at appropriate points, such as after commas in argument lists or before operators in expressions.

The tool is designed to be robust and preserves the semantic meaning of the code throughout the formatting process. An integrity check is performed by default to verify that no unintended changes have been introduced.