FIR DFA: align return-implies checker closer to smartcasts

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/cfa/FirReturnsImpliesAnalyzer.kt

@@ -195,8 +195,10 @@ object FirReturnsImpliesAnalyzer : FirControlFlowChecker() {
     }
 
     private fun RealVariable.nullabilityStatement(builtinTypes: BuiltinTypes, isNull: Boolean) =
-        // TODO: opposite for builtinTypes.nullableNothingType.type
-        if (isNull) this typeNotEq builtinTypes.anyType.type else this typeEq builtinTypes.anyType.type
+        if (isNull)
+            this typeEq builtinTypes.nullableNothingType.type andTypeNotEq builtinTypes.anyType.type
+        else
+            this typeEq builtinTypes.anyType.type andTypeNotEq builtinTypes.nullableNothingType.type
 
     private fun TypeStatement.singleton(): TypeStatements =
         mapOf(variable to this)

compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/nullabilitySmartcastWhenNullability.fir.kt

@@ -31,9 +31,9 @@ fun testNullWhenNull(x: Int?) {
 
 // NB. it is the same function as `nullWhenNull`, but annotations specifies other facet of the function behaviour
 fun notNullWhenNotNull (x: Int?): Int? {
-    contract {
+    <!WRONG_IMPLIES_CONDITION!>contract {
         returns(null) implies (x == null)
-    }
+    }<!>
     return x?.inc()
 }
 

compiler/tests-spec/testData/diagnostics/notLinked/contracts/analysis/common/neg/1.fir.kt

@@ -20,7 +20,7 @@ inline fun case_1(value_1: Int?, block: () -> Unit): Boolean {
 
 // TESTCASE NUMBER: 2
 inline fun <T> T?.case_2(value_1: Int?, value_2: Any?, block: () -> Unit): Boolean? {
-    <!WRONG_IMPLIES_CONDITION!>contract {
+    <!WRONG_IMPLIES_CONDITION, WRONG_IMPLIES_CONDITION!>contract {
         callsInPlace(block, InvocationKind.AT_MOST_ONCE)
         returns(true) implies (value_1 == null && this@case_2 == null && value_2 !is Boolean?)
         returns(false) implies (value_2 is Boolean?)

compiler/tests-spec/testData/diagnostics/notLinked/contracts/analysis/smartcasts/neg/8.fir.kt

@@ -8,7 +8,7 @@ import kotlin.contracts.*
 
 // TESTCASE NUMBER: 3
 fun <T> T?.case_3(value_1: Int?, value_2: Boolean): Boolean {
-    <!WRONG_IMPLIES_CONDITION!>contract {
+    <!WRONG_IMPLIES_CONDITION, WRONG_IMPLIES_CONDITION!>contract {
         returns(true) implies (value_1 != null)
         returns(false) implies (value_1 == null && !value_2)
         returns(null) implies (value_1 == null && value_2)
@@ -30,7 +30,7 @@ fun case_4(value_1: Number, block: (() -> Unit)?): Boolean? {
 
 // TESTCASE NUMBER: 5
 fun String?.case_5(value_1: Number?): Boolean? {
-    <!WRONG_IMPLIES_CONDITION!>contract {
+    <!WRONG_IMPLIES_CONDITION, WRONG_IMPLIES_CONDITION!>contract {
         returns(true) implies (value_1 == null)
         returns(false) implies (this@case_5 == null)
         returnsNotNull() implies (value_1 is Int)
@@ -41,7 +41,7 @@ fun String?.case_5(value_1: Number?): Boolean? {
 
 // TESTCASE NUMBER: 6
 fun <T> T?.case_6(value_1: Number, value_2: String?): Boolean? {
-    <!WRONG_IMPLIES_CONDITION!>contract {
+    <!WRONG_IMPLIES_CONDITION, WRONG_IMPLIES_CONDITION, WRONG_IMPLIES_CONDITION!>contract {
         returns(true) implies (this@case_6 == null)
         returns(false) implies (value_1 is Int)
         returns(null) implies (this@case_6 is String)

compiler/tests-spec/testData/diagnostics/notLinked/contracts/analysis/smartcasts/pos/8.fir.kt

@@ -19,11 +19,11 @@ fun <T> T?.case_3(value_1: Int?, value_2: Boolean): Boolean {
 
 // TESTCASE NUMBER: 4
 fun case_4(value_1: Number, block: (() -> Unit)?): Boolean? {
-    contract {
+    <!WRONG_IMPLIES_CONDITION!>contract {
         returns(true) implies (value_1 is Int)
         returns(false) implies (block == null)
         returns(null) implies (block != null)
-    }
+    }<!>
 
     return <!SENSELESS_COMPARISON!>value_1 == null<!>
 }