[FE 1.0] Make type of safe call always nullable

^KT-46860 In Progress

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsTestGenerated.java

@@ -27416,6 +27416,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                     runTest("compiler/testData/diagnostics/tests/smartCasts/safecalls/safeAccessReceiverNotNull.kt");
                 }
 
+                @Test
+                @TestMetadata("safeCallIsAlwaysNullable.kt")
+                public void testSafeCallIsAlwaysNullable() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/smartCasts/safecalls/safeCallIsAlwaysNullable.kt");
+                }
+
                 @Test
                 @TestMetadata("simple.kt")
                 public void testSimple() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirOldFrontendDiagnosticsWithLightTreeTestGenerated.java

@@ -27416,6 +27416,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                     runTest("compiler/testData/diagnostics/tests/smartCasts/safecalls/safeAccessReceiverNotNull.kt");
                 }
 
+                @Test
+                @TestMetadata("safeCallIsAlwaysNullable.kt")
+                public void testSafeCallIsAlwaysNullable() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/smartCasts/safecalls/safeCallIsAlwaysNullable.kt");
+                }
+
                 @Test
                 @TestMetadata("simple.kt")
                 public void testSimple() throws Exception {

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/CallExpressionResolver.kt

@@ -359,8 +359,10 @@ class CallExpressionResolver(
             KotlinTypeInfo {
         var initialDataFlowInfoForArguments = context.dataFlowInfo
         val receiverDataFlowValue = (receiver as? ReceiverValue)?.let { dataFlowValueFactory.createDataFlowValue(it, context) }
-        val receiverCanBeNull = receiverDataFlowValue != null &&
+
-                initialDataFlowInfoForArguments.getStableNullability(receiverDataFlowValue).canBeNull()
+        val receiverCanBeNull = receiverDataFlowValue != null && initialDataFlowInfoForArguments.getStableNullability(receiverDataFlowValue).canBeNull()
+        val shouldNullifySafeCallType =
+            receiverCanBeNull || context.languageVersionSettings.supportsFeature(LanguageFeature.SafeCallsAreAlwaysNullable)
 
         val callOperationNode = AstLoadingFilter.forceAllowTreeLoading(element.qualified.containingFile, ThrowableComputable {
             element.node
@@ -368,11 +370,12 @@ class CallExpressionResolver(
 
         if (receiverDataFlowValue != null && element.safe) {
             // Additional "receiver != null" information should be applied if we consider a safe call
-            if (receiverCanBeNull) {
+            if (shouldNullifySafeCallType) {
                 initialDataFlowInfoForArguments = initialDataFlowInfoForArguments.disequate(
                     receiverDataFlowValue, DataFlowValue.nullValue(builtIns), languageVersionSettings
                 )
-            } else {
+            }
+            if (!receiverCanBeNull) {
                 reportUnnecessarySafeCall(context.trace, receiver.type, callOperationNode, receiver)
             }
         }
@@ -393,7 +396,7 @@ class CallExpressionResolver(
 
         val selectorType = selectorTypeInfo.type
         if (selectorType != null) {
-            if (element.safe && receiverCanBeNull) {
+            if (element.safe && shouldNullifySafeCallType) {
                 selectorTypeInfo = selectorTypeInfo.replaceType(TypeUtils.makeNullable(selectorType))
             }
             // TODO : this is suspicious: remove this code?

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

@@ -5,4 +5,4 @@ fun test(s: String) = s?.length
 // 0 IFNULL
 // 0 IFNONNULL
 // 0 intValue
-// 0 valueOf
+// 1 valueOf

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

@@ -0,0 +1,20 @@
+// LANGUAGE: +SafeCallsAreAlwaysNullable
+// ISSUE: KT-46860
+
+interface A {
+    fun foo(): Int
+}
+
+fun takeInt(x: Int) {}
+
+fun test_1(a: A) {
+    val x = <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Int")!>a<!UNNECESSARY_SAFE_CALL!>?.<!>foo()<!>
+    takeInt(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()<!>
+        takeInt(x) // should be an error
+    }
+}

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

@@ -0,0 +1,20 @@
+// LANGUAGE: +SafeCallsAreAlwaysNullable
+// ISSUE: KT-46860
+
+interface A {
+    fun foo(): Int
+}
+
+fun takeInt(x: Int) {}
+
+fun test_1(a: A) {
+    val x = <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.Int?")!>a<!UNNECESSARY_SAFE_CALL!>?.<!>foo()<!>
+    takeInt(<!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()<!>
+        takeInt(<!TYPE_MISMATCH!>x<!>) // should be an error
+    }
+}

compiler/testData/diagnostics/tests/smartCasts/safecalls/safeCallIsAlwaysNullable.txt

@@ -0,0 +1,12 @@
+package
+
+public fun takeInt(/*0*/ x: kotlin.Int): kotlin.Unit
+public fun test_1(/*0*/ a: A): kotlin.Unit
+public fun test_2(/*0*/ a: A?): kotlin.Unit
+
+public interface A {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -27506,6 +27506,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                     runTest("compiler/testData/diagnostics/tests/smartCasts/safecalls/safeAccessReceiverNotNull.kt");
                 }
 
+                @Test
+                @TestMetadata("safeCallIsAlwaysNullable.kt")
+                public void testSafeCallIsAlwaysNullable() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/smartCasts/safecalls/safeCallIsAlwaysNullable.kt");
+                }
+
                 @Test
                 @TestMetadata("simple.kt")
                 public void testSimple() throws Exception {

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

@@ -211,6 +211,7 @@ enum class LanguageFeature(
     UnrestrictedBuilderInference(KOTLIN_1_6),
     ProperTypeInferenceConstraintsProcessing(KOTLIN_1_6, kind = BUG_FIX),
     ClassTypeParameterAnnotations(KOTLIN_1_6),
+    SafeCallsAreAlwaysNullable(KOTLIN_1_6),
 
     // Temporarily disabled, see KT-27084/KT-22379
     SoundSmartcastFromLoopConditionForLoopAssignedVariables(sinceVersion = null, kind = BUG_FIX),

idea/idea-frontend-fir/idea-fir-low-level-api/tests/org/jetbrains/kotlin/idea/fir/low/level/api/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java

@@ -27416,6 +27416,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                     runTest("compiler/testData/diagnostics/tests/smartCasts/safecalls/safeAccessReceiverNotNull.kt");
                 }
 
+                @Test
+                @TestMetadata("safeCallIsAlwaysNullable.kt")
+                public void testSafeCallIsAlwaysNullable() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/smartCasts/safecalls/safeCallIsAlwaysNullable.kt");
+                }
+
                 @Test
                 @TestMetadata("simple.kt")
                 public void testSimple() throws Exception {