Compute return type for property getters more safely

Do not call `isError()` on property's type right after creation of
PropertyGetterDescriptor because the property has no getter yet (it's created
but not yet stored to the property, that happens a bit later), and `isError()`
leads to computation of the delegate type, which for delegated properties
performs some complex resolution (see `VariableTypeResolver#process`) which
relies on the fact that the property already has a getter.

Since the purpose of the original change (883e2e4d) was to support a quick fix
which would add the type to a property in an expression like "val x get() =
...", check the type (or initializer) presence in the PSI instead, this is
safer and is still suitable for the quick fix.

Also fix arguments to "wrong getter type" diagnostic: previously something
useless like "expected Int, actual Int" was reported

 #KT-11809 Fixed

compiler/frontend/src/org/jetbrains/kotlin/resolve/DescriptorResolver.java

@@ -897,16 +897,6 @@ public class DescriptorResolver {
                     annotationSplitter.getAnnotationsForTarget(PROPERTY_GETTER),
                     annotationResolver.resolveAnnotationsWithoutArguments(scopeWithTypeParameters, getter.getModifierList(), trace)));
 
-            KotlinType outType = propertyDescriptor.getType();
-            KotlinType returnType = outType;
-            KtTypeReference returnTypeReference = getter.getReturnTypeReference();
-            if (returnTypeReference != null) {
-                returnType = typeResolver.resolveType(scopeWithTypeParameters, returnTypeReference, trace, true);
-                if (!TypeUtils.equalTypes(returnType, outType)) {
-                    trace.report(WRONG_GETTER_RETURN_TYPE.on(returnTypeReference, propertyDescriptor.getReturnType(), outType));
-                }
-            }
-
             getterDescriptor = new PropertyGetterDescriptorImpl(
                     propertyDescriptor, getterAnnotations,
                     resolveModalityFromModifiers(getter, propertyDescriptor.getModality()),
@@ -914,10 +904,8 @@ public class DescriptorResolver {
                     /* isDefault = */ false, getter.hasModifier(EXTERNAL_KEYWORD),
                     CallableMemberDescriptor.Kind.DECLARATION, null, KotlinSourceElementKt.toSourceElement(getter)
             );
-            if (returnType.isError() && !getter.hasBlockBody() && getter.hasBody()) {
+            KotlinType returnType =
-                returnType = inferReturnTypeFromExpressionBody(storageManager, expressionTypingServices, trace, scopeWithTypeParameters,
+                    determineGetterReturnType(scopeWithTypeParameters, trace, getterDescriptor, getter, propertyDescriptor.getType());
-                                                               DataFlowInfoFactory.EMPTY, getter, getterDescriptor);
-            }
             getterDescriptor.initialize(returnType);
             trace.record(BindingContext.PROPERTY_ACCESSOR, getter, getterDescriptor);
         }
@@ -930,6 +918,37 @@ public class DescriptorResolver {
         return getterDescriptor;
     }
 
+    @NotNull
+    private KotlinType determineGetterReturnType(
+            @NotNull LexicalScope scope,
+            @NotNull BindingTrace trace,
+            @NotNull PropertyGetterDescriptor getterDescriptor,
+            @NotNull KtPropertyAccessor getter,
+            @NotNull KotlinType propertyType
+    ) {
+        KtTypeReference returnTypeReference = getter.getReturnTypeReference();
+        if (returnTypeReference != null) {
+            KotlinType explicitReturnType = typeResolver.resolveType(scope, returnTypeReference, trace, true);
+            if (!TypeUtils.equalTypes(explicitReturnType, propertyType)) {
+                trace.report(WRONG_GETTER_RETURN_TYPE.on(returnTypeReference, propertyType, explicitReturnType));
+            }
+            return explicitReturnType;
+        }
+
+        // If a property has no type specified in the PSI but the getter does (or has an initializer e.g. "val x get() = ..."),
+        // infer the correct type for the getter but leave the error type for the property.
+        // This is useful for an IDE quick fix which would add the type to the property
+        KtProperty property = getter.getProperty();
+        if (!property.hasDelegateExpressionOrInitializer() && property.getTypeReference() == null &&
+            getter.hasBody() && !getter.hasBlockBody()) {
+            return inferReturnTypeFromExpressionBody(
+                    storageManager, expressionTypingServices, trace, scope, DataFlowInfoFactory.EMPTY, getter, getterDescriptor
+            );
+        }
+
+        return propertyType;
+    }
+
     @NotNull
     /*package*/ static DeferredType inferReturnTypeFromExpressionBody(
             @NotNull StorageManager storageManager,

compiler/testData/diagnostics/tests/delegatedProperty/nonDefaultAccessors.kt

@@ -0,0 +1,12 @@
+// KT-11809 Assertion error when delegated property has getter
+
+class A {
+    val p1 by this
+        get
+
+    var p2 by this
+        <!ACCESSOR_FOR_DELEGATED_PROPERTY!>get() = ""<!>
+
+    operator fun getValue(a: Any?, p: Any?) = ""
+    operator fun setValue(a: Any?, p: Any?, v: Any?) {}
+}

compiler/testData/diagnostics/tests/delegatedProperty/nonDefaultAccessors.txt

@@ -0,0 +1,12 @@
+package
+
+public final class A {
+    public constructor A()
+    public final val p1: kotlin.String
+    public final var p2: kotlin.String
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public final operator fun getValue(/*0*/ a: kotlin.Any?, /*1*/ p: kotlin.Any?): kotlin.String
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final operator fun setValue(/*0*/ a: kotlin.Any?, /*1*/ p: kotlin.Any?, /*2*/ v: kotlin.Any?): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/regressions/kt251.kt

@@ -5,7 +5,7 @@ class A() {
             field = <!TYPE_MISMATCH!>value<!>
         }
     val y: Int
-        get(): <!WRONG_GETTER_RETURN_TYPE!>String<!> = "s"
+        get(): <!WRONG_GETTER_RETURN_TYPE(Int; String)!>String<!> = "s"
     val z: Int
         get() {
             return <!TYPE_MISMATCH!>"s"<!>

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -4767,6 +4767,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("nonDefaultAccessors.kt")
+            public void testNonDefaultAccessors() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/delegatedProperty/nonDefaultAccessors.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("propertyDefferedType.kt")
             public void testPropertyDefferedType() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/delegatedProperty/propertyDefferedType.kt");