Extend the Default attribute to support multiple bindings declarations with parameter packs.

[SouHanaQiao]

1. Extend the Default attribute by parameter packs like this:

@attached(peer) @available(swift 5.9) public macro Default<each T>(_ defaults: repeat each T) = #externalMacro(module: "MacroPlugin", type: "Default")

So we can set default values ​​for multiple bindings variables.

Example:

struct Student { @Default("Simon", 22, 99) let name: String, age: Int, grade: Int enum Gender: Codable { case male case female } @Default(Gender.female, 13) let gender: Gender, `class`: Int }

Equivalent to:

struct Student { @Default("Simon") let name: String @Default(22) let age: Int @Default(99) let grade: Int enum Gender: Codable { case male case female } @Default(Gender.female) let gender: Gender @Default(13) let `class`: Int }

2. Default attribute parameter number diagnostics.

1. Some default value parameters are missing:

struct SomeCodable1 { @Default() /// @Default missing default value for variable 'one' let one: String } struct SomeCodable2 { @Default("hello") /// @Default missing default values for variables 'tow', 'three' let one: String, tow: Int, three: Float }

2. Too many default value parameters:

struct SomeCodable1 { @Default("hello", 10) /// @Default expect 1 default value but found 2 ! let one: String } struct SomeCodable2 { @Default("hello", 10, 1, 2, 3) /// @Default expect 2 default values but found 5 ! let one: String, tow: Int }