[JExtract/JNI] Omit unsupported types instead of crashing

Samples/JExtractJNISampleApp/Sources/MySwiftLibrary/MySwiftClass.swift

@@ -16,6 +16,7 @@ public class MySwiftClass {
   let x: Int64
   let y: Int64
 
+  public let byte: UInt8 = 0
   public let constant: Int64 = 100
   public var mutable: Int64 = 0
   public var product: Int64 {

Samples/SwiftKitSampleApp/Sources/MySwiftLibrary/MySwiftClass.swift

@@ -14,6 +14,7 @@
 
 public class MySwiftClass {
 
+  public let byte: UInt8 = 0
   public var len: Int
   public var cap: Int
 

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaBindingsPrinting.swift

@@ -176,6 +176,11 @@ extension JNISwift2JavaGenerator {
   }
 
   private func printFunctionBinding(_ printer: inout CodePrinter, _ decl: ImportedFunc) {
+    guard let _ = translatedDecl(for: decl) else {
+      // Failed to translate. Skip.
+      return
+    }
+
     if decl.isStatic || decl.isInitializer || !decl.hasParent {
       printStaticFunctionBinding(&printer, decl)
     } else {
@@ -196,7 +201,7 @@ extension JNISwift2JavaGenerator {
   /// and passes it down to another native function along with the arguments
   /// to call the Swift implementation.
   private func printMemberMethodBindings(_ printer: inout CodePrinter, _ decl: ImportedFunc) {
-    let translatedDecl = translatedDecl(for: decl)
+    let translatedDecl = translatedDecl(for: decl)! // We will only call this method if we can translate the decl.
 
     printDeclDocumentation(&printer, decl)
     printer.printBraceBlock("public \(renderFunctionSignature(decl))") { printer in
@@ -220,7 +225,10 @@ extension JNISwift2JavaGenerator {
   }
 
   private func printInitializerBindings(_ printer: inout CodePrinter, _ decl: ImportedFunc, type: ImportedNominalType) {
-    let translatedDecl = translatedDecl(for: decl)
+    guard let translatedDecl = translatedDecl(for: decl) else {
+      // Failed to translate. Skip.
+      return
+    }
 
     printDeclDocumentation(&printer, decl)
     printer.printBraceBlock("public static \(renderFunctionSignature(decl))") { printer in
@@ -275,7 +283,9 @@ extension JNISwift2JavaGenerator {
   /// `func method(x: Int, y: Int) -> Int` becomes
   /// `long method(long x, long y)`
   private func renderFunctionSignature(_ decl: ImportedFunc) -> String {
-    let translatedDecl = translatedDecl(for: decl)
+    guard let translatedDecl = translatedDecl(for: decl) else {
+      fatalError("Unable to render function signature for a function that cannot be translated: \(decl)")
+    }
     let resultType = translatedDecl.translatedFunctionSignature.resultType
     var parameters = translatedDecl.translatedFunctionSignature.parameters.map(\.asParameter)
 

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+JavaTranslation.swift

@@ -17,13 +17,19 @@ import JavaTypes
 extension JNISwift2JavaGenerator {
   func translatedDecl(
     for decl: ImportedFunc
-  ) -> TranslatedFunctionDecl {
+  ) -> TranslatedFunctionDecl? {
     if let cached = translatedDecls[decl] {
       return cached
     }
 
-    let translation = JavaTranslation(swiftModuleName: self.swiftModuleName)
-    let translated = translation.translate(decl)
+    let translated: TranslatedFunctionDecl?
+    do {
+      let translation = JavaTranslation(swiftModuleName: swiftModuleName)
+      translated = try translation.translate(decl)
+    } catch {
+      self.logger.debug("Failed to translate: '\(decl.swiftDecl.qualifiedNameForDebug)'; \(error)")
+      translated = nil
+    }
 
     translatedDecls[decl] = translated
     return translated
@@ -32,8 +38,8 @@ extension JNISwift2JavaGenerator {
   struct JavaTranslation {
     let swiftModuleName: String
 
-    func translate(_ decl: ImportedFunc) -> TranslatedFunctionDecl {
-      let translatedFunctionSignature = translate(functionSignature: decl.functionSignature)
+    func translate(_ decl: ImportedFunc) throws -> TranslatedFunctionDecl {
+      let translatedFunctionSignature = try translate(functionSignature: decl.functionSignature)
       // Types with no parent will be outputted inside a "module" class.
       let parentName = decl.parentType?.asNominalType?.nominalTypeDecl.qualifiedName ?? swiftModuleName
 
@@ -51,31 +57,31 @@ extension JNISwift2JavaGenerator {
       )
     }
 
-    func translate(functionSignature: SwiftFunctionSignature, isInitializer: Bool = false) -> TranslatedFunctionSignature {
-      let parameters = functionSignature.parameters.enumerated().map { idx, param in
+    func translate(functionSignature: SwiftFunctionSignature, isInitializer: Bool = false) throws -> TranslatedFunctionSignature {
+      let parameters = try functionSignature.parameters.enumerated().map { idx, param in
         let parameterName = param.parameterName ?? "arg\(idx))"
-        return translate(swiftParam: param, parameterName: parameterName)
+        return try translate(swiftParam: param, parameterName: parameterName)
       }
 
-      return TranslatedFunctionSignature(
+      return try TranslatedFunctionSignature(
         parameters: parameters,
         resultType: translate(swiftType: functionSignature.result.type)
       )
     }
 
-    func translate(swiftParam: SwiftParameter, parameterName: String) -> JavaParameter {
-      return JavaParameter(
+    func translate(swiftParam: SwiftParameter, parameterName: String) throws -> JavaParameter {
+      return try JavaParameter(
         name: parameterName,
         type: translate(swiftType: swiftParam.type)
       )
     }
 
-    func translate(swiftType: SwiftType) -> JavaType {
+    func translate(swiftType: SwiftType) throws -> JavaType {
       switch swiftType {
       case .nominal(let nominalType):
         if let knownType = nominalType.nominalTypeDecl.knownTypeKind {
           guard let javaType = translate(knownType: knownType) else {
-            fatalError("unsupported known type: \(knownType)")
+            throw JavaTranslationError.unsupportedSwiftType(swiftType)
           }
           return javaType
         }
@@ -86,7 +92,7 @@ extension JNISwift2JavaGenerator {
         return .void
 
       case .metatype, .optional, .tuple, .function, .existential, .opaque:
-        fatalError("unsupported type: \(self)")
+        throw JavaTranslationError.unsupportedSwiftType(swiftType)
       }
     }
 
@@ -127,4 +133,8 @@ extension JNISwift2JavaGenerator {
     let parameters: [JavaParameter]
     let resultType: JavaType
   }
+
+  enum JavaTranslationError: Error {
+    case unsupportedSwiftType(SwiftType)
+  }
 }

Sources/JExtractSwiftLib/JNI/JNISwift2JavaGenerator+SwiftThunkPrinting.swift

@@ -116,7 +116,11 @@ extension JNISwift2JavaGenerator {
   }
 
   private func printInitializerThunk(_ printer: inout CodePrinter, _ decl: ImportedFunc) {
-    let translatedDecl = translatedDecl(for: decl)
+    guard let translatedDecl = translatedDecl(for: decl) else {
+      // Failed to translate. Skip.
+      return
+    }
+
     let typeName = translatedDecl.parentName
 
     printCDecl(
@@ -146,6 +150,11 @@ extension JNISwift2JavaGenerator {
     _ printer: inout CodePrinter,
     _ decl: ImportedFunc
   ) {
+    guard let _ = translatedDecl(for: decl) else {
+      // Failed to translate. Skip.
+      return
+    }
+
     // Free functions does not have a parent
     if decl.isStatic || !decl.hasParent {
       self.printSwiftStaticFunctionThunk(&printer, decl)
@@ -155,7 +164,7 @@ extension JNISwift2JavaGenerator {
   }
 
   private func printSwiftStaticFunctionThunk(_ printer: inout CodePrinter, _ decl: ImportedFunc) {
-    let translatedDecl = self.translatedDecl(for: decl)
+    let translatedDecl = self.translatedDecl(for: decl)! // We will only call this method if we can translate the decl.
 
     printCDecl(
       &printer,
@@ -172,7 +181,7 @@ extension JNISwift2JavaGenerator {
   }
 
   private func printSwiftMemberFunctionThunk(_ printer: inout CodePrinter, _ decl: ImportedFunc) {
-    let translatedDecl = self.translatedDecl(for: decl)
+    let translatedDecl = self.translatedDecl(for: decl)! // We will only call this method if can translate the decl.
     let swiftParentName = decl.parentType!.asNominalTypeDeclaration!.qualifiedName
 
     printCDecl(
@@ -199,7 +208,9 @@ extension JNISwift2JavaGenerator {
     _ decl: ImportedFunc,
     calleeName: String
   ) {
-    let translatedDecl = self.translatedDecl(for: decl)
+    guard let translatedDecl = self.translatedDecl(for: decl) else {
+      fatalError("Cannot print function downcall for a function that can't be translated: \(decl)")
+    }
     let swiftReturnType = decl.functionSignature.result.type
 
     let tryClause: String = decl.isThrowing ? "try " : ""