Sake Macro Development

Sake Macro Development

Reference for working on the @CommandGroup Swift macro.

What the Macro Does

@CommandGroup is an ExtensionMacro that generates:

1. CommandGroup protocol conformance
2. A commands computed property — dictionary of all public static Command vars

// Input
@CommandGroup
struct MyCommands {
    public static var hello: Command { ... }
    public static var bye: Sake.Command { ... }
    static var internal: Command { ... }       // excluded: not public
    private var foo: Command { ... }           // excluded: not public, not static
}

// Generated
extension MyCommands: Sake.CommandGroup {
    static var commands: [String: Sake.Command] {
        ["hello": Self.hello, "bye": Self.bye]
    }
}

Inclusion Criteria

A property is included in commands only if ALL of:

• Has public modifier
• Has static modifier
• Type annotation is exactly Command or Sake.Command

Typealiases, inferred types, or other spellings are NOT detected.

Implementation

File: Sources/SakeMacros/SakeAppMacro.swift

public struct CommandGroupMacro: ExtensionMacro {
    public static func expansion(...) throws -> [ExtensionDeclSyntax] {
        // 1. Filter members: public + static
        // 2. Check type annotation: Command or Sake.Command
        // 3. Extract variable names
        // 4. Generate dictionary literal
        // 5. Return extension with CommandGroup conformance
    }
}

Plugin registration: Sources/SakeMacros/Plugin.swift

SwiftSyntax Patterns Used

• declaration.memberBlock.members — iterate struct members
• .compactMap { $0.decl.as(VariableDeclSyntax.self) } — get variable declarations
• $0.modifiers.map(\.name.text) — check access modifiers
• binding.typeAnnotation?.type.as(IdentifierTypeSyntax.self) — simple type (Command)
• binding.typeAnnotation?.type.as(MemberTypeSyntax.self) — qualified type (Sake.Command)
• binding.pattern.as(IdentifierPatternSyntax.self)?.identifier.text — variable name
• ExtensionDeclSyntax("""...""") — string interpolation for generating syntax

Testing

File: Tests/SakeMacrosTests/SakeAppMacroTests.swift

Uses SwiftSyntaxMacrosTestSupport:

import SakeMacros
import SwiftSyntaxMacrosTestSupport

assertMacroExpansion(
    """
    @CommandGroup
    struct MyCommands {
        public static var hello: Command { ... }
    }
    """,
    expandedSource: """
    struct MyCommands {
        public static var hello: Command { ... }
    }

    extension MyCommands: Sake.CommandGroup {
        static var commands: [String: Sake.Command] {
            ["hello": Self.hello]
        }
    }
    """,
    macros: ["CommandGroup": CommandGroupMacro.self],
)

Key test cases:

• Multiple commands with mixed visibility (public, private, static, non-static)
• Both Command and Sake.Command type annotations
• Zero commands → generates [:]

Dependencies

// Package.swift
.macro(name: "SakeMacros", dependencies: [
    .product(name: "SwiftSyntaxMacros", package: "swift-syntax"),
    .product(name: "SwiftCompilerPlugin", package: "swift-syntax"),
])

swift-syntax version: 602.0.0+

Source: kattouf/Sake — distributed by TomeVault.