Add a new initializer to GenericConstraint (#63)

* Add a new initializer to SymbolGraph.Symbol.Swift.GenericConstraint that
allows clients to create these structs directly in memory and not only
from decoding JSON.

rdar://112219546

Author: patshaughnessy

Sources/SymbolKit/SymbolGraph/Symbol/Swift/GenericConstraint.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright (c) 2021 Apple Inc. and the Swift project authors
+ Copyright (c) 2021-2023 Apple Inc. and the Swift project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See https://swift.org/LICENSE.txt for license information
@@ -69,13 +69,22 @@ extension SymbolGraph.Symbol.Swift {
          */
         public var rightTypeName: String
 
+        /// Create a new GenericConstraint for the given kind and type names.
+        public init(kind: Kind, leftTypeName: String, rightTypeName: String) {
+            self.kind = kind
+            self.leftTypeName = leftTypeName
+            self.rightTypeName = rightTypeName
+        }
+
+        /// Create a new GenericConstraint by decoding a native format.
         public init(from decoder: Decoder) throws {
             let container = try decoder.container(keyedBy: CodingKeys.self)
             kind = try container.decode(Kind.self, forKey: .kind)
             leftTypeName = try container.decode(String.self, forKey: .leftTypeName)
             rightTypeName = try container.decode(String.self, forKey: .rightTypeName)
         }
 
+        /// Encode a GenericConstraint to a native format.
         public func encode(to encoder: Encoder) throws {
             var container = encoder.container(keyedBy: CodingKeys.self)
             try container.encode(kind, forKey: .kind)

Tests/SymbolKitTests/SymbolGraph/Symbol/Swift/GenericConstraintTests.swift

@@ -0,0 +1,69 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2023 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See https://swift.org/LICENSE.txt for license information
+ See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+*/
+
+import XCTest
+@testable import SymbolKit
+
+class GenericConstraintTests: XCTestCase {
+
+    func testInitializeConformance() throws {
+        let jsonString = """
+        {
+            "kind": "conformance",
+            "lhs": "Self",
+            "rhs": "Hashable",
+        }
+        """
+        let jsonData = Data(jsonString.utf8)
+        let jsonConstraint = try JSONDecoder().decode(SymbolGraph.Symbol.Swift.GenericConstraint.self, from: jsonData)
+        let constraint = SymbolGraph.Symbol.Swift.GenericConstraint(
+            kind: .conformance,
+            leftTypeName: "Self",
+            rightTypeName: "Hashable"
+        )
+        XCTAssertEqual(jsonConstraint, constraint)
+    }
+
+    func testInitializeSuperclass() throws {
+        let jsonString = """
+        {
+            "kind": "superclass",
+            "lhs": "Self",
+            "rhs": "String",
+        }
+        """
+        let jsonData = Data(jsonString.utf8)
+        let jsonConstraint = try JSONDecoder().decode(SymbolGraph.Symbol.Swift.GenericConstraint.self, from: jsonData)
+        let constraint = SymbolGraph.Symbol.Swift.GenericConstraint(
+            kind: .superclass,
+            leftTypeName: "Self",
+            rightTypeName: "String"
+        )
+        XCTAssertEqual(jsonConstraint, constraint)
+    }
+
+    func testInitializeSameType() throws {
+        let jsonString = """
+        {
+            "kind": "sameType",
+            "lhs": "Self",
+            "rhs": "Problem",
+        }
+        """
+        let jsonData = Data(jsonString.utf8)
+        let jsonConstraint = try JSONDecoder().decode(SymbolGraph.Symbol.Swift.GenericConstraint.self, from: jsonData)
+        let constraint = SymbolGraph.Symbol.Swift.GenericConstraint(
+            kind: .sameType,
+            leftTypeName: "Self",
+            rightTypeName: "Problem"
+        )
+        XCTAssertEqual(jsonConstraint, constraint)
+    }
+}