FIR checker: warn useless elvis

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/deadCodeInBinaryExpressions.fir.kt

@@ -8,7 +8,7 @@ fun testBinary2() {
 }
 
 fun testElvis1() {
-    todo() ?: ""
+    todo() <!USELESS_ELVIS!>?: ""<!>
 }
 
 fun testElvis2(s: String?) {
@@ -36,4 +36,4 @@ fun returnInBinary2(): Boolean {
 }
 
 fun todo(): Nothing = throw Exception()
-fun bar() {}
+fun bar() {}

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/deadCodeInWhileFromBreak.fir.kt

@@ -50,6 +50,6 @@ fun test(arr: Array<Int>) {
     }
 
     while (true) {
-        break ?: null
+        break <!USELESS_ELVIS!>?: null<!>
     }
 }

compiler/testData/diagnostics/tests/controlFlowAnalysis/elvisNotProcessed.fir.kt

@@ -2,20 +2,20 @@
 // See KT-8277
 // NI_EXPECTED_FILE
 
-val v = { true } ?: ( { true } ?:null!! )
+val v = { true } <!USELESS_ELVIS!>?: ( { true } <!USELESS_ELVIS!>?:null!!<!> )<!>
 
 val w = if (true) {
     { true }
 }
 else {
-    { true } ?: null!!
+    { true } <!USELESS_ELVIS!>?: null!!<!>
 }
 
 val ww = if (true) {
-    { true } ?: null!!
+    { true } <!USELESS_ELVIS!>?: null!!<!>
 }
 else if (true) {
-    { true } ?: null!!
+    { true } <!USELESS_ELVIS!>?: null!!<!>
 }
 else {
     null!!
@@ -29,11 +29,11 @@ val b = null ?: ( l() ?: false)
 
 val bb = null ?: ( l() ?: null!!)
 
-val bbb = null ?: ( l() ?: null)
+val bbb = null ?: ( l() <!USELESS_ELVIS_RIGHT_IS_NULL!>?: null<!>)
 
-val bbbb = ( l() ?: null) ?: ( l() ?: null)
+val bbbb = ( l() <!USELESS_ELVIS_RIGHT_IS_NULL!>?: null<!>) ?: ( l() <!USELESS_ELVIS_RIGHT_IS_NULL!>?: null<!>)
 
 fun f(x : Long?): Long {
-    var a = x ?: (fun() {} ?: fun() {})
+    var a = x ?: (fun() {} <!USELESS_ELVIS!>?: fun() {}<!>)
     return <!RETURN_TYPE_MISMATCH!>a<!>
 }

compiler/testData/diagnostics/tests/controlFlowAnalysis/throwInLambda.fir.kt

@@ -7,6 +7,6 @@ fun foo(): String {
 }
 fun bar(): String {
     val x = fn() ?: return ""
-    val y = x<!UNNECESSARY_SAFE_CALL!>?.<!>let { throw Exception() } ?: "unreachable"
+    val y = x<!UNNECESSARY_SAFE_CALL!>?.<!>let { throw Exception() } <!USELESS_ELVIS!>?: "unreachable"<!>
     return y
 }