Add checks for const modifier applicability

1. Must be initialized in-place
2. Can not be open/abstract
3. Can not be an override
4. Can not be delegated
5. Initializer must be a compile-time constant
6. No getters
7. `const` is not applicable to vars or locals
8. `const val` should be whether top-level property or object member

compiler/testData/diagnostics/tests/modifiers/IllegalModifiers.kt

@@ -36,6 +36,7 @@ class IllegalModifiers1(
         <!WRONG_MODIFIER_TARGET!>reified<!>
         <!WRONG_MODIFIER_TARGET!>enum<!>
         <!WRONG_MODIFIER_TARGET!>private<!>
+        <!WRONG_MODIFIER_TARGET!>const<!>
         <!UNUSED_PARAMETER!>a<!>: Int)
 
 //Check multiple illegal modifiers in constructor
@@ -110,6 +111,7 @@ class IllegalModifiers7() {
     <!INCOMPATIBLE_MODIFIERS!>in<!>
     <!WRONG_MODIFIER_TARGET!>vararg<!>
     <!WRONG_MODIFIER_TARGET!>reified<!>
+    <!WRONG_MODIFIER_TARGET!>const<!>
     fun foo() {}
 }
 
@@ -126,6 +128,7 @@ class IllegalModifiers8 {
     <!INCOMPATIBLE_MODIFIERS!>final<!>
     <!WRONG_MODIFIER_TARGET!>vararg<!>
     <!WRONG_MODIFIER_TARGET!>reified<!>
+    <!INCOMPATIBLE_MODIFIERS!>const<!>
     constructor() {}
 
     constructor(<!WRONG_MODIFIER_TARGET!>private<!> <!WRONG_MODIFIER_TARGET!>enum<!> <!WRONG_MODIFIER_TARGET!>abstract<!> <!UNUSED_PARAMETER!>x<!>: Int) {}
@@ -149,6 +152,7 @@ class IllegalModifiers10
 <!INCOMPATIBLE_MODIFIERS!>in<!>
 <!INCOMPATIBLE_MODIFIERS!>final<!>
 <!WRONG_MODIFIER_TARGET!>vararg<!>
-<!WRONG_MODIFIER_TARGET!>reified<!> constructor()
+<!WRONG_MODIFIER_TARGET!>reified<!>
+<!INCOMPATIBLE_MODIFIERS!>const<!> constructor()
 
 class IllegalModifiers11 <!INCOMPATIBLE_MODIFIERS!>private<!> <!INCOMPATIBLE_MODIFIERS!>protected<!> constructor()

compiler/testData/diagnostics/tests/modifiers/const/applicability.kt

@@ -0,0 +1,75 @@
+// !DIAGNOSTICS:-UNUSED_VARIABLE
+
+const val topLevel: Int = 0
+const val topLevelInferred = 1
+<!WRONG_MODIFIER_TARGET!>const<!> var topLeveLVar: Int = 2
+
+private val privateTopLevel = 3
+
+object A {
+    const val inObject: Int = 4
+}
+
+class B(<!CONST_VAL_NOT_TOP_LEVEL_OR_OBJECT!>const<!> val constructor: Int = 5)
+
+abstract class C {
+    <!INCOMPATIBLE_MODIFIERS!>open<!> <!CONST_VAL_NOT_TOP_LEVEL_OR_OBJECT, INCOMPATIBLE_MODIFIERS!>const<!> val x: Int = 6
+
+    <!INCOMPATIBLE_MODIFIERS!>abstract<!> <!CONST_VAL_NOT_TOP_LEVEL_OR_OBJECT, INCOMPATIBLE_MODIFIERS!>const<!> val y: Int = <!ABSTRACT_PROPERTY_WITH_INITIALIZER!>7<!>
+
+    companion object {
+        const val inCompaionObject = 8
+    }
+}
+
+<!ABSTRACT_MEMBER_NOT_IMPLEMENTED!>object D<!> : C() {
+    <!INCOMPATIBLE_MODIFIERS!>override<!> <!INCOMPATIBLE_MODIFIERS!>const<!> val x: Int = 9
+
+    const val inObject = 10
+
+    final const val final = 11
+
+    <!CONST_VAL_WITHOUT_INITIALIZER!>const<!> val withoutInitializer: Int
+
+    init {
+        withoutInitializer = 12
+    }
+}
+
+const val delegated: Int <!CONST_VAL_WITH_DELEGATE!>by Delegate()<!>
+
+
+const val withGetter: Int
+<!CONST_VAL_WITH_GETTER!>get() = 13<!>
+
+fun foo(): Int {
+    <!WRONG_MODIFIER_TARGET!>const<!> val local: Int = 14
+    return 15
+}
+
+enum class MyEnum {
+    A {
+        <!CONST_VAL_NOT_TOP_LEVEL_OR_OBJECT!>const<!> val inEnumEntry = 16
+    };
+    <!CONST_VAL_NOT_TOP_LEVEL_OR_OBJECT!>const<!> val inEnum = 17
+}
+
+class Outer {
+    inner class Inner {
+        object C {
+            const val a = 18
+        }
+    }
+}
+
+const val defaultGetter = 19
+    <!CONST_VAL_WITH_GETTER!>get<!>
+
+const val nonConstInitializer = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>foo()<!>
+
+// ------------------
+class Delegate {
+    fun get(thisRef: Any?, prop: PropertyMetadata): Int = 1
+
+    fun set(thisRef: Any?, prop: PropertyMetadata, value: Int) = Unit
+}

compiler/testData/diagnostics/tests/modifiers/const/applicability.txt

@@ -0,0 +1,105 @@
+package
+
+public const val defaultGetter: kotlin.Int = 19
+public const val delegated: kotlin.Int
+public const val nonConstInitializer: kotlin.Int
+private val privateTopLevel: kotlin.Int = 3
+public const var topLeveLVar: kotlin.Int
+public const val topLevel: kotlin.Int = 0
+public const val topLevelInferred: kotlin.Int = 1
+public const val withGetter: kotlin.Int
+public fun foo(): kotlin.Int
+
+public object A {
+    private constructor A()
+    public const final val inObject: kotlin.Int = 4
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class B {
+    public constructor B(/*0*/ constructor: kotlin.Int = ...)
+    public final val constructor: kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class C {
+    public constructor C()
+    public const open val x: kotlin.Int = 6
+    public const abstract val y: kotlin.Int = 7
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open 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 const final val inCompaionObject: kotlin.Int = 8
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}
+
+public object D : C {
+    private constructor D()
+    public const final val final: kotlin.Int = 11
+    public const final val inObject: kotlin.Int = 10
+    public const final val withoutInitializer: kotlin.Int
+    public const open override /*1*/ val x: kotlin.Int = 9
+    public const abstract override /*1*/ /*fake_override*/ val y: kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class Delegate {
+    public constructor Delegate()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public final fun get(/*0*/ thisRef: kotlin.Any?, /*1*/ prop: kotlin.PropertyMetadata): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final fun set(/*0*/ thisRef: kotlin.Any?, /*1*/ prop: kotlin.PropertyMetadata, /*2*/ value: kotlin.Int): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final enum class MyEnum : kotlin.Enum<MyEnum> {
+    enum entry A
+
+    private constructor MyEnum()
+    public const final val inEnum: kotlin.Int = 17
+    protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: MyEnum): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun name(): kotlin.String
+    public final override /*1*/ /*fake_override*/ fun ordinal(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): MyEnum
+    public final /*synthesized*/ fun values(): kotlin.Array<MyEnum>
+}
+
+public final class Outer {
+    public constructor Outer()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    public final inner class Inner {
+        public constructor Inner()
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+        public object C {
+            private constructor C()
+            public const final val a: kotlin.Int = 18
+            public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+            public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+            public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+        }
+    }
+}

compiler/testData/diagnostics/tests/modifiers/const/constInteraction.kt

@@ -0,0 +1,18 @@
+const val aConst = 1
+const val bConst = aConst + 1
+
+const val boolVal = bConst > 1 || (B.boolVal && A.boolVal)
+const val stringInterpolation = "Result: ${B.boolVal}"
+
+object A {
+    const val boolVal = bConst + 3 == 5
+
+    const val recursive1: Int = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>1 + B.recursive2<!>
+}
+
+class B {
+    companion object {
+        const val boolVal = A.boolVal
+        const val recursive2: Int = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>A.recursive1 + 2<!>
+    }
+}

compiler/testData/diagnostics/tests/modifiers/const/constInteraction.txt

@@ -0,0 +1,31 @@
+package
+
+public const val aConst: kotlin.Int = 1
+public const val bConst: kotlin.Int = 2
+public const val boolVal: kotlin.Boolean = true
+public const val stringInterpolation: kotlin.String = "Result: true"
+
+public object A {
+    private constructor A()
+    public const final val boolVal: kotlin.Boolean = true
+    public const final val recursive1: kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class B {
+    public constructor B()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open 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 const final val boolVal: kotlin.Boolean = true
+        public const final val recursive2: kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}

compiler/testData/diagnostics/tests/modifiers/const/types.kt

@@ -0,0 +1,16 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+const val intConst = 1
+const val longConst: Long = 1
+const val boolConst = true
+const val stringConst = "empty"
+
+enum class MyEnum { A }
+
+<!TYPE_CANT_BE_USED_FOR_CONST_VAL!>const<!> val enumConst: MyEnum = MyEnum.A
+<!TYPE_CANT_BE_USED_FOR_CONST_VAL!>const<!> val arrayConst: Array<String> = arrayOf("1")
+<!TYPE_CANT_BE_USED_FOR_CONST_VAL!>const<!> val intArrayConst: IntArray = intArrayOf()
+
+// ------------------------------------------------
+fun <T> arrayOf(vararg x: T): Array<T> = null!!
+fun intArrayOf(): IntArray = null!!

compiler/testData/diagnostics/tests/modifiers/const/types.txt

@@ -0,0 +1,28 @@
+package
+
+public const val arrayConst: kotlin.Array<kotlin.String>
+public const val boolConst: kotlin.Boolean = true
+public const val enumConst: MyEnum
+public const val intArrayConst: kotlin.IntArray
+public const val intConst: kotlin.Int = 1
+public const val longConst: kotlin.Long = 1.toLong()
+public const val stringConst: kotlin.String = "empty"
+public fun </*0*/ T> arrayOf(/*0*/ vararg x: T /*kotlin.Array<out T>*/): kotlin.Array<T>
+public fun intArrayOf(): kotlin.IntArray
+
+public final enum class MyEnum : kotlin.Enum<MyEnum> {
+    enum entry A
+
+    private constructor MyEnum()
+    protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
+    public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: MyEnum): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final override /*1*/ /*fake_override*/ fun name(): kotlin.String
+    public final override /*1*/ /*fake_override*/ fun ordinal(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final /*synthesized*/ fun valueOf(/*0*/ value: kotlin.String): MyEnum
+    public final /*synthesized*/ fun values(): kotlin.Array<MyEnum>
+}