KT-22274 report warning on labels that can't be referenced

Labels are meaningful only if they can be referenced by 'break',
'continue', or 'return' expressions.

compiler/testData/diagnostics/tests/controlStructures/notAFunctionLabel_after.kt

@@ -51,12 +51,12 @@ fun testLoopLabelInReturn(xs: List<Int>) {
 }
 
 fun testValLabelInReturn() {
-    L@ val fn = { <!NOT_A_FUNCTION_LABEL!>return@L<!> }
+    <!REDUNDANT_LABEL_WARNING!>L@<!> val fn = { <!NOT_A_FUNCTION_LABEL!>return@L<!> }
     fn()
 }
 
 fun testHighOrderFunctionCallLabelInReturn() {
-    L@ run {
+    <!REDUNDANT_LABEL_WARNING!>L@<!> run {
         <!NOT_A_FUNCTION_LABEL!>return@L<!>
     }
 }

compiler/testData/diagnostics/tests/controlStructures/notAFunctionLabel_before.kt

@@ -51,12 +51,12 @@ fun testLoopLabelInReturn(xs: List<Int>) {
 }
 
 fun testValLabelInReturn() {
-    L@ val fn = { <!NOT_A_FUNCTION_LABEL_WARNING!>return@L<!> }
+    <!REDUNDANT_LABEL_WARNING!>L@<!> val fn = { <!NOT_A_FUNCTION_LABEL_WARNING!>return@L<!> }
     fn()
 }
 
 fun testHighOrderFunctionCallLabelInReturn() {
-    L@ run {
+    <!REDUNDANT_LABEL_WARNING!>L@<!> run {
         <!NOT_A_FUNCTION_LABEL_WARNING!>return@L<!>
     }
 }

compiler/testData/diagnostics/tests/controlStructures/redundantLabel.kt

@@ -0,0 +1,39 @@
+@Target(AnnotationTarget.EXPRESSION)
+@Retention(AnnotationRetention.SOURCE)
+annotation class Ann
+
+fun testLambdaLabel() = l@ { 42 }
+
+fun testAnonymousFunctionLabel() = l@ fun() {}
+
+fun testAnnotatedLambdaLabel() = lambda@ @Ann {}
+
+fun testParenthesizedLambdaLabel() = lambda@ ( {} )
+
+fun testLabelBoundToInvokeOperatorExpression() = <!REDUNDANT_LABEL_WARNING!>l@<!> { 42 }()
+
+fun testLabelBoundToLambda() = (l@ { 42 })()
+
+fun testWhileLoopLabel() {
+    L@ while (true) {}
+}
+
+fun testDoWhileLoopLabel() {
+    L@ do {} while (true)
+}
+
+fun testForLoopLabel(xs: List<Any>) {
+    L@ for (x in xs) {}
+}
+
+fun testValLabel() {
+    <!REDUNDANT_LABEL_WARNING!>L@<!> val fn = {}
+    fn()
+}
+
+fun testHighOrderFunctionCallLabel() {
+    <!REDUNDANT_LABEL_WARNING!>L@<!> run {}
+}
+
+fun testAnonymousObjectLabel() =
+    <!REDUNDANT_LABEL_WARNING!>L@<!> object {}

compiler/testData/diagnostics/tests/controlStructures/redundantLabel.txt

@@ -0,0 +1,21 @@
+package
+
+public fun testAnnotatedLambdaLabel(): () -> kotlin.Unit
+public fun testAnonymousFunctionLabel(): () -> kotlin.Unit
+public fun testAnonymousObjectLabel(): kotlin.Any
+public fun testDoWhileLoopLabel(): kotlin.Unit
+public fun testForLoopLabel(/*0*/ xs: kotlin.collections.List<kotlin.Any>): kotlin.Unit
+public fun testHighOrderFunctionCallLabel(): kotlin.Unit
+public fun testLabelBoundToInvokeOperatorExpression(): kotlin.Int
+public fun testLabelBoundToLambda(): kotlin.Int
+public fun testLambdaLabel(): () -> kotlin.Int
+public fun testParenthesizedLambdaLabel(): () -> kotlin.Unit
+public fun testValLabel(): kotlin.Unit
+public fun testWhileLoopLabel(): kotlin.Unit
+
+@kotlin.annotation.Target(allowedTargets = {AnnotationTarget.EXPRESSION}) @kotlin.annotation.Retention(value = AnnotationRetention.SOURCE) public final annotation class Ann : kotlin.Annotation {
+    public constructor Ann()
+    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
+}