K2: Propagate explicit getter type to the property without initializer

In K1, we have the rules like:
- if there's explicit type of a property, then use it
- if there's an initializer, obtain its expression-type
- Otherwise, use getter's return type

The case when getter's type is implicit is handled at
FirDeclarationsResolveTransformer.transformProperty

^KT-56707 Fixed

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java

@@ -25056,12 +25056,24 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                 runTest("compiler/testData/diagnostics/tests/properties/extensionPropertyMustHaveAccessorsOrBeAbstract.kt");
             }
 
+            @Test
+            @TestMetadata("inferPropertyTypeFromGetter.kt")
+            public void testInferPropertyTypeFromGetter() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/properties/inferPropertyTypeFromGetter.kt");
+            }
+
             @Test
             @TestMetadata("kt47621.kt")
             public void testKt47621() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/properties/kt47621.kt");
             }
 
+            @Test
+            @TestMetadata("kt56707.kt")
+            public void testKt56707() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/properties/kt56707.kt");
+            }
+
             @Test
             @TestMetadata("lateinitOnTopLevel.kt")
             public void testLateinitOnTopLevel() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java

@@ -25062,12 +25062,24 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/properties/extensionPropertyMustHaveAccessorsOrBeAbstract.kt");
             }
 
+            @Test
+            @TestMetadata("inferPropertyTypeFromGetter.kt")
+            public void testInferPropertyTypeFromGetter() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/properties/inferPropertyTypeFromGetter.kt");
+            }
+
             @Test
             @TestMetadata("kt47621.kt")
             public void testKt47621() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/properties/kt47621.kt");
             }
 
+            @Test
+            @TestMetadata("kt56707.kt")
+            public void testKt56707() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/properties/kt56707.kt");
+            }
+
             @Test
             @TestMetadata("lateinitOnTopLevel.kt")
             public void testLateinitOnTopLevel() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java

@@ -25056,12 +25056,24 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/tests/properties/extensionPropertyMustHaveAccessorsOrBeAbstract.kt");
             }
 
+            @Test
+            @TestMetadata("inferPropertyTypeFromGetter.kt")
+            public void testInferPropertyTypeFromGetter() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/properties/inferPropertyTypeFromGetter.kt");
+            }
+
             @Test
             @TestMetadata("kt47621.kt")
             public void testKt47621() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/properties/kt47621.kt");
             }
 
+            @Test
+            @TestMetadata("kt56707.kt")
+            public void testKt56707() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/properties/kt56707.kt");
+            }
+
             @Test
             @TestMetadata("lateinitOnTopLevel.kt")
             public void testLateinitOnTopLevel() throws Exception {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirTypeResolveTransformer.kt

@@ -6,7 +6,9 @@
 package org.jetbrains.kotlin.fir.resolve.transformers
 
 import kotlinx.collections.immutable.toImmutableList
+import org.jetbrains.kotlin.KtFakeSourceElementKind
 import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.copyWithNewSourceKind
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.isFromVararg
 import org.jetbrains.kotlin.fir.expressions.*
@@ -154,8 +156,16 @@ open class FirTypeResolveTransformer(
                     setAccessorTypesByPropertyType(property)
                 }
 
-                if (property.returnTypeRef is FirResolvedTypeRef && property.delegate != null) {
+                when {
-                    setAccessorTypesByPropertyType(property)
+                    property.returnTypeRef is FirResolvedTypeRef && property.delegate != null -> {
+                        setAccessorTypesByPropertyType(property)
+                    }
+                    property.returnTypeRef !is FirResolvedTypeRef && property.initializer == null &&
+                            property.getter?.returnTypeRef is FirResolvedTypeRef -> {
+                        property.replaceReturnTypeRef(
+                            property.getter!!.returnTypeRef.copyWithNewSourceKind(KtFakeSourceElementKind.PropertyTypeFromGetterReturnType)
+                        )
+                    }
                 }
 
                 unboundCyclesInTypeParametersSupertypes(property)

compiler/frontend.common/src/org/jetbrains/kotlin/KtSourceElement.kt

@@ -262,6 +262,9 @@ sealed class KtFakeSourceElementKind(final override val shouldSkipErrorTypeRepor
 
     // Synthetic calls for if/when/try/etc.
     object SyntheticCall : KtFakeSourceElementKind()
+
+    // When property doesn't have an initializer and explicit return type, but its getter's return type is specified
+    object PropertyTypeFromGetterReturnType : KtFakeSourceElementKind()
 }
 
 sealed class AbstractKtSourceElement {

compiler/testData/diagnostics/tests/properties/inferPropertyTypeFromGetter.kt

@@ -0,0 +1,19 @@
+// FIR_IDENTICAL
+// ISSUE: KT-56707
+
+class Foo0 {
+    val child = 1
+    val allChildren
+        get(): Int = child + allChildren // Should not be TYPECHECKER_HAS_RUN_INTO_RECURSIVE_PROBLEM on `allChildren` reference
+}
+
+class Foo1 {
+    val child = 1
+    val allChildren
+        get() = child + 1
+}
+
+fun use() {
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Int")!>Foo0().allChildren<!>
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Int")!>Foo1().allChildren<!>
+}

compiler/testData/diagnostics/tests/properties/inferenceFromGetters/explicitGetterType.fir.kt

@@ -1,18 +0,0 @@
-// !CHECK_TYPE
-val x get(): String = foo()
-val y get(): List<Int> = bar()
-val z get(): List<Int> {
-    return bar()
-}
-
-val u get(): String = <!UNRESOLVED_REFERENCE!>field<!>
-
-fun <E> foo(): E = null!!
-fun <E> bar(): List<E> = null!!
-
-
-fun baz() {
-    x checkType { _<String>() }
-    y checkType { _<List<Int>>() }
-    z checkType { _<List<Int>>() }
-}

compiler/testData/diagnostics/tests/properties/inferenceFromGetters/explicitGetterType.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !CHECK_TYPE
 val x get(): String = foo()
 val y get(): List<Int> = bar()

compiler/testData/diagnostics/tests/properties/kt56707.kt

@@ -0,0 +1,13 @@
+// FIR_IDENTICAL
+// WITH_STDLIB
+// ISSUE: KT-56707
+
+class Foo {
+    val children = mutableSetOf<Foo>()
+    val allChildren
+        get() : Set<Foo> = (children + children.flatMap { it.allChildren }).toSet() // Should not be TYPECHECKER_HAS_RUN_INTO_RECURSIVE_PROBLEM on `allChildren` reference
+}
+
+fun use() {
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.collections.Set<Foo>")!>Foo().allChildren<!>
+}

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -25062,12 +25062,24 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/properties/extensionPropertyMustHaveAccessorsOrBeAbstract.kt");
             }
 
+            @Test
+            @TestMetadata("inferPropertyTypeFromGetter.kt")
+            public void testInferPropertyTypeFromGetter() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/properties/inferPropertyTypeFromGetter.kt");
+            }
+
             @Test
             @TestMetadata("kt47621.kt")
             public void testKt47621() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/properties/kt47621.kt");
             }
 
+            @Test
+            @TestMetadata("kt56707.kt")
+            public void testKt56707() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/properties/kt56707.kt");
+            }
+
             @Test
             @TestMetadata("lateinitOnTopLevel.kt")
             public void testLateinitOnTopLevel() throws Exception {