Add support for failing build when multiple types are mapped to the same type

Sources/Java2Swift/JavaToSwift.swift

@@ -267,6 +267,9 @@ struct JavaToSwift: ParsableCommand {
       allClassesToVisit.append(contentsOf: nestedClasses)
     }
 
+    // Validate configurations before writing any files
+    try translator.validateClassConfiguration()
+
     // Translate all of the Java classes into Swift classes.
     for javaClass in javaClasses {
       translator.startNewFile()

Sources/Java2SwiftLib/JavaTranslator+Validation.swift

@@ -0,0 +1,72 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+
+package extension JavaTranslator {
+  struct SwiftTypeName: Hashable {
+    let swiftType: String
+    let swiftModule: String?
+
+    package init(swiftType: String, swiftModule: String?) {
+      self.swiftType = swiftType
+      self.swiftModule = swiftModule
+    }
+  }
+
+  struct SwiftToJavaMapping: Equatable {
+    let swiftType: SwiftTypeName
+    let javaTypes: [String]
+
+    package init(swiftType: SwiftTypeName, javaTypes: [String]) {
+      self.swiftType = swiftType
+      self.javaTypes = javaTypes
+    }
+  }
+
+  enum ValidationError: Error, CustomStringConvertible {
+    case multipleClassesMappedToSameName(swiftToJavaMapping: [SwiftToJavaMapping])
+
+    package var description: String {
+      switch self {
+      case .multipleClassesMappedToSameName(let swiftToJavaMapping):
+              """
+              The following Java classes were mapped to the same Swift type:
+                \(swiftToJavaMapping.map { mapping in
+                  "Swift Type: \(mapping.swiftType.swiftModule ?? "").\(mapping.swiftType.swiftType), Java Types: \(mapping.javaTypes.sorted().joined(separator: ", "))"
+              }.joined(separator: "\n"))
+              """
+      }
+    }
+
+  }
+  func validateClassConfiguration() throws {
+    // Group all classes by swift name
+    let groupedDictionary: [SwiftTypeName: [(String, (String, String?))]] = Dictionary(grouping: translatedClasses, by: { SwiftTypeName(swiftType: $0.value.swiftType, swiftModule: $0.value.swiftModule) })
+    // Find all that are mapped to multiple names
+    let multipleClassesMappedToSameName: [SwiftTypeName: [(String, (String, String?))]] = groupedDictionary.filter { (key: SwiftTypeName, value: [(String, (String, String?))]) in
+      value.count > 1
+    }
+
+    if !multipleClassesMappedToSameName.isEmpty {
+      // Convert them to swift object and throw
+      var errorMappings = [SwiftToJavaMapping]()
+      for (swiftType, swiftJavaMappings) in multipleClassesMappedToSameName {
+        errorMappings.append(SwiftToJavaMapping(swiftType: swiftType, javaTypes: swiftJavaMappings.map(\.0)))
+      }
+      throw ValidationError.multipleClassesMappedToSameName(swiftToJavaMapping: errorMappings)
+    }
+
+  }
+}

Tests/Java2SwiftTests/JavaTranslatorValidationTests.swift

@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Java2SwiftLib
+import XCTest
+
+final class JavaTranslatorValidationTests: XCTestCase {
+  func testValidationError() throws {
+    let translator = try JavaTranslator(swiftModuleName: "SwiftModule", environment: jvm.environment())
+    translator.translatedClasses = [
+      "TestClass": ("Class1", "Module1"),
+      "TestClass2": ("Class1", "Module2"),
+      "TestClass3": ("Class1", "Module1"),
+      "TestClass4": ("Class1", nil)
+    ]
+
+    XCTAssertThrowsError(try translator.validateClassConfiguration()) { error in
+      XCTAssertTrue(error is JavaTranslator.ValidationError)
+      let validationError = error as! JavaTranslator.ValidationError
+      switch validationError {
+      case .multipleClassesMappedToSameName(let swiftToJavaMapping):
+        XCTAssertEqual(swiftToJavaMapping, [
+          JavaTranslator.SwiftToJavaMapping(swiftType: .init(swiftType: "Class1", swiftModule: "Module1"),
+                                            javaTypes: ["TestClass", "TestClass3"])
+        ])
+      }
+    }
+  }
+}