Builtin methods can support array-like arguments (#7235)

This PR modifies the builtin method processor such that it forbids arrays of non-primitive and non-guest objects in builtin methods. And provides a proper implementation for the builtin methods in `EnsoFile`.

- Remove last `to_array` calls from `File.enso`

build.sbt

@@ -959,6 +959,15 @@ lazy val `interpreter-dsl-test` =
         "-Dgraalvm.locatorDisabled=true",
         s"--upgrade-module-path=${file("engine/runtime/build-cache/truffle-api.jar").absolutePath}"
       ),
+      Test / javacOptions ++= Seq(
+        "-s",
+        (Test / sourceManaged).value.getAbsolutePath
+      ),
+      Compile / logManager :=
+        sbt.internal.util.CustomLogManager.excludeMsg(
+          "Could not determine source for class ",
+          Level.Warn
+        ),
       commands += WithDebugCommand.withDebug,
       libraryDependencies ++= Seq(
         "org.graalvm.truffle" % "truffle-api"           % graalVersion   % "provided",

distribution/lib/Standard/Base/0.0.0-dev/src/System/File.enso

@@ -36,6 +36,7 @@ polyglot java import java.io.OutputStream as Java_Output_Stream
 polyglot java import java.nio.file.FileSystems
 polyglot java import java.nio.file.Path
 polyglot java import java.nio.file.StandardCopyOption
+polyglot java import java.nio.file.StandardOpenOption
 polyglot java import java.time.ZonedDateTime
 polyglot java import org.enso.base.DryRunFileManager
 polyglot java import org.enso.base.encoding.ReportingStreamDecoder
@@ -145,9 +146,9 @@ type File
     with_output_stream self open_options action =
         new_output_stream : File -> Vector File_Access -> Output_Stream ! File_Error
         new_output_stream file open_options =
-            opts = open_options . map (_.to_java) . to_array
+            opts = open_options . map (_.to_java)
             stream = File_Error.handle_java_exceptions file <|
-                file.output_stream_builtin opts.to_array
+                file.output_stream_builtin opts
             ## We re-wrap the File Not Found error to return the parent directory
                instead of the file itself - because the file that is being written
                may not exist and it will not be an error, it is the parent directory
@@ -180,9 +181,10 @@ type File
        `File.with_input_stream` instead, which does resource management.
 
        Arguments:
-       - open_options: A vector of `File_Access` objects determining how to open
-         the stream. These options set the access properties of the stream.
-    input_stream : Vector File_Access -> Input_Stream
+       - open_options: A vector of `StandardOpenOption` polyglot objects
+         determining how to open the stream. These options set the access
+         properties of the stream.
+    input_stream : Vector StandardOpenOption -> Input_Stream
     input_stream self options = @Builtin_Method "File.input_stream"
 
     ## PRIVATE
@@ -564,8 +566,8 @@ type File
             File_Error.handle_java_exceptions self <| case replace_existing of
                 True ->
                   copy_options = [StandardCopyOption.REPLACE_EXISTING]
-                  self.copy_builtin destination copy_options.to_array
-                False -> self.copy_builtin destination [].to_array
+                  self.copy_builtin destination copy_options
+                False -> self.copy_builtin destination []
 
     ## Moves the file to the specified destination.
 
@@ -579,8 +581,8 @@ type File
             File_Error.handle_java_exceptions self <| case replace_existing of
                 True ->
                   copy_options = [StandardCopyOption.REPLACE_EXISTING]
-                  self.move_builtin destination copy_options.to_array
-                False -> self.move_builtin destination [].to_array
+                  self.move_builtin destination copy_options
+                False -> self.move_builtin destination []
 
     ## Deletes the file if it exists on disk.
 
@@ -609,8 +611,8 @@ type File
     new_input_stream : Vector File_Access -> Input_Stream ! File_Error
     new_input_stream self open_options =
         if self.is_directory then Error.throw (File_Error.IO_Error self "File '"+self.path+"' is a directory") else
-            opts = open_options . map (_.to_java) . to_array
-            stream = File_Error.handle_java_exceptions self (self.input_stream opts.to_array)
+            opts = open_options . map (_.to_java)
+            stream = File_Error.handle_java_exceptions self (self.input_stream opts)
             resource = Managed_Resource.register stream close_stream
             Input_Stream.Value self resource
 

engine/runtime/src/main/java/org/enso/interpreter/runtime/data/EnsoFile.java

@@ -4,12 +4,16 @@ import com.oracle.truffle.api.CompilerDirectives;
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.TruffleFile;
 import com.oracle.truffle.api.interop.InteropLibrary;
+import com.oracle.truffle.api.interop.InvalidArrayIndexException;
 import com.oracle.truffle.api.interop.TruffleObject;
+import com.oracle.truffle.api.interop.UnsupportedMessageException;
 import com.oracle.truffle.api.library.CachedLibrary;
 import com.oracle.truffle.api.library.ExportLibrary;
 import com.oracle.truffle.api.library.ExportMessage;
+import java.util.function.IntFunction;
 import org.enso.interpreter.dsl.Builtin;
 import org.enso.interpreter.runtime.EnsoContext;
+import org.enso.interpreter.runtime.error.PanicException;
 import org.enso.interpreter.runtime.library.dispatch.TypesLibrary;
 
 import java.io.IOException;
@@ -45,17 +49,58 @@ public final class EnsoFile implements TruffleObject {
   @Builtin.Method(name = "output_stream_builtin")
   @Builtin.WrapException(from = IOException.class)
   @Builtin.ReturningGuestObject
+  @Builtin.Specialize
   @CompilerDirectives.TruffleBoundary
-  public OutputStream outputStream(OpenOption[] opts) throws IOException {
-    return this.truffleFile.newOutputStream(opts);
+  public OutputStream outputStream(Object opts,
+      EnsoContext ctx,
+      @CachedLibrary(limit = "5") InteropLibrary interop) throws IOException {
+    OpenOption[] openOptions = convertInteropArray(opts, interop, ctx, OpenOption[]::new);
+    return this.truffleFile.newOutputStream(openOptions);
   }
 
   @Builtin.Method
   @Builtin.WrapException(from = IOException.class)
+  @Builtin.Specialize
   @Builtin.ReturningGuestObject
   @CompilerDirectives.TruffleBoundary
-  public InputStream inputStream(OpenOption[] opts) throws IOException {
-    return this.truffleFile.newInputStream(opts);
+  public InputStream inputStream(Object opts,
+      EnsoContext ctx,
+      @CachedLibrary(limit = "5") InteropLibrary interop) throws IOException {
+    OpenOption[] openOptions = convertInteropArray(opts, interop, ctx, OpenOption[]::new);
+    return this.truffleFile.newInputStream(openOptions);
+  }
+
+  @SuppressWarnings("unchecked")
+  private static <T> T[] convertInteropArray(Object arr,
+      InteropLibrary interop,
+      EnsoContext ctx,
+      IntFunction<T[]> hostArrayCtor) {
+    if (!interop.hasArrayElements(arr)) {
+      var vecType = ctx.getBuiltins().vector().getType();
+      var typeError = ctx.getBuiltins().error().makeTypeError(vecType, arr, "opts");
+      throw new PanicException(typeError, interop);
+    }
+    T[] hostArr;
+    try {
+      int size = Math.toIntExact(interop.getArraySize(arr));
+      hostArr = hostArrayCtor.apply(size);
+      for (int i = 0; i < size; i++) {
+        Object elem = interop.readArrayElement(arr, i);
+        if (!ctx.getEnvironment().isHostObject(elem)) {
+          var err = ctx.getBuiltins().error().makeUnsupportedArgumentsError(
+              new Object[]{arr},
+              "Arguments to opts should be host objects from java.io package"
+          );
+          throw new PanicException(err, interop);
+        }
+        hostArr[i] = (T) ctx.getEnvironment().asHostObject(elem);
+      }
+    } catch (UnsupportedMessageException | InvalidArrayIndexException e) {
+      throw new IllegalStateException("Unreachable", e);
+    } catch (ClassCastException e) {
+      throw new PanicException(e, interop);
+    }
+    return hostArr;
   }
 
   @Builtin.Method(name = "read_last_bytes_builtin")
@@ -221,16 +266,24 @@ public final class EnsoFile implements TruffleObject {
 
   @Builtin.Method(name = "copy_builtin", description = "Copy this file to a target destination")
   @Builtin.WrapException(from = IOException.class)
+  @Builtin.Specialize
   @CompilerDirectives.TruffleBoundary
-  public void copy(EnsoFile target, CopyOption[] options) throws IOException {
-    truffleFile.copy(target.truffleFile, options);
+  public void copy(EnsoFile target, Object options,
+      @CachedLibrary(limit = "5") InteropLibrary interop,
+      EnsoContext ctx) throws IOException {
+    CopyOption[] copyOptions = convertInteropArray(options, interop, ctx, CopyOption[]::new);
+    truffleFile.copy(target.truffleFile, copyOptions);
   }
 
   @Builtin.Method(name = "move_builtin", description = "Move this file to a target destination")
   @Builtin.WrapException(from = IOException.class)
+  @Builtin.Specialize
   @CompilerDirectives.TruffleBoundary
-  public void move(EnsoFile target, CopyOption[] options) throws IOException {
-    truffleFile.move(target.truffleFile, options);
+  public void move(EnsoFile target, Object options,
+      @CachedLibrary(limit = "5") InteropLibrary interop,
+      EnsoContext ctx) throws IOException {
+    CopyOption[] copyOptions = convertInteropArray(options, interop, ctx, CopyOption[]::new);
+    truffleFile.move(target.truffleFile, copyOptions);
   }
 
   @Builtin.Method

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/BuiltinsProcessor.java

@@ -178,7 +178,7 @@ public class BuiltinsProcessor extends AbstractProcessor {
                   try {
                     MethodNodeClassGenerator classGenerator =
                         new NoSpecializationClassGenerator(
-                            method, builtinMethodNode, ownerClass, stdLibOwnerClass, i);
+                            processingEnv, method, builtinMethodNode, ownerClass, stdLibOwnerClass, i);
                     classGenerator.generate(
                         processingEnv,
                         methodName,
@@ -232,7 +232,7 @@ public class BuiltinsProcessor extends AbstractProcessor {
           if (encountered.size() == expected) {
             MethodNodeClassGenerator classGenerator =
                 new SpecializationClassGenerator(
-                    encountered, builtinMethodNode, ownerClass, stdLibOwnerClass);
+                    processingEnv, encountered, builtinMethodNode, ownerClass, stdLibOwnerClass);
             classGenerator.generate(
                 processingEnv,
                 builtinMethodName,
@@ -243,7 +243,7 @@ public class BuiltinsProcessor extends AbstractProcessor {
         } else {
           MethodNodeClassGenerator classGenerator =
               new NoSpecializationClassGenerator(
-                  method, builtinMethodNode, ownerClass, stdLibOwnerClass);
+                  processingEnv, method, builtinMethodNode, ownerClass, stdLibOwnerClass);
           classGenerator.generate(
               processingEnv,
               builtinMethodName,

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/MethodProcessor.java

@@ -144,7 +144,6 @@ public class MethodProcessor extends BuiltinsMetadataProcessor<MethodProcessor.M
   private void generateCode(MethodDefinition methodDefinition) throws IOException {
     JavaFileObject gen =
         processingEnv.getFiler().createSourceFile(methodDefinition.getQualifiedName());
-
     Set<String> allImports = new HashSet<>(necessaryImports);
     allImports.addAll(methodDefinition.getImports());
 
@@ -156,6 +155,10 @@ public class MethodProcessor extends BuiltinsMetadataProcessor<MethodProcessor.M
 
       out.println();
 
+      out.println("/**");
+      out.println(" * Generated by {@link " + getClass().getName() + "}.");
+      out.println(" * From {@link " + methodDefinition.getOriginalClassName() + "}.");
+      out.println(" */");
       out.println("@NodeInfo(");
       out.println("  shortName = \"" + methodDefinition.getDeclaredName() + "\",");
       out.println("  description = \"\"\"\n" + methodDefinition.getDescription() + "\"\"\")");
@@ -165,13 +168,13 @@ public class MethodProcessor extends BuiltinsMetadataProcessor<MethodProcessor.M
         out.println("public class " + methodDefinition.getClassName() + " extends BuiltinRootNode implements InlineableNode.Root {");
       }
       out.println("  private @Child " + methodDefinition.getOriginalClassName() + " bodyNode;");
+      out.println();
       out.println("  private static final class Internals {");
       out.println("    Internals(boolean s) {");
       out.println("      this.staticOfInstanceMethod = s;");
       out.println("    }");
-      out.println("    private final boolean staticOfInstanceMethod;");
-
       out.println();
+      out.println("    private final boolean staticOfInstanceMethod;");
 
       for (MethodDefinition.ArgumentDefinition arg : methodDefinition.getArguments()) {
         if (arg.shouldCheckErrors()) {
@@ -278,6 +281,7 @@ public class MethodProcessor extends BuiltinsMetadataProcessor<MethodProcessor.M
           generateWarningsCheck(out, methodDefinition.getArguments(), "arguments");
       for (MethodDefinition.ArgumentDefinition argumentDefinition :
           methodDefinition.getArguments()) {
+        out.println("    /***  Start of processing argument " + argumentDefinition.getPosition() + "  ***/");
         if (argumentDefinition.isImplicit()) {
         } else if (argumentDefinition.isState()) {
           callArgNames.add("state");
@@ -289,6 +293,7 @@ public class MethodProcessor extends BuiltinsMetadataProcessor<MethodProcessor.M
           callArgNames.add(mkArgumentInternalVarName(argumentDefinition));
           generateArgumentRead(out, argumentDefinition, "arguments");
         }
+        out.println("    /***  End of processing argument " + argumentDefinition.getPosition() + "  ***/");
       }
       String executeCall = "bodyNode.execute(" + String.join(", ", callArgNames) + ")";
       if (warningsPossible) {

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/builtins/ExecuteMethodImplGenerator.java

@@ -19,8 +19,12 @@ public final class ExecuteMethodImplGenerator extends MethodGenerator {
   private final boolean needsVarargExpansion;
 
   public ExecuteMethodImplGenerator(
-      ExecutableElement method, boolean convertToGuestValue, int expandedVarargs) {
+      ProcessingEnvironment processingEnvironment,
+      ExecutableElement method,
+      boolean convertToGuestValue,
+      int expandedVarargs) {
     this(
+        processingEnvironment,
         method,
         method.getReturnType().toString(),
         method.getModifiers().contains(Modifier.STATIC),
@@ -31,6 +35,7 @@ public final class ExecuteMethodImplGenerator extends MethodGenerator {
   }
 
   private ExecuteMethodImplGenerator(
+      ProcessingEnvironment processingEnvironment,
       ExecutableElement method,
       String returnTpe,
       boolean isStatic,
@@ -38,7 +43,12 @@ public final class ExecuteMethodImplGenerator extends MethodGenerator {
       boolean convertToGuestValue,
       int expandedVarargs,
       boolean isVarargs) {
-    super(isStatic, isConstructor, convertToGuestValue, TypeWithKind.createFromTpe(returnTpe));
+    super(
+        processingEnvironment,
+        isStatic,
+        isConstructor,
+        convertToGuestValue,
+        TypeWithKind.createFromTpe(returnTpe));
     this.method = method;
     this.varargExpansion = expandedVarargs;
     this.needsVarargExpansion = isVarargs && (varargExpansion > 0);
@@ -112,6 +122,15 @@ public final class ExecuteMethodImplGenerator extends MethodGenerator {
           if (returnTpe.isValidGuestType()) {
             return new String[] {"  return " + qual + "." + name + "(" + paramsApplied + ");"};
           } else {
+            if (!convertToGuestValue) {
+              processingEnvironment
+                  .getMessager()
+                  .printMessage(
+                      javax.tools.Diagnostic.Kind.ERROR,
+                      "Cannot generate method body for "
+                          + method
+                          + " because it returns a host object and convertToGuestValue is false");
+            }
             return new String[] {
               "  return context",
               "      .getEnvironment()",
@@ -134,14 +153,16 @@ public final class ExecuteMethodImplGenerator extends MethodGenerator {
     return result || params.stream().anyMatch(p -> p.needsToHostTranslation());
   }
 
-  public List<String> generate(ProcessingEnvironment processingEnv, String name, String owner) {
-
-    SafeWrapException[] exceptionWrappers = wrapExceptions(processingEnv, method);
+  public List<String> generate(String name, String owner) {
+    SafeWrapException[] exceptionWrappers = wrapExceptions(processingEnvironment, method);
     boolean wrapsExceptions = exceptionWrappers.length != 0;
     List<? extends VariableElement> rawParams = method.getParameters();
     List<MethodParameter> params =
         IntStream.range(0, method.getParameters().size())
-            .mapToObj(i -> fromVariableElementToMethodParameter(i, rawParams.get(i)))
+            .mapToObj(
+                i ->
+                    fromVariableElementToMethodParameter(
+                        processingEnvironment, i, rawParams.get(i)))
             .collect(Collectors.toList());
 
     String[] body = bodyBase(name, owner, params);

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/builtins/MethodGenerator.java

@@ -14,14 +14,16 @@ import javax.annotation.processing.ProcessingEnvironment;
 import javax.lang.model.element.*;
 import javax.lang.model.type.TypeMirror;
 import javax.lang.model.util.Types;
+import javax.tools.Diagnostic.Kind;
 import org.apache.commons.lang3.StringUtils;
 import org.enso.interpreter.dsl.Builtin;
 
 public abstract class MethodGenerator {
   protected final boolean isStatic;
   protected final boolean isConstructor;
-  private final boolean convertToGuestValue;
+  protected final boolean convertToGuestValue;
   protected final TypeWithKind returnTpe;
+  protected final ProcessingEnvironment processingEnvironment;
 
   private static final WrapExceptionExtractor wrapExceptionsExtractor =
       new WrapExceptionExtractor(Builtin.WrapException.class, Builtin.WrapExceptions.class);
@@ -32,18 +34,19 @@ public abstract class MethodGenerator {
   }
 
   public MethodGenerator(
+      ProcessingEnvironment processingEnvironment,
       boolean isStatic,
       boolean isConstructor,
       boolean convertToGuestValue,
       TypeWithKind returnTpe) {
+    this.processingEnvironment = processingEnvironment;
     this.isStatic = isStatic;
     this.isConstructor = isConstructor;
     this.convertToGuestValue = convertToGuestValue;
     this.returnTpe = returnTpe;
   }
 
-  public abstract List<String> generate(
-      ProcessingEnvironment processingEnv, String name, String owner);
+  public abstract List<String> generate(String name, String owner);
 
   /**
    * Generate node's `execute` method definition (return type and necessary parameters). '
@@ -91,10 +94,13 @@ public abstract class MethodGenerator {
             return tpe.baseType();
           } else {
             if (!convertToGuestValue) {
-              throw new RuntimeException(
-                  "If intended, automatic conversion of value of type "
-                      + tpe.baseType()
-                      + " to guest value requires explicit '@Builtin.ReturningGuestObject' annotation");
+              processingEnvironment
+                  .getMessager()
+                  .printMessage(
+                      Kind.ERROR,
+                      "Automatic conversion of value of type "
+                          + tpe.baseType()
+                          + " to guest value requires explicit '@Builtin.ReturningGuestObject' annotation");
             }
             return "Object";
           }
@@ -111,14 +117,28 @@ public abstract class MethodGenerator {
    * @param v variable element representing the parameter
    * @return MethodParameter encapsulating the method's parameter info
    */
-  protected MethodParameter fromVariableElementToMethodParameter(int i, VariableElement v) {
+  protected MethodParameter fromVariableElementToMethodParameter(
+      ProcessingEnvironment processingEnv, int i, VariableElement v) {
     String ensoName =
         CaseFormat.LOWER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, v.getSimpleName().toString());
+    TypeWithKind tpe = TypeWithKind.createFromTpe(v.asType().toString());
+    if (tpe.kind() == TypeKind.ARRAY && !tpe.isValidGuestType()) {
+      processingEnv
+          .getMessager()
+          .printMessage(
+              Kind.ERROR,
+              "Parameter "
+                  + v
+                  + " is an array of host objects, which "
+                  + "is not supported by the MethodGenerator. Either use array of primitive, or valid guest objects, "
+                  + "or accept the array as Object and transform it in the method body.",
+              v);
+    }
     return new MethodParameter(
         i,
         ensoName,
         v.asType().toString(),
-        v.getAnnotationMirrors().stream().map(am -> am.toString()).collect(Collectors.toList()));
+        v.getAnnotationMirrors().stream().map(Object::toString).collect(Collectors.toList()));
   }
 
   protected abstract Optional<Integer> expandVararg(int paramsLen, int paramIndex);

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/builtins/MethodNodeClassGenerator.java

@@ -42,7 +42,6 @@ public abstract class MethodNodeClassGenerator {
       throws IOException {
     JavaFileObject gen =
         processingEnv.getFiler().createSourceFile(builtinNode.jvmFriendlyFullyQualifiedName());
-    ;
     try (PrintWriter out = new PrintWriter(gen.openWriter())) {
       String ensoMethodName = CaseFormat.LOWER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, methodName);
       String ensoTypeName = stdlibOwner.name().replaceAll("([a-z])([A-Z])", "$1_$2");
@@ -60,6 +59,12 @@ public abstract class MethodNodeClassGenerator {
       if (needsFrame != null) {
         moduleOwnerInfo = moduleOwnerInfo + ", needsFrame = " + needsFrame;
       }
+      out.println("/**");
+      out.println(
+          " * Generated by {@link org.enso.interpreter.dsl.builtins.MethodNodeClassGenerator}.");
+      out.println(
+          " * From {@link " + ownerClazz.fullyQualifiedName() + "#" + ownerMethodName + "}.");
+      out.println(" */");
       out.println(
           "@BuiltinMethod(type = \""
               + ensoTypeName
@@ -83,7 +88,7 @@ public abstract class MethodNodeClassGenerator {
         out.println("public class " + builtinNode.jvmFriendlyName() + " extends Node {");
         out.println();
       }
-      for (String line : methodsGen().generate(processingEnv, ownerMethodName, ownerClazz.name())) {
+      for (String line : methodsGen().generate(ownerMethodName, ownerClazz.name())) {
         out.println("  " + line);
       }
       out.println();

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/builtins/NoSpecializationClassGenerator.java

@@ -1,5 +1,6 @@
 package org.enso.interpreter.dsl.builtins;
 
+import javax.annotation.processing.ProcessingEnvironment;
 import javax.lang.model.element.ExecutableElement;
 
 /** Generator for builtin method class with no specialization. */
@@ -7,8 +8,10 @@ public final class NoSpecializationClassGenerator extends MethodNodeClassGenerat
 
   ExecutableElement origin;
   int varArgExpansion;
+  private final ProcessingEnvironment processingEnvironment;
 
   public NoSpecializationClassGenerator(
+      ProcessingEnvironment processingEnvironment,
       ExecutableElement origin,
       ClassName builtinNode,
       ClassName ownerClazz,
@@ -17,20 +20,22 @@ public final class NoSpecializationClassGenerator extends MethodNodeClassGenerat
     super(builtinNode, ownerClazz, stdlibOwner);
     this.origin = origin;
     this.varArgExpansion = varArgExpansion;
+    this.processingEnvironment = processingEnvironment;
   }
 
   public NoSpecializationClassGenerator(
+      ProcessingEnvironment processingEnvironment,
       ExecutableElement origin,
       ClassName builtinNode,
       ClassName ownerClazz,
       ClassName stdlibOwner) {
-    this(origin, builtinNode, ownerClazz, stdlibOwner, 0);
+    this(processingEnvironment, origin, builtinNode, ownerClazz, stdlibOwner, 0);
   }
 
   @Override
   protected MethodGenerator methodsGen() {
     return new ExecuteMethodImplGenerator(
-        origin, needsGuestValueConversion(origin), varArgExpansion);
+        processingEnvironment, origin, needsGuestValueConversion(origin), varArgExpansion);
   }
 
   @Override

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/builtins/SpecializationClassGenerator.java

@@ -1,6 +1,7 @@
 package org.enso.interpreter.dsl.builtins;
 
 import java.util.List;
+import javax.annotation.processing.ProcessingEnvironment;
 import javax.lang.model.element.ExecutableElement;
 
 /**
@@ -10,19 +11,22 @@ import javax.lang.model.element.ExecutableElement;
  */
 public class SpecializationClassGenerator extends MethodNodeClassGenerator {
   List<ExecutableElement> elements;
+  private final ProcessingEnvironment processingEnvironment;
 
   public SpecializationClassGenerator(
+      ProcessingEnvironment processingEnvironment,
       List<ExecutableElement> methodElements,
       ClassName builtinNode,
       ClassName ownerClazz,
       ClassName stdlibOwner) {
     super(builtinNode, ownerClazz, stdlibOwner);
     this.elements = methodElements;
+    this.processingEnvironment = processingEnvironment;
   }
 
   @Override
   protected MethodGenerator methodsGen() {
-    return new SpecializedMethodsGenerator(elements);
+    return new SpecializedMethodsGenerator(processingEnvironment, elements);
   }
 
   @Override

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/builtins/SpecializedMethodsGenerator.java

@@ -13,6 +13,7 @@ import javax.lang.model.element.ElementKind;
 import javax.lang.model.element.ExecutableElement;
 import javax.lang.model.element.Modifier;
 import javax.lang.model.element.VariableElement;
+import javax.tools.Diagnostic;
 import org.apache.commons.lang3.StringUtils;
 import org.enso.interpreter.dsl.AcceptsWarning;
 import org.enso.interpreter.dsl.Builtin;
@@ -23,12 +24,17 @@ public final class SpecializedMethodsGenerator extends MethodGenerator {
   private static final String WithWarningsClassName =
       "org.enso.interpreter.runtime.error.WithWarnings";
 
-  public SpecializedMethodsGenerator(List<ExecutableElement> elements) {
-    this(elements, elements.get(0));
+  public SpecializedMethodsGenerator(
+      ProcessingEnvironment processingEnvironment, List<ExecutableElement> elements) {
+    this(processingEnvironment, elements, elements.get(0));
   }
 
-  private SpecializedMethodsGenerator(List<ExecutableElement> elements, ExecutableElement first) {
+  private SpecializedMethodsGenerator(
+      ProcessingEnvironment processingEnvironment,
+      List<ExecutableElement> elements,
+      ExecutableElement first) {
     this(
+        processingEnvironment,
         elements,
         first.getModifiers().contains(Modifier.STATIC),
         first.getKind() == ElementKind.CONSTRUCTOR,
@@ -45,12 +51,13 @@ public final class SpecializedMethodsGenerator extends MethodGenerator {
   }
 
   public SpecializedMethodsGenerator(
+      ProcessingEnvironment processingEnvironment,
       List<ExecutableElement> elements,
       boolean isStatic,
       boolean isConstructor,
       boolean convertToGuestValue,
       TypeWithKind returnTpe) {
-    super(isStatic, isConstructor, convertToGuestValue, returnTpe);
+    super(processingEnvironment, isStatic, isConstructor, convertToGuestValue, returnTpe);
     this.elements = elements;
   }
 
@@ -59,14 +66,14 @@ public final class SpecializedMethodsGenerator extends MethodGenerator {
   }
 
   @Override
-  public List<String> generate(ProcessingEnvironment processingEnv, String name, String owner) {
-    SpecializationMeta meta = inferExecuteParameters();
+  public List<String> generate(String name, String owner) {
+    SpecializationMeta meta = inferExecuteParameters(processingEnvironment);
     List<String> result = new ArrayList<>();
 
     result.add(methodSigDef(owner, meta.execParams(), true));
     result.add("");
     result.addAll(
-        paramsOfSpecializedMethods(processingEnv, meta.diffParam)
+        paramsOfSpecializedMethods(processingEnvironment, meta.diffParam)
             .flatMap(
                 specializeMethod ->
                     specialize(owner, name, specializeMethod, meta.diffParam).stream())
@@ -98,7 +105,10 @@ public final class SpecializedMethodsGenerator extends MethodGenerator {
                   return new SpecializeMethodInfo(
                       method,
                       IntStream.range(0, params.size())
-                          .mapToObj(i -> fromVariableElementToMethodParameter(i, params.get(i)))
+                          .mapToObj(
+                              i ->
+                                  fromVariableElementToMethodParameter(
+                                      processingEnv, i, params.get(i)))
                           .collect(Collectors.toList()),
                       wrapExceptions(processingEnv, method));
                 });
@@ -132,14 +142,17 @@ public final class SpecializedMethodsGenerator extends MethodGenerator {
     return p.tpe().equals("java.lang.Object") || p.tpe().equals("java.lang.String");
   }
 
-  private SpecializationMeta inferExecuteParameters() {
+  private SpecializationMeta inferExecuteParameters(ProcessingEnvironment processingEnv) {
     Map<Integer, List<MethodParameter>> paramss =
         elements.stream()
             .flatMap(
                 method -> {
                   List<? extends VariableElement> params = method.getParameters();
                   return IntStream.range(0, params.size())
-                      .mapToObj(i -> fromVariableElementToMethodParameter(i, params.get(i)));
+                      .mapToObj(
+                          i ->
+                              fromVariableElementToMethodParameter(
+                                  processingEnv, i, params.get(i)));
                 })
             .collect(Collectors.groupingBy(p -> p.index()));
 
@@ -268,7 +281,24 @@ public final class SpecializedMethodsGenerator extends MethodGenerator {
               "  return new Array((Object[]) " + qual + "." + name + "(" + paramsApplied + "));");
           break;
         default:
-          methodBody.add("  return " + qual + "." + name + "(" + paramsApplied + ");");
+          if (returnTpe.isValidGuestType()) {
+            methodBody.add("  return " + qual + "." + name + "(" + paramsApplied + ");");
+          } else if (convertToGuestValue) {
+            methodBody.add("  var result = " + qual + "." + name + "(" + paramsApplied + ");");
+            methodBody.add("  return EnsoContext.get(this).getEnvironment().asGuestValue(result);");
+          } else {
+            processingEnvironment
+                .getMessager()
+                .printMessage(
+                    Diagnostic.Kind.ERROR,
+                    "Cannot convert return type of "
+                        + owner
+                        + "."
+                        + name
+                        + " to guest value."
+                        + " Specify @ReturningGuestValue annotation",
+                    methodInfo.origin);
+          }
       }
     }