[FE] Fix "Not reachable case" exception

Review: https://jetbrains.team/p/kt/reviews/9967

This commit fixes:

    Cause 2: java.lang.IllegalStateException: Not reachable case. We can always suggest making `open val` property `final`
            at org.jetbrains.kotlin.resolve.DeclarationsChecker.reportMustBeInitialized(DeclarationsChecker.kt:845)
            at org.jetbrains.kotlin.resolve.DeclarationsChecker.checkPropertyInitializer(DeclarationsChecker.kt:778)
            at org.jetbrains.kotlin.resolve.DeclarationsChecker.checkProperty(DeclarationsChecker.kt:614)
            at org.jetbrains.kotlin.resolve.DeclarationsChecker.process(DeclarationsChecker.kt:106)
            at org.jetbrains.kotlin.resolve.BodyResolver.resolveBodies(BodyResolver.java:258)

Reproducible in K1 & K2

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java

@@ -3026,6 +3026,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
                 runTest("compiler/testData/diagnostics/tests/backingField/ValDeferredInitInOpenClassOpenValWarning.kt");
             }
 
+            @Test
+            @TestMetadata("ValWithSetterDeferredInit.kt")
+            public void testValWithSetterDeferredInit() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/backingField/ValWithSetterDeferredInit.kt");
+            }
+
             @Test
             @TestMetadata("VarDeferredInitInFinalClass.kt")
             public void testVarDeferredInitInFinalClass() throws Exception {

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java

@@ -3026,6 +3026,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
                 runTest("compiler/testData/diagnostics/tests/backingField/ValDeferredInitInOpenClassOpenValWarning.kt");
             }
 
+            @Test
+            @TestMetadata("ValWithSetterDeferredInit.kt")
+            public void testValWithSetterDeferredInit() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/backingField/ValWithSetterDeferredInit.kt");
+            }
+
             @Test
             @TestMetadata("VarDeferredInitInFinalClass.kt")
             public void testVarDeferredInitInFinalClass() throws Exception {

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

@@ -3026,6 +3026,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
                 runTest("compiler/testData/diagnostics/tests/backingField/ValDeferredInitInOpenClassOpenValWarning.kt");
             }
 
+            @Test
+            @TestMetadata("ValWithSetterDeferredInit.kt")
+            public void testValWithSetterDeferredInit() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/backingField/ValWithSetterDeferredInit.kt");
+            }
+
             @Test
             @TestMetadata("VarDeferredInitInFinalClass.kt")
             public void testVarDeferredInitInFinalClass() throws Exception {

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

@@ -3032,6 +3032,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
                 runTest("compiler/testData/diagnostics/tests/backingField/ValDeferredInitInOpenClassOpenValWarning.kt");
             }
 
+            @Test
+            @TestMetadata("ValWithSetterDeferredInit.kt")
+            public void testValWithSetterDeferredInit() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/backingField/ValWithSetterDeferredInit.kt");
+            }
+
             @Test
             @TestMetadata("VarDeferredInitInFinalClass.kt")
             public void testVarDeferredInitInFinalClass() throws Exception {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirTopLevelPropertiesChecker.kt

@@ -201,9 +201,6 @@ private fun reportMustBeInitialized(
         suggestMakingItAbstract -> FirErrors.MUST_BE_INITIALIZED_OR_BE_ABSTRACT
         else -> FirErrors.MUST_BE_INITIALIZED
     }
-    if (isOpenValDeferredInitDeprecationWarning && factory == FirErrors.MUST_BE_INITIALIZED) {
-        error("Not reachable case. We can always suggest making `open val` property `final`")
-    }
     reporter.reportOn(
         propertySource,
         when (isMissedMustBeInitializedDeprecationWarning || isOpenValDeferredInitDeprecationWarning) {

compiler/frontend/src/org/jetbrains/kotlin/resolve/DeclarationsChecker.kt

@@ -841,9 +841,6 @@ class DeclarationsChecker(
             suggestMakingItAbstract -> MUST_BE_INITIALIZED_OR_BE_ABSTRACT
             else -> MUST_BE_INITIALIZED
         }
-        if (isOpenValDeferredInitDeprecationWarning && factory == MUST_BE_INITIALIZED) {
-            error("Not reachable case. We can always suggest making `open val` property `final`")
-        }
         trace.report(
             when (isMissedMustBeInitializedDeprecationWarning || isOpenValDeferredInitDeprecationWarning) {
                 true -> factory.deprecationWarning

compiler/testData/diagnostics/tests/backingField/ValWithSetterDeferredInit.kt

@@ -0,0 +1,11 @@
+// FIR_IDENTICAL
+// LANGUAGE: -ProhibitOpenValDeferredInitialization
+// DIAGNOSTICS: -DEBUG_INFO_LEAKING_THIS
+open class A {
+    <!MUST_BE_INITIALIZED_WARNING!>open val c: Int<!>
+        <!VAL_WITH_SETTER!>set(value) {}<!>
+
+    init {
+        c = 1
+    }
+}

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

@@ -3032,6 +3032,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/backingField/ValDeferredInitInOpenClassOpenValWarning.kt");
             }
 
+            @Test
+            @TestMetadata("ValWithSetterDeferredInit.kt")
+            public void testValWithSetterDeferredInit() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/backingField/ValWithSetterDeferredInit.kt");
+            }
+
             @Test
             @TestMetadata("VarDeferredInitInFinalClass.kt")
             public void testVarDeferredInitInFinalClass() throws Exception {