feat: added Codable generation macro with

- per field custom key definition
- per field nested key definition
- composition definition per field
- default value definition for decoding failure per field
- memberwise initializer generation with above defaults
- helper decoder/encoder definition per field, i.e. `LossySequenceCoder`

.gitignore

@@ -22,6 +22,16 @@ DerivedData/
 *.perspectivev3
 !default.perspectivev3
 
+# OS generated files #
+######################
+.DS_Store
+.DS_Store?
+._*
+.Spotlight-V100
+.Trashes
+ehthumbs.db
+Thumbs.db
+
 ## Obj-C/Swift specific
 *.hmap
 
@@ -37,14 +47,13 @@ playground.xcworkspace
 # Swift Package Manager
 #
 # Add this line if you want to avoid checking in source code from Swift Package Manager dependencies.
-# Packages/
-# Package.pins
-# Package.resolved
-# *.xcodeproj
-#
+Packages/
+Package.pins
+Package.resolved
+
 # Xcode automatically generates this directory with a .xcworkspacedata file and xcuserdata
 # hence it is not needed unless you have added a package configuration file to your project
-# .swiftpm
+.swiftpm
 
 .build/
 
@@ -54,18 +63,24 @@ playground.xcworkspace
 # you should judge for yourself, the pros and cons are mentioned at:
 # https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
 #
-# Pods/
+Pods/
 #
 # Add this line if you want to avoid checking in source code from the Xcode workspace
-# *.xcworkspace
+*.xcworkspace
 
 # Carthage
 #
 # Add this line if you want to avoid checking in source code from Carthage dependencies.
-# Carthage/Checkouts
+Carthage/Checkouts
 
 Carthage/Build/
 
+# Add Xcode project related files required by Carthage
+DynamicCodableKit.xcodeproj/*
+!DynamicCodableKit.xcodeproj/*.pbxproj
+!DynamicCodableKit.xcodeproj/*.plist
+!DynamicCodableKit.xcodeproj/xcshareddata
+
 # Accio dependency management
 Dependencies/
 .accio/
@@ -88,3 +103,125 @@ fastlane/test_output
 # https://github.com/johnno1962/injectionforxcode
 
 iOSInjectionProject/
+
+# DocC
+.netrc
+.docc-build
+*.doccarchive*
+
+# Built Products
+*.xcframework*
+*.zip
+*.tar*
+
+# Tuist
+Derived/
+
+## Node-Js ignores
+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+
+# Diagnostic reports (https://nodejs.org/api/report.html)
+report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json
+
+# Runtime data
+pids
+*.pid
+*.seed
+*.pid.lock
+
+# Directory for instrumented libs generated by jscoverage/JSCover
+lib-cov
+
+# Coverage directory used by tools like istanbul
+coverage
+*.lcov
+
+# nyc test coverage
+.nyc_output
+
+# Grunt intermediate storage (https://gruntjs.com/creating-plugins#storing-task-files)
+.grunt
+
+# Bower dependency directory (https://bower.io/)
+bower_components
+
+# node-waf configuration
+.lock-wscript
+
+# Compiled binary addons (https://nodejs.org/api/addons.html)
+build/Release
+
+# Dependency directories
+node_modules/
+jspm_packages/
+
+# TypeScript v1 declaration files
+typings/
+
+# TypeScript cache
+*.tsbuildinfo
+
+# Optional npm cache directory
+.npm
+
+# Optional eslint cache
+.eslintcache
+
+# Microbundle cache
+.rpt2_cache/
+.rts2_cache_cjs/
+.rts2_cache_es/
+.rts2_cache_umd/
+
+# Optional REPL history
+.node_repl_history
+
+# Output of 'npm pack'
+*.tgz
+
+# Yarn Integrity file
+.yarn-integrity
+
+# dotenv environment variables file
+.env
+.env.test
+
+# parcel-bundler cache (https://parceljs.org/)
+.cache
+
+# Next.js build output
+.next
+
+# Nuxt.js build / generate output
+.nuxt
+dist
+
+# Gatsby files
+.cache/
+# Comment in the public line in if your project uses Gatsby and *not* Next.js
+# https://nextjs.org/blog/next-9-1#public-directory-support
+# public
+
+# vuepress build output
+.vuepress/dist
+
+# Serverless directories
+.serverless/
+
+# FuseBox cache
+.fusebox/
+
+# DynamoDB Local files
+.dynamodb/
+
+# TernJS port file
+.tern-port
+
+# NPM package lock
+package-lock.json

Package.swift

@@ -0,0 +1,42 @@
+// swift-tools-version: 5.9
+
+import PackageDescription
+import CompilerPluginSupport
+
+let macroDeps: [Target.Dependency] = [
+    .product(name: "SwiftSyntax", package: "swift-syntax"),
+    .product(name: "SwiftSyntaxMacros", package: "swift-syntax"),
+    .product(name: "SwiftOperators", package: "swift-syntax"),
+    .product(name: "SwiftParser", package: "swift-syntax"),
+    .product(name: "SwiftParserDiagnostics", package: "swift-syntax"),
+    .product(name: "SwiftCompilerPlugin", package: "swift-syntax"),
+    .product(name: "OrderedCollections", package: "swift-collections"),
+]
+
+let testDeps: [Target.Dependency] = [
+    "CodableMacroPlugin", "MetaCodable",
+    .product(name: "SwiftSyntaxMacrosTestSupport", package: "swift-syntax"),
+]
+
+let package = Package(
+    name: "MetaCodable",
+    platforms: [
+        .iOS(.v8),
+        .macOS(.v10_15),
+        .tvOS(.v9),
+        .watchOS(.v2),
+        .macCatalyst(.v13),
+    ],
+    products: [
+        .library(name: "MetaCodable", targets: ["MetaCodable"]),
+    ],
+    dependencies: [
+        .package(url: "https://github.com/apple/swift-syntax.git", from: "509.0.0-swift-5.9-DEVELOPMENT-SNAPSHOT-2023-04-25-b"),
+        .package(url: "https://github.com/apple/swift-collections.git", from: "1.0.4"),
+    ],
+    targets: [
+        .macro(name: "CodableMacroPlugin", dependencies: macroDeps),
+        .target(name: "MetaCodable", dependencies: ["CodableMacroPlugin"]),
+        .testTarget(name: "MetaCodableTests", dependencies: testDeps),
+    ]
+)

Sources/CodableMacroPlugin/CodableFieldMacro.swift

@@ -0,0 +1,122 @@
+import SwiftSyntax
+import SwiftDiagnostics
+import SwiftSyntaxMacros
+
+/// Describes a macro that provides metadata to `CodableMacro`
+/// for individual variable decoding approaches.
+///
+/// This macro doesn't perform any expansion rather `CodableMacro`
+/// uses when performing expansion.
+///
+/// This macro verifies that it is attached to only variable declarations and
+/// necessary metadata provided. If not, then this macro generates diagnostic
+/// to remove it.
+struct CodableFieldMacro: PeerMacro {
+    /// The name of macro that allows `CodingKey`
+    /// path customizations
+    static var path: String { "CodablePath" }
+    /// The name of macro that allows
+    /// composition of decoding/encoding
+    static var compose: String { "CodableCompose" }
+
+    /// Argument label used to provide a default value
+    /// in case of decoding failure.
+    static var defaultArgLabel: String { "default" }
+    /// Argument label used to provide a helper instance
+    /// for decoding/encoding customizations or
+    /// custom decoding/encoding implementation.
+    static var helperArgLabel: String { "helper" }
+    /// Collection of all the argument labels.
+    static var argLabels: [String] {
+        return [
+            Self.defaultArgLabel,
+            Self.helperArgLabel,
+        ]
+    }
+
+    /// Provide metadata to `CodableMacro` for final expansion
+    /// and verify proper usage of this macro.
+    ///
+    /// This macro doesn't perform any expansion rather `CodableMacro`
+    /// uses when performing expansion.
+    ///
+    /// This macro verifies that it is attached to only variable declarations
+    /// and necessary metadata provided. If not, then this macro generates
+    /// diagnostic to remove it.
+    ///
+    /// - Parameters:
+    ///   - node: The attribute describing this macro.
+    ///   - declaration: The declaration this macro attribute is attached to.
+    ///   - context: The context in which to perform the macro expansion.
+    ///
+    /// - Returns: No declaration is returned, only attached declaration is
+    ///            analyzed.
+    static func expansion(
+        of node: AttributeSyntax,
+        providingPeersOf declaration: some DeclSyntaxProtocol,
+        in context: some MacroExpansionContext
+    ) throws -> [DeclSyntax] {
+        let name = node.attributeName
+            .as(SimpleTypeIdentifierSyntax.self)!.description
+
+        let (id, msg, severity): (MessageID?, String?, DiagnosticSeverity?) = {
+            if !declaration.is(VariableDeclSyntax.self) {
+                return (
+                    .codableFieldMisuse,
+                    "@\(name) only applicable to variable declarations",
+                    .error
+                )
+            } else if name == Self.path,
+                node.argument?
+                    .as(TupleExprElementListSyntax.self)?.first == nil
+            {
+                return (
+                    .codableFieldUnused,
+                    "Unnecessary use of @\(name) without arguments",
+                    .warning
+                )
+            } else {
+                return (nil, nil, nil)
+            }
+        }()
+
+        guard let id, let msg, let severity else { return [] }
+        context.diagnose(
+            Diagnostic(
+                node: Syntax(node),
+                message: MetaCodableMessage.diagnostic(
+                    message: msg,
+                    id: id,
+                    severity: severity
+                ),
+                fixIts: [
+                    .init(
+                        message: MetaCodableMessage.fixIt(
+                            message: "Remove @\(name) attribute",
+                            id: id
+                        ),
+                        changes: [
+                            .replace(
+                                oldNode: Syntax(node),
+                                newNode: Syntax("" as DeclSyntax)
+                            )
+                        ]
+                    )
+                ]
+            )
+        )
+        return []
+    }
+}
+
+/// An extension that manages `CodableFieldMacro`
+/// specific message ids.
+fileprivate extension MessageID {
+    /// Message id for misuse of `CodableFieldMacro` application.
+    static var codableFieldMisuse: Self { .messageID("codablefield-misuse") }
+    /// Message id for usage of unnecessary `CodableFieldMacro` application.
+    ///
+    /// The `CodableFieldMacro` can be omitted in such scenario
+    /// and the final result will still be the same.
+    static var codableFieldUnused: Self { .messageID("codablepath-unused") }
+}