Provide missing arguments when stepping into a function (#10879)

close #10792

Changelog:
- update: replace missing arguments with `Nothing` when schedule a function execution in interactive mode

engine/runtime-instrument-common/src/main/java/org/enso/interpreter/service/ExecutionService.java

@@ -202,7 +202,7 @@ public final class ExecutionService {
 
     Object p = context.getThreadManager().enter();
     try {
-      execute.getCallTarget().call(call);
+      execute.getCallTarget().call(substituteMissingArguments(call));
     } finally {
       context.getThreadManager().leave(p);
       eventNodeFactory.ifPresent(EventBinding::dispose);
@@ -261,6 +261,28 @@ public final class ExecutionService {
         onExecutedVisualizationCallback);
   }
 
+  /**
+   * Replace missing arguments of the provided function call with {@link
+   * org.enso.interpreter.node.expression.builtin.Nothing} to make sure that the function call can
+   * be invoked.
+   *
+   * @param functionCall the function call to update
+   * @return a function call with the updated arguments
+   */
+  private FunctionCallInstrumentationNode.FunctionCall substituteMissingArguments(
+      FunctionCallInstrumentationNode.FunctionCall functionCall) {
+    var arguments = functionCall.getArguments().clone();
+    var argumentInfos = functionCall.getFunction().getSchema().getArgumentInfos();
+    for (var i = 0; i < arguments.length; i++) {
+      if (arguments[i] == null && !argumentInfos[i].hasDefaultValue()) {
+        arguments[i] = context.getBuiltins().nothing();
+      }
+    }
+
+    return new FunctionCallInstrumentationNode.FunctionCall(
+        functionCall.getFunction(), functionCall.getState(), arguments);
+  }
+
   /**
    * Evaluates an expression in the scope of the provided module.
    *

engine/runtime-integration-tests/src/test/scala/org/enso/interpreter/test/instrument/RuntimeServerTest.scala

@@ -489,6 +489,96 @@ class RuntimeServerTest
     )
   }
 
+  it should "substitute Nothing when pushing method with unapplied arguments" in {
+    val contextId  = UUID.randomUUID()
+    val requestId  = UUID.randomUUID()
+    val moduleName = "Enso_Test.Test.Main"
+
+    val metadata         = new Metadata
+    val identityResultId = metadata.addItem(13, 1, "aa")
+    val identityCallId   = metadata.addItem(27, 8, "ab")
+
+    val code =
+      """identity x = x
+        |
+        |main =
+        |    identity
+        |""".stripMargin.linesIterator.mkString("\n")
+    val contents = metadata.appendToCode(code)
+    val mainFile = context.writeMain(contents)
+
+    // create context
+    context.send(Api.Request(requestId, Api.CreateContextRequest(contextId)))
+    context.receive shouldEqual Some(
+      Api.Response(requestId, Api.CreateContextResponse(contextId))
+    )
+
+    // open file
+    context.send(
+      Api.Request(requestId, Api.OpenFileRequest(mainFile, contents))
+    )
+    context.receive shouldEqual Some(
+      Api.Response(Some(requestId), Api.OpenFileResponse)
+    )
+
+    // push main
+    context.send(
+      Api.Request(
+        requestId,
+        Api.PushContextRequest(
+          contextId,
+          Api.StackItem.ExplicitCall(
+            Api.MethodPointer(moduleName, moduleName, "main"),
+            None,
+            Vector()
+          )
+        )
+      )
+    )
+    context.receiveN(3) should contain theSameElementsAs Seq(
+      Api.Response(requestId, Api.PushContextResponse(contextId)),
+      TestMessages.update(
+        contextId,
+        identityCallId,
+        ConstantsGen.FUNCTION_BUILTIN,
+        methodCall = Some(
+          Api.MethodCall(
+            Api.MethodPointer(moduleName, moduleName, "identity"),
+            Vector(0)
+          )
+        ),
+        payload = Api.ExpressionUpdate.Payload.Value(
+          functionSchema = Some(
+            Api.FunctionSchema(
+              Api.MethodPointer(moduleName, moduleName, "identity"),
+              Vector(0)
+            )
+          )
+        )
+      ),
+      context.executionComplete(contextId)
+    )
+    context.consumeOut shouldEqual List()
+
+    // push identity
+    context.send(
+      Api.Request(
+        requestId,
+        Api.PushContextRequest(
+          contextId,
+          Api.StackItem.LocalCall(identityCallId)
+        )
+      )
+    )
+    context.receiveN(3) should contain theSameElementsAs Seq(
+      Api.Response(requestId, Api.PushContextResponse(contextId)),
+      TestMessages
+        .update(contextId, identityResultId, ConstantsGen.NOTHING_BUILTIN),
+      context.executionComplete(contextId)
+    )
+    context.consumeOut shouldEqual List()
+  }
+
   it should "push method with default arguments on top of the stack" in {
     val contextId  = UUID.randomUUID()
     val requestId  = UUID.randomUUID()
@@ -7244,4 +7334,5 @@ class RuntimeServerTest
     )
     context.consumeOut shouldEqual List("Hello World!")
   }
+
 }

engine/runtime/src/main/java/org/enso/interpreter/node/callable/FunctionCallInstrumentationNode.java

@@ -120,7 +120,12 @@ public class FunctionCallInstrumentationNode extends Node implements Instrumenta
     }
 
     /**
-     * @return the arguments passed to the function in this call.
+     * Get the arguments passed to the function in this call.
+     *
+     * <p>The {@code null} value in the arguments array indicates that the corresponding argument
+     * was not provided, and the default value should be used.
+     *
+     * @return the function arguments provided to this call
      */
     public Object[] getArguments() {
       return arguments;