Type variable with non-trivial upper bound cannot capture 'in' projection

compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/rendering/Renderers.java

@@ -36,6 +36,7 @@ import org.jetbrains.jet.lang.resolve.calls.model.ResolvedCall;
 import org.jetbrains.jet.lang.resolve.name.Name;
 import org.jetbrains.jet.lang.types.*;
 import org.jetbrains.jet.lang.types.checker.JetTypeChecker;
+import org.jetbrains.jet.lang.types.lang.KotlinBuiltIns;
 import org.jetbrains.jet.renderer.DescriptorRenderer;
 import org.jetbrains.jet.renderer.Renderer;
 
@@ -412,10 +413,20 @@ public class Renderers {
             return result;
         }
 
+        String explanation;
+        JetType upperBound = typeParameterWithCapturedConstraint.getUpperBoundsAsType();
+        if (!KotlinBuiltIns.isNullableAny(upperBound)
+            && capturedTypeConstructor.getTypeProjection().getProjectionKind() == Variance.IN_VARIANCE) {
+            explanation = "Type parameter has an upper bound '" + result.getTypeRenderer().render(upperBound) + "'" +
+                           " that cannot be satisfied capturing 'in' projection";
+        }
+        else {
+            explanation = "Only top level type projections can be captured";
+        }
         result.text(newText().normal("'" + typeParameterWithCapturedConstraint.getName() + "'" +
                                      " cannot capture " +
                                      "'" + capturedTypeConstructor.getTypeProjection() + "'. " +
-                                     "Only top level type projections can be captured"));
+                                     explanation));
         return result;
     }
 

compiler/testData/diagnostics/tests/inference/capturedTypes/cannotCaptureInProjection.kt

@@ -0,0 +1,16 @@
+// !DIAGNOSTICS: -UNUSED_VARIABLE -UNUSED_PARAMETER
+// !CHECK_TYPE
+
+fun <T: Any> bar(a: Array<T>): Array<T?> =  null!!
+
+fun test1(a: Array<in Int>) {
+    val r: Array<in Int?> = <!TYPE_INFERENCE_CANNOT_CAPTURE_TYPES!>bar<!>(a)
+    <!TYPE_INFERENCE_CANNOT_CAPTURE_TYPES!>bar<!>(a)
+}
+
+fun <T: Any> foo(l: Array<T>): Array<Array<T?>> = null!!
+
+fun test2(a: Array<in Int>) {
+    val r: Array<out Array<in Int?>> = <!TYPE_INFERENCE_CANNOT_CAPTURE_TYPES!>foo<!>(a)
+    <!TYPE_INFERENCE_CANNOT_CAPTURE_TYPES!>foo<!>(a)
+}

compiler/testData/diagnostics/tests/inference/capturedTypes/cannotCaptureInProjection.txt

@@ -0,0 +1,6 @@
+package
+
+internal fun </*0*/ T : kotlin.Any> bar(/*0*/ a: kotlin.Array<T>): kotlin.Array<T?>
+internal fun </*0*/ T : kotlin.Any> foo(/*0*/ l: kotlin.Array<T>): kotlin.Array<kotlin.Array<T?>>
+internal fun test1(/*0*/ a: kotlin.Array<in kotlin.Int>): kotlin.Unit
+internal fun test2(/*0*/ a: kotlin.Array<in kotlin.Int>): kotlin.Unit

compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java

@@ -5094,6 +5094,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                     JetTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/diagnostics/tests/inference/capturedTypes"), Pattern.compile("^(.+)\\.kt$"), true);
                 }
 
+                @TestMetadata("cannotCaptureInProjection.kt")
+                public void testCannotCaptureInProjection() throws Exception {
+                    String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/inference/capturedTypes/cannotCaptureInProjection.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("captureForNullableTypes.kt")
                 public void testCaptureForNullableTypes() throws Exception {
                     String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/inference/capturedTypes/captureForNullableTypes.kt");