[FIR] Make type of safe call always nullable

^KT-46860 In Progress

compiler/fir/analysis-tests/testData/resolve/extendedCheckers/RedundantCallOfConversionMethod/safeString.kt

@@ -3,4 +3,4 @@
 fun test() {
     val foo: String? = null
     foo?.<!REDUNDANT_CALL_OF_CONVERSION_METHOD!>toString()<!>
-}
+}

compiler/fir/analysis-tests/testData/resolve/extendedCheckers/UselessCallOnNotNullChecker/NullOrEmptySafe.kt

@@ -1,4 +1,4 @@
 // WITH_RUNTIME
 
 val s: String? = ""
-val empty = s?.<!USELESS_CALL_ON_NOT_NULL!>isNullOrEmpty()<!>
+val empty = s?.<!USELESS_CALL_ON_NOT_NULL!>isNullOrEmpty()<!>

compiler/fir/analysis-tests/testData/resolve/extendedCheckers/UselessCallOnNotNullChecker/SafeCall.kt

@@ -1,4 +1,4 @@
 // WITH_RUNTIME
 
 val list1: List<Int>? = listOf(1)
-val list = list1?.<!USELESS_CALL_ON_NOT_NULL!>orEmpty()<!>
+val list = list1?.<!USELESS_CALL_ON_NOT_NULL!>orEmpty()<!>

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/ResolveUtils.kt

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.fir.resolve
 
 import org.jetbrains.kotlin.builtins.StandardNames
 import org.jetbrains.kotlin.builtins.functions.FunctionClassKind
+import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.fir.*
 import org.jetbrains.kotlin.fir.declarations.*
@@ -343,8 +344,11 @@ fun FirSafeCallExpression.propagateTypeFromQualifiedAccessAfterNullCheck(
 ) {
     val receiverType = nullableReceiverExpression.typeRef.coneTypeSafe<ConeKotlinType>()
     val typeAfterNullCheck = regularQualifiedAccess.expressionTypeOrUnitForAssignment() ?: return
-    val isReceiverActuallyNullable = receiverType != null && session.typeContext.run { receiverType.isNullableType() }
+    val isReceiverActuallyNullable = if (session.languageVersionSettings.supportsFeature(LanguageFeature.SafeCallsAreAlwaysNullable)) {
-
+        true
+    } else {
+        receiverType != null && session.typeContext.run { receiverType.isNullableType() }
+    }
     val resultingType =
         if (isReceiverActuallyNullable)
             typeAfterNullCheck.withNullability(ConeNullability.NULLABLE, session.typeContext)

compiler/testData/diagnostics/tests/SafeCallNonNullReceiverReturnNull.fir.kt

@@ -2,5 +2,5 @@ fun Int.gg() = null
 
 fun ff() {
     val a: Int = 1
-    val b: Int = <!INITIALIZER_TYPE_MISMATCH!>a<!UNNECESSARY_SAFE_CALL!>?.<!><!TYPE_MISMATCH!>gg()<!><!>
+    val b: Int = <!INITIALIZER_TYPE_MISMATCH, TYPE_MISMATCH!>a<!UNNECESSARY_SAFE_CALL!>?.<!>gg()<!>
 }

compiler/testData/diagnostics/tests/j+k/sam/enhancedSamConstructor.fir.kt

@@ -18,10 +18,10 @@ fun main() {
     J <!ARGUMENT_TYPE_MISMATCH!>{ s: String -> s}<!> // should be prohibited, because SAM value parameter has nullable type
     J { "" + it<!UNSAFE_CALL!>.<!>length }
     J { <!NULL_FOR_NONNULL_TYPE!>null<!> }
-    J { it?.length?.<!ARGUMENT_TYPE_MISMATCH!>toString()<!> }
+    J { <!ARGUMENT_TYPE_MISMATCH!>it?.length?.toString()<!> }
 
     J2 <!ARGUMENT_TYPE_MISMATCH!>{ s: String -> s}<!>
     J2 { "" + it<!UNSAFE_CALL!>.<!>length }
     J2 { <!NULL_FOR_NONNULL_TYPE!>null<!> }
-    J2 { it?.length?.<!ARGUMENT_TYPE_MISMATCH!>toString()<!> }
+    J2 { <!ARGUMENT_TYPE_MISMATCH!>it?.length?.toString()<!> }
 }

compiler/testData/diagnostics/tests/nullableTypes/safeCallWithInvoke.fir.kt

@@ -8,5 +8,5 @@ fun foo(i: Int) = i
 
 fun test(a: A?) {
     a?.b(1) //should be no warning
-    foo(a?.<!ARGUMENT_TYPE_MISMATCH!>b(1)<!>) //no warning, only error
+    foo(<!ARGUMENT_TYPE_MISMATCH!>a?.b(1)<!>) //no warning, only error
 }

compiler/testData/diagnostics/tests/resolve/nestedCalls/kt5971NestedSafeCall.fir.kt

@@ -6,5 +6,5 @@
 fun foo(i: Int) {}
 
 fun test(s: String?) {
-    foo(<!ARGUMENT_TYPE_MISMATCH{PSI}!>s?.<!ARGUMENT_TYPE_MISMATCH{LT}!>length<!><!>)
+    foo(<!ARGUMENT_TYPE_MISMATCH!>s?.length<!>)
 }

compiler/testData/diagnostics/tests/smartCasts/safecalls/safeCallIsAlwaysNullable.fir.kt

@@ -8,13 +8,13 @@ interface A {
 fun takeInt(x: Int) {}
 
 fun test_1(a: A) {
-    val x = <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Int")!>a<!UNNECESSARY_SAFE_CALL!>?.<!>foo()<!>
+    val x = <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Int?")!>a<!UNNECESSARY_SAFE_CALL!>?.<!>foo()<!>
-    takeInt(x) // should be an error
+    takeInt(<!ARGUMENT_TYPE_MISMATCH!>x<!>) // should be an error
 }
 
 fun test_2(a: A?) {
     if (a != null) {
-        val x = <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Int")!>a<!UNNECESSARY_SAFE_CALL!>?.<!>foo()<!>
+        val x = <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Int?")!>a<!UNNECESSARY_SAFE_CALL!>?.<!>foo()<!>
-        takeInt(x) // should be an error
+        takeInt(<!ARGUMENT_TYPE_MISMATCH!>x<!>) // should be an error
     }
 }