Swift 5.7 support: Replace the AssociatedTypeRequirementsKit package with native casts

Package.resolved

@@ -1,15 +1,6 @@
 {
   "object": {
     "pins": [
-      {
-        "package": "AssociatedTypeRequirementsKit",
-        "repositoryURL": "https://github.com/nerdsupremacist/AssociatedTypeRequirementsKit.git",
-        "state": {
-          "branch": null,
-          "revision": "2e4c49c21ffb2135f1c99fbfcf2119c9d24f5e8c",
-          "version": "0.3.2"
-        }
-      },
       {
         "package": "FineJSON",
         "repositoryURL": "https://github.com/omochi/FineJSON.git",

Package.swift

@@ -21,7 +21,6 @@ let package = Package(
         .library(name: "MetadataSystem", targets: ["MetadataSystem"])
     ],
     dependencies: [
-        .package(url: "https://github.com/nerdsupremacist/AssociatedTypeRequirementsKit.git", .upToNextMinor(from: "0.3.2")),
         .package(url: "https://github.com/apple/swift-collections.git", .upToNextMajor(from: "1.0.0")),
         .package(url: "https://github.com/norio-nomura/XCTAssertCrash.git", from: "0.2.0"),
         .package(url: "https://github.com/omochi/FineJSON.git", from: "1.14.0")
@@ -36,8 +35,7 @@ let package = Package(
         .target(
             name: "MetadataSystem",
             dependencies: [
-                .target(name: "ApodiniContext"),
-                .product(name: "AssociatedTypeRequirementsKit", package: "AssociatedTypeRequirementsKit")
+                .target(name: "ApodiniContext")
             ]
         ),
         .target(

Sources/MetadataSystem/MetadataParser.swift

@@ -7,7 +7,6 @@
 //
 
 import ApodiniContext
-@_implementationOnly import AssociatedTypeRequirementsVisitor
 
 /// An instance of this protocol is used to visit a ``AnyMetadata`` tree.
 public protocol MetadataParser {
@@ -77,14 +76,18 @@ public extension MetadataParser {
 extension MetadataParser {
     // swiftlint:disable:next identifier_name
     func _visit<Definition: MetadataDefinition>(definition: Definition) {
-        if StandardEmptyMetadataVisitor(parser: self)(definition) == nil {
+        if let emptyBlock = definition as? any EmptyMetadata {
+            emptyBlock._accept(parser: self)
+        } else {
             self.visit(definition: definition)
         }
     }
 
     // swiftlint:disable:next identifier_name
     func _visit<Block: AnyMetadataBlock>(block: Block) {
-        if StandardRestrictedMetadataBlockVisitor(parser: self)(block) == nil {
+        if let restrictedBlock = block as? any RestrictedMetadataBlock {
+            restrictedBlock._accept(parser: self)
+        } else {
             self.visit(block: block)
         }
     }
@@ -106,58 +109,15 @@ public struct StandardMetadataParser: MetadataParser {
 }
 
 
-private protocol RestrictedMetadataBlockVisitor: AssociatedTypeRequirementsVisitor {
-    associatedtype Visitor = RestrictedMetadataBlockVisitor
-    associatedtype Input = RestrictedMetadataBlock
-    associatedtype Output
-
-    func callAsFunction<M: RestrictedMetadataBlock>(_ value: M) -> Output
-}
-
-private struct TestBlock: RestrictedMetadataBlock {
-    typealias RestrictedContent = TestBlock
-    var typeErasedContent: AnyMetadata {
-        fatalError("Not implemented!")
-    }
-}
-
-private extension RestrictedMetadataBlockVisitor {
-    @inline(never)
-    @_optimize(none)
-    func _test() {
-        _ = self(TestBlock())
-    }
-}
-
-private struct StandardRestrictedMetadataBlockVisitor: RestrictedMetadataBlockVisitor {
-    var parser: MetadataParser
-    func callAsFunction<M: RestrictedMetadataBlock>(_ value: M) {
-        parser.visit(restrictedBlock: value)
+extension RestrictedMetadataBlock {
+    fileprivate func _accept(parser: MetadataParser) {
+        parser.visit(restrictedBlock: self)
     }
 }
 
 
-private protocol EmptyMetadataVisitor: AssociatedTypeRequirementsVisitor {
-    associatedtype Visitor = EmptyMetadataVisitor
-    associatedtype Input = EmptyMetadata
-    associatedtype Output
-
-    func callAsFunction<M: EmptyMetadata>(_ value: M) -> Output
-}
-
-private struct TestEmpty: EmptyMetadata {}
-
-private extension EmptyMetadataVisitor {
-    @inline(never)
-    @_optimize(none)
-    func _test() {
-        _ = self(TestEmpty())
-    }
-}
-
-private struct StandardEmptyMetadataVisitor: EmptyMetadataVisitor {
-    var parser: MetadataParser
-    func callAsFunction<M: EmptyMetadata>(_ value: M) {
-        parser.visit(empty: value)
+extension EmptyMetadata {
+    fileprivate func _accept(parser: MetadataParser) {
+        parser.visit(empty: self)
     }
 }