[FIR] Assume SafeCallsAreAlwaysNullable is always on

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

@@ -8,7 +8,6 @@ package org.jetbrains.kotlin.fir.resolve
 import org.jetbrains.kotlin.KtFakeSourceElementKind
 import org.jetbrains.kotlin.KtSourceElement
 import org.jetbrains.kotlin.builtins.functions.FunctionTypeKind
-import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.fakeElement
@@ -493,25 +492,15 @@ fun FirCheckedSafeCallSubject.propagateTypeFromOriginalReceiver(
 }
 
 fun FirSafeCallExpression.propagateTypeFromQualifiedAccessAfterNullCheck(
-    nullableReceiverExpression: FirExpression,
     session: FirSession,
     file: FirFile,
 ) {
-    val receiverType = nullableReceiverExpression.typeRef.coneTypeSafe<ConeKotlinType>()
     val selector = selector
 
     val resultingType = when {
         selector is FirExpression && !selector.isCallToStatementLikeFunction -> {
             val type = selector.typeRef.coneTypeSafe<ConeKotlinType>() ?: return
-
-            val isReceiverActuallyNullable = session.languageVersionSettings.supportsFeature(LanguageFeature.SafeCallsAreAlwaysNullable)
-                    || receiverType != null && session.typeContext.run { receiverType.isNullableType() }
-
-            if (isReceiverActuallyNullable) {
-                type.withNullability(ConeNullability.NULLABLE, session.typeContext)
-            } else {
-                type
-            }
+            type.withNullability(ConeNullability.NULLABLE, session.typeContext)
         }
         // Branch for things that shouldn't be used as expressions.
         // They are forced to return not-null `Unit`, regardless of the receiver.

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirCallCompletionResultsWriterTransformer.kt

@@ -343,7 +343,7 @@ class FirCallCompletionResultsWriterTransformer(
             )?.toExpectedType()
         )
 
-        safeCallExpression.propagateTypeFromQualifiedAccessAfterNullCheck(safeCallExpression.receiver, session, context.file)
+        safeCallExpression.propagateTypeFromQualifiedAccessAfterNullCheck(session, context.file)
 
         return safeCallExpression
     }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt

@@ -357,7 +357,7 @@ open class FirExpressionsResolveTransformer(transformer: FirAbstractBodyResolveT
                 safeCallExpression.apply {
                     checkedSubjectRef.value.propagateTypeFromOriginalReceiver(receiver, components.session, components.file)
                     transformSelector(this@FirExpressionsResolveTransformer, data)
-                    propagateTypeFromQualifiedAccessAfterNullCheck(receiver, session, context.file)
+                    propagateTypeFromQualifiedAccessAfterNullCheck(session, context.file)
                 }
 
                 dataFlowAnalyzer.exitSafeCall(safeCallExpression)

compiler/testData/codegen/bytecodeText/nullCheckOptimization/redundantSafeCall_1_4.kt

@@ -1,4 +1,7 @@
 // !LANGUAGE: -SafeCallsAreAlwaysNullable
+// IGNORE_BACKEND_K2: JVM_IR
+// Status: Feature is always on in K2
+
 fun test(s: String) = s?.length
 
 // 0 IFNULL

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

@@ -0,0 +1,7 @@
+// !LANGUAGE: -SafeCallsAreAlwaysNullable
+// http://youtrack.jetbrains.net/issue/KT-418
+
+fun ff() {
+    val i: Int = 1
+    val a: Int = <!INITIALIZER_TYPE_MISMATCH!>i<!SAFE_CALL_WILL_CHANGE_NULLABILITY!><!UNNECESSARY_SAFE_CALL!>?.<!>plus(2)<!><!>
+}

compiler/testData/diagnostics/tests/SafeCallNonNullReceiver.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // !LANGUAGE: -SafeCallsAreAlwaysNullable
 // http://youtrack.jetbrains.net/issue/KT-418
 

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

@@ -8,6 +8,6 @@ fun foo(): String {
 }
 fun bar(): String {
     val x = fn() ?: return ""
-    val y = x<!SAFE_CALL_WILL_CHANGE_NULLABILITY!><!UNNECESSARY_SAFE_CALL!>?.<!>let { throw Exception() }<!> <!USELESS_ELVIS!>?: "unreachable"<!>
+    val y = x<!SAFE_CALL_WILL_CHANGE_NULLABILITY!><!UNNECESSARY_SAFE_CALL!>?.<!>let { throw Exception() }<!> ?: "unreachable"
     return y
 }

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

@@ -0,0 +1,34 @@
+// LANGUAGE: -SafeCallsAreAlwaysNullable
+// DIAGNOSTICS: -UNNECESSARY_SAFE_CALL
+// ISSUE: KT-46860
+
+interface A {
+    fun id(): A
+
+    fun foo(): String
+}
+
+fun test_1(a: A) {
+    val s = a.id().id().id().id().id().id().id().id()<!SAFE_CALL_WILL_CHANGE_NULLABILITY!>?.foo()<!><!UNSAFE_CALL!>.<!>length
+}
+
+fun test_2(a: A) {
+    val s = a.id()
+        .id()
+        .id()
+        .id()
+        <!SAFE_CALL_WILL_CHANGE_NULLABILITY!>?.id()<!>
+        <!UNSAFE_CALL!>.<!>id()
+        .id()
+        .id()
+        <!SAFE_CALL_WILL_CHANGE_NULLABILITY!>?.foo()<!>
+        ?.length
+}
+
+fun test_3(a: A) {
+    val s = a.id()<!SAFE_CALL_WILL_CHANGE_NULLABILITY!>?.
+        id()<!><!UNSAFE_CALL!>.<!>
+        id()<!SAFE_CALL_WILL_CHANGE_NULLABILITY!>?.
+        foo()<!><!UNSAFE_CALL!>.<!>
+        length
+}

compiler/testData/diagnostics/tests/nullableTypes/safeCallOnNotNullableType.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 // LANGUAGE: -SafeCallsAreAlwaysNullable
 // DIAGNOSTICS: -UNNECESSARY_SAFE_CALL
 // ISSUE: KT-46860