Fix incorrect UNINITIALIZED_ENUM_COMPANION diagnostic

#KT-20959 Fixed

compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariablesData.kt

@@ -190,7 +190,10 @@ class PseudocodeVariablesData(val pseudocode: Pseudocode, private val bindingCon
     }
 
     private fun WriteValueInstruction.isTrivialInitializer() =
-            element is KtVariableDeclaration || element is KtParameter
+            // WriteValueInstruction having KtDeclaration as an element means
+            // it must be a write happened at the same time when
+            // the variable (common variable/parameter/object) has been declared
+            element is KtDeclaration
 
     private inner class ReadOnlyInitControlFlowInfoImpl(
             val declaredSet: ImmutableSet<VariableDescriptor>,

compiler/testData/diagnostics/tests/enum/wrongUnitializedEnumCompanion.kt

@@ -0,0 +1,9 @@
+// See KT-20959
+
+enum class Foo {;
+    companion object  {
+        val x = <!DEBUG_INFO_LEAKING_THIS!>foo<!>() // there should be no UNINITIALIZED_ENUM_COMPANION
+
+        private fun foo() = "OK"
+    }
+}

compiler/testData/diagnostics/tests/enum/wrongUnitializedEnumCompanion.txt

@@ -0,0 +1,27 @@
+package
+
+public final enum class Foo : kotlin.Enum<Foo> {
+    private constructor Foo()
+    public final override /*1*/ /*fake_override*/ val name: kotlin.String
+    public final override /*1*/ /*fake_override*/ val ordinal: kotlin.Int
+    protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: Foo): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    protected/*protected and package*/ final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun finalize(): kotlin.Unit
+    public final override /*1*/ /*fake_override*/ /*isHiddenForResolutionEverywhereBesideSupercalls*/ fun getDeclaringClass(): java.lang.Class<Foo!>!
+    public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    public companion object Companion {
+        private constructor Companion()
+        public final val x: kotlin.String
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        private final fun foo(): kotlin.String
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): Foo
+    public final /*synthesized*/ fun values(): kotlin.Array<Foo>
+}

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

@@ -7705,6 +7705,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("wrongUnitializedEnumCompanion.kt")
+            public void testWrongUnitializedEnumCompanion() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/enum/wrongUnitializedEnumCompanion.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("compiler/testData/diagnostics/tests/enum/inner")
             @TestDataPath("$PROJECT_ROOT")
             @RunWith(JUnit3RunnerWithInners.class)

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java

@@ -7705,6 +7705,12 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                 doTest(fileName);
             }
 
+            @TestMetadata("wrongUnitializedEnumCompanion.kt")
+            public void testWrongUnitializedEnumCompanion() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/enum/wrongUnitializedEnumCompanion.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("compiler/testData/diagnostics/tests/enum/inner")
             @TestDataPath("$PROJECT_ROOT")
             @RunWith(JUnit3RunnerWithInners.class)