Fixed rendering of error message for 'cannot capture type' error

Type variable should be chosen correctly

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/Renderers.java

@@ -394,18 +394,26 @@ public class Renderers {
             @NotNull InferenceErrorData inferenceErrorData,
             @NotNull TabledDescriptorRenderer result
     ) {
-        ConstraintSystem constraintSystem = inferenceErrorData.constraintSystem;
+        ConstraintSystemImpl constraintSystem = (ConstraintSystemImpl) inferenceErrorData.constraintSystem;
+        List<ConstraintError> errors = constraintSystem.getConstraintErrors();
         TypeParameterDescriptor typeParameterWithCapturedConstraint = null;
+        for (ConstraintError error : errors) {
+            if (error instanceof CannotCapture) {
+                typeParameterWithCapturedConstraint = ((CannotCapture) error).getTypeVariable();
+            }
+        }
+        if (typeParameterWithCapturedConstraint == null) {
+            LOG.error(renderDebugMessage("An error 'cannot capture type parameter' is not found in errors", inferenceErrorData));
+            return result;
+        }
+
         CapturedTypeConstructor capturedTypeConstructor = null;
-        for (TypeParameterDescriptor typeParameter : constraintSystem.getTypeVariables()) {
+        TypeBounds typeBounds = constraintSystem.getTypeBounds(typeParameterWithCapturedConstraint);
-            TypeBounds typeBounds = constraintSystem.getTypeBounds(typeParameter);
             for (TypeBounds.Bound bound : typeBounds.getBounds()) {
                 TypeConstructor constructor = bound.getConstrainingType().getConstructor();
                 if (constructor instanceof CapturedTypeConstructor) {
-                    typeParameterWithCapturedConstraint = typeParameter;
                     capturedTypeConstructor = (CapturedTypeConstructor) constructor;
                 }
-            }
         }
         if (capturedTypeConstructor == null) {
             LOG.error(renderDebugMessage("There is no captured type in bounds, but there is an error 'cannot capture type parameter'",

core/descriptors/src/org/jetbrains/kotlin/resolve/calls/inference/ConstraintError.kt

@@ -26,3 +26,6 @@ class TypeConstructorMismatch(constraintPosition: ConstraintPosition): Constrain
 class ErrorInConstrainingType(constraintPosition: ConstraintPosition): ConstraintError(constraintPosition)
 
 class CannotCapture(constraintPosition: ConstraintPosition, val typeVariable: TypeParameterDescriptor): ConstraintError(constraintPosition)
+
+fun ConstraintError.substituteTypeVariable(substitution: (TypeParameterDescriptor) -> TypeParameterDescriptor) =
+        if (this is CannotCapture) CannotCapture(constraintPosition, substitution(typeVariable)) else this

core/descriptors/src/org/jetbrains/kotlin/resolve/calls/inference/ConstraintSystemImpl.kt

@@ -51,7 +51,10 @@ public class ConstraintSystemImpl : ConstraintSystem {
     }
 
     private val typeParameterBounds = LinkedHashMap<TypeParameterDescriptor, TypeBoundsImpl>()
+
     private val errors = ArrayList<ConstraintError>()
+    public val constraintErrors: List<ConstraintError>
+        get() = errors
 
     private val constraintSystemStatus = object : ConstraintSystemStatus {
         // for debug ConstraintsUtil.getDebugMessageForStatus might be used
@@ -134,7 +137,7 @@ public class ConstraintSystemImpl : ConstraintSystem {
 
     public fun copy(): ConstraintSystem = createNewConstraintSystemFromThis({ it }, { it.copy() }, { true })
 
-    public fun substituteTypeVariables(typeVariablesMap: (TypeParameterDescriptor) -> TypeParameterDescriptor?): ConstraintSystem {
+    public fun substituteTypeVariables(typeVariablesMap: (TypeParameterDescriptor) -> TypeParameterDescriptor): ConstraintSystem {
         // type bounds are proper types and don't contain other variables
         return createNewConstraintSystemFromThis(typeVariablesMap, { it }, { true })
     }
@@ -163,16 +166,16 @@ public class ConstraintSystemImpl : ConstraintSystem {
     }
 
     private fun createNewConstraintSystemFromThis(
-            substituteTypeVariable: (TypeParameterDescriptor) -> TypeParameterDescriptor?,
+            substituteTypeVariable: (TypeParameterDescriptor) -> TypeParameterDescriptor,
             replaceTypeBounds: (TypeBoundsImpl) -> TypeBoundsImpl,
             filterConstraintPosition: (ConstraintPosition) -> Boolean
     ): ConstraintSystem {
         val newSystem = ConstraintSystemImpl()
         for ((typeParameter, typeBounds) in typeParameterBounds) {
             val newTypeParameter = substituteTypeVariable(typeParameter)
-            newSystem.typeParameterBounds.put(newTypeParameter!!, replaceTypeBounds(typeBounds))
+            newSystem.typeParameterBounds.put(newTypeParameter, replaceTypeBounds(typeBounds))
         }
-        newSystem.errors.addAll(errors.filter { filterConstraintPosition(it.constraintPosition) })
+        newSystem.errors.addAll(errors.filter { filterConstraintPosition(it.constraintPosition) }.map { it.substituteTypeVariable(substituteTypeVariable) })
         return newSystem
     }
 
@@ -188,11 +191,12 @@ public class ConstraintSystemImpl : ConstraintSystem {
 
     private fun addConstraint(constraintKind: ConstraintKind, subType: JetType?, superType: JetType?, constraintPosition: ConstraintPosition) {
         val typeCheckingProcedure = TypeCheckingProcedure(object : TypeCheckingProcedureCallbacks {
-            private var isTopLevel = true
+            private var depth = 0
 
             override fun assertEqualTypes(a: JetType, b: JetType, typeCheckingProcedure: TypeCheckingProcedure): Boolean {
-                isTopLevel = false
+                depth++
                 doAddConstraint(EQUAL, a, b, constraintPosition, typeCheckingProcedure)
+                depth--
                 return true
 
             }
@@ -202,15 +206,16 @@ public class ConstraintSystemImpl : ConstraintSystem {
             }
 
             override fun assertSubtype(subtype: JetType, supertype: JetType, typeCheckingProcedure: TypeCheckingProcedure): Boolean {
-                isTopLevel = false
+                depth++
                 doAddConstraint(SUB_TYPE, subtype, supertype, constraintPosition, typeCheckingProcedure)
+                depth--
                 return true
             }
 
             override fun capture(typeVariable: JetType, typeProjection: TypeProjection): Boolean {
                 val myTypeVariable = getMyTypeVariable(typeVariable)
                 if (myTypeVariable != null && constraintPosition.isCaptureAllowed()) {
-                    if (!isTopLevel) {
+                    if (depth > 0) {
                         errors.add(CannotCapture(constraintPosition, myTypeVariable))
                     }
                     generateTypeParameterCaptureConstraint(typeVariable, typeProjection, constraintPosition)

idea/testData/diagnosticMessage/typeInferenceCannotCaptureTypes.kt

@@ -0,0 +1,10 @@
+// !DIAGNOSTICS_NUMBER: 1
+// !DIAGNOSTICS: TYPE_INFERENCE_CANNOT_CAPTURE_TYPES
+
+class My<R, T>
+
+fun <R, T> foo(my: My<Array<R>, T>): My<Array<R>, T> = my
+
+fun test11(my: My<Array<out Int>, out Int>) {
+    foo(my)
+}

idea/testData/diagnosticMessage/typeInferenceCannotCaptureTypes1.txt

@@ -0,0 +1,2 @@
+<!-- typeInferenceCannotCaptureTypes1 -->
+Type inference failed: 'R' cannot capture 'out Int'. Only top-level type projections can be captured

idea/tests/org/jetbrains/kotlin/idea/highlighter/DiagnosticMessageTestGenerated.java

@@ -150,6 +150,12 @@ public class DiagnosticMessageTestGenerated extends AbstractDiagnosticMessageTes
         doTest(fileName);
     }
 
+    @TestMetadata("typeInferenceCannotCaptureTypes.kt")
+    public void testTypeInferenceCannotCaptureTypes() throws Exception {
+        String fileName = JetTestUtils.navigationMetadata("idea/testData/diagnosticMessage/typeInferenceCannotCaptureTypes.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("typeInferenceExpectedTypeMismatch.kt")
     public void testTypeInferenceExpectedTypeMismatch() throws Exception {
         String fileName = JetTestUtils.navigationMetadata("idea/testData/diagnosticMessage/typeInferenceExpectedTypeMismatch.kt");