feat: added options for custom key case style (#18)

Author: soumyamahunt

.vscode/settings.json

@@ -5,5 +5,8 @@
         "**/.docc-build": true,
         "**/node_modules": true,
         "Package.resolved": true
-    }
+    },
+    "editor.unicodeHighlight.allowedCharacters": {
+        "－": true
+    },
 }

README.md

@@ -24,6 +24,7 @@ Supercharge `Swift`'s `Codable` implementations with macros.
 - Generates member-wise initializer(s) considering the above default value syntax as well.
 - Allows to create custom decoding/encoding strategies with ``HelperCoder`` and using them with ``CodedBy(_:)``. i.e. ``LossySequenceCoder`` etc.
 - Allows to ignore specific properties from decoding/encoding with ``IgnoreCoding()``, ``IgnoreDecoding()`` and ``@IgnoreEncoding()``.
+- Allows to use camel-case names for variables according to [Swift API Design Guidelines](https://www.swift.org/documentation/api-design-guidelines/#general-conventions), while enabling a type to work with different case style keys with ``CodingKeys(_:)``.
 - Allows to ignore all initialized properties of a type from decoding/encoding with ``IgnoreCodingInitialized()`` unless explicitly asked to decode/encode by attaching any coding attributes, i.e. ``CodedIn(_:)``, ``CodedAt(_:)``,
 ``CodedBy(_:)``, ``Default(_:)`` etc.
 

Sources/CodableMacroPlugin/Attributes/Codable/Codable+Expansion.swift

@@ -58,7 +58,8 @@ extension Codable: ConformanceMacro, MemberMacro {
             else { return }
 
             // builder
-            let builder = IgnoreCodingInitialized(from: declaration)
+            let builder = CodingKeys(from: declaration)
+            |> IgnoreCodingInitialized(from: declaration)
             |> KeyPathRegistrationBuilder(
                 provider: CodedAt(from: decl)
                 ?? CodedIn(from: decl)

Sources/CodableMacroPlugin/Attributes/Codable/CodingKeys/CodingKeyTransformer.swift

@@ -0,0 +1,167 @@
+import Foundation
+
+/// A type performing transformation on provided `CodingKey`.
+///
+/// Performs transformation on provided `CodingKey`
+/// based on the strategy passed during initialization.
+/// The separation letter and separated words capitalization
+/// style is adjusted according to the provided case style.
+struct CodingKeyTransformer {
+    /// The key transformation strategy provided.
+    let strategy: CodingKeys.Strategy
+
+    /// Transform provided `CodingKey` string according
+    /// to current strategy.
+    ///
+    /// Adjusts elements in provided `CodingKey` to match
+    /// the current casing strategy.
+    ///
+    /// - Parameter key: The `CodingKey` to transform.
+    /// - Returns: The transformed `CodingKey`.
+    func transform(key: String) -> String {
+        guard !key.isEmpty else { return key }
+
+        let interimKey: String
+        if #available(
+            macOS 13, iOS 16, macCatalyst 16,
+            tvOS 16, watchOS 9, *
+        ) {
+            let regex = #/([a-z0-9])([A-Z])/#
+            interimKey = key.replacing(regex) { match in
+                let (_, first, second) = match.output
+                return "\(first)@\(second)"
+            }.lowercased()
+        } else {
+            let regex = try! NSRegularExpression(pattern: "([a-z0-9])([A-Z])")
+            let range = NSRange(location: 0, length: key.count)
+            interimKey = regex.stringByReplacingMatches(
+                in: key,
+                range: range,
+                withTemplate: "$1@$2"
+            ).lowercased()
+        }
+
+        let parts = interimKey.components(separatedBy: .alphanumerics.inverted)
+        return strategy.capitalization
+            .transform(parts: parts)
+            .joined(separator: strategy.separator)
+    }
+}
+
+fileprivate extension CodingKeys.Strategy {
+    /// The separator being used by current case style.
+    ///
+    /// There might not be any separator for current case style,
+    /// in such case empty string is returned. Otherwise the separator
+    /// character corresponding to current case is returned.
+    var separator: String {
+        switch self {
+        case .camelCase, .PascalCase:
+            return ""
+        case .snake_case, .camel_Snake_Case, .SCREAMING_SNAKE_CASE:
+            return "_"
+        case .kebab－case, .Train－Case, .SCREAMING－KEBAB－CASE:
+            return "-"
+        }
+    }
+}
+
+fileprivate extension CodingKeys.Strategy {
+    /// Represents capitalization style
+    /// of each token in a casing style.
+    ///
+    /// Indicates capitalization style preferred
+    /// by each separated word in a casing style,
+    /// i.e. upper, lower, only first letter is capitalized etc.
+    enum Capitalization {
+        /// Represents all the separated
+        /// words are in upper case.
+        ///
+        /// Typically used for screaming
+        /// style cases with separators.
+        case upper
+        /// Represents all the separated words
+        /// have only first letter capitalized.
+        ///
+        /// Typically used for default
+        /// style cases with separators.
+        case lower
+        /// Represents all the separated
+        /// words are in lower case.
+        ///
+        /// Typically used for default
+        /// style cases with separators.
+        case all
+        /// Represents first word is in lower case
+        /// and subsequent words have only
+        /// first letter capitalized.
+        ///
+        /// Typically used for styles that are variation
+        /// on top of default styles.
+        case exceptFirst
+
+        /// Converts provided string tokens according
+        /// to current casing style.
+        ///
+        /// Adjusts capitalization style of provided string tokens
+        /// according to current casing style.
+        ///
+        /// - Parameter parts: The string tokens to transform.
+        /// - Returns: The transformed string tokens.
+        func transform(parts: [String]) -> [String] {
+            guard !parts.isEmpty else { return parts }
+            switch self {
+            case .upper:
+                return parts.map { $0.uppercased() }
+            case .lower:
+                return parts.map { $0.lowercased() }
+            case .all:
+                return parts.map { $0.uppercasingFirst }
+            case .exceptFirst:
+                let first = parts.first!.lowercasingFirst
+                let rest = parts.dropFirst().map { $0.uppercasingFirst }
+                return [first] + rest
+            }
+        }
+    }
+
+    /// The capitalization casing style of each pattern
+    /// corresponding to current strategy.
+    ///
+    /// Depending on the current style it might be upper,
+    /// lower or capitalizing first word etc.
+    var capitalization: Capitalization {
+        switch self {
+        case .camelCase, .camel_Snake_Case:
+            return .exceptFirst
+        case .snake_case, .kebab－case:
+            return .lower
+        case .SCREAMING_SNAKE_CASE, .SCREAMING－KEBAB－CASE:
+            return .upper
+        case .PascalCase, .Train－Case:
+            return .all
+        }
+    }
+}
+
+/// Helps converting any string to camel case
+///
+/// Picked up from:
+/// https://gist.github.com/reitzig/67b41e75176ddfd432cb09392a270218
+extension String {
+    /// Makes the first letter lowercase.
+    var lowercasingFirst: String { prefix(1).lowercased() + dropFirst() }
+    /// Makes the first letter uppercase.
+    var uppercasingFirst: String { prefix(1).uppercased() + dropFirst() }
+
+    /// Convert any string to camel case
+    ///
+    /// Removes non-alphanumeric characters
+    /// and makes the letters just after these
+    /// characters uppercase.
+    ///
+    /// First letter is made lowercase.
+    var camelCased: String {
+        return CodingKeyTransformer(strategy: .camelCase).transform(key: self)
+    }
+}

Sources/CodableMacroPlugin/Attributes/Codable/CodingKeys/CodingKeys.swift

@@ -0,0 +1,53 @@
+import SwiftSyntax
+
+/// Attribute type for `CodingKeys` macro-attribute.
+///
+/// This type can validate`CodingKeys` macro-attribute
+/// usage and extract data for `Codable` macro to
+/// generate implementation.
+///
+/// Attaching this macro to type declaration indicates all the
+/// property names will be converted to `CodingKey` value
+/// using the strategy provided.
+struct CodingKeys: PeerAttribute {
+    /// The node syntax provided
+    /// during initialization.
+    let node: AttributeSyntax
+
+    /// The key transformation strategy provided.
+    var strategy: Strategy {
+        let expr = node.argument!
+            .as(TupleExprElementListSyntax.self)!.first!.expression
+        return .init(with: expr)
+    }
+
+    /// Creates a new instance with the provided node
+    ///
+    /// The initializer fails to create new instance if the name
+    /// of the provided node is different than this attribute.
+    ///
+    /// - Parameter node: The attribute syntax to create with.
+    /// - Returns: Newly created attribute instance.
+    init?(from node: AttributeSyntax) {
+        guard
+            node.attributeName.as(SimpleTypeIdentifierSyntax.self)!
+                .description == Self.name
+        else { return nil }
+        self.node = node
+    }
+
+    /// Builds diagnoser that can validate this macro
+    /// attached declaration.
+    ///
+    /// Builds diagnoser that validates attached declaration
+    /// has `Codable` macro attached and macro usage
+    /// is not duplicated for the same declaration.
+    ///
+    /// - Returns: The built diagnoser instance.
+    func diagnoser() -> DiagnosticProducer {
+        return AggregatedDiagnosticProducer {
+            mustBeCombined(with: Codable.self)
+            cantDuplicate()
+        }
+    }
+}