[FIR] Fix various corner cases in DFA

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/dfa/FirDataFlowAnalyzer.kt

@@ -184,7 +184,9 @@ abstract class FirDataFlowAnalyzer<FLOW : Flow>(
                         flow.addTypeStatement(operandVariable typeEq any)
                     }
                     if (isNotNullCheck) {
-                        flow.addImplication((expressionVariable eq true) implies (operandVariable typeEq any)) }
+                        flow.addImplication((expressionVariable eq true) implies (operandVariable typeEq any))
+                        flow.addImplication((expressionVariable eq true) implies (operandVariable notEq null))
+                    }
 
                 } else {
                     if (isNotNullCheck) {
@@ -196,14 +198,13 @@ abstract class FirDataFlowAnalyzer<FLOW : Flow>(
             FirOperation.AS -> {
                 if (operandVariable.isReal()) {
                     flow.addTypeStatement(operandVariable typeEq type)
-                } else {
-                    logicSystem.approveStatementsInsideFlow(
-                        flow,
-                        operandVariable notEq null,
-                        shouldRemoveSynthetics = true,
-                        shouldForkFlow = false
-                    )
                 }
+                logicSystem.approveStatementsInsideFlow(
+                    flow,
+                    operandVariable notEq null,
+                    shouldRemoveSynthetics = true,
+                    shouldForkFlow = false
+                )
             }
 
             FirOperation.SAFE_AS -> {
@@ -329,6 +330,12 @@ abstract class FirDataFlowAnalyzer<FLOW : Flow>(
         val argument = checkNotNullCall.argument
         val operandVariable = variableStorage.getOrCreateRealVariable(argument.symbol, argument) ?: return
         node.flow.addTypeStatement(operandVariable typeEq any)
+        logicSystem.approveStatementsInsideFlow(
+            node.flow,
+            operandVariable notEq null,
+            shouldRemoveSynthetics = true,
+            shouldForkFlow = false
+        )
     }
 
     // ----------------------------------- When -----------------------------------
@@ -511,22 +518,19 @@ abstract class FirDataFlowAnalyzer<FLOW : Flow>(
                 ?.withNullability(ConeNullability.NOT_NULL)
                 ?: return@let
 
-            when (val variable = variableStorage.getOrCreateVariable(receiver)) {
-                is RealVariable -> {
-                    if (shouldFork) {
-                        flow = logicSystem.forkFlow(flow)
-                    }
-                    flow.addTypeStatement(variable typeEq type)
-                }
-                is SyntheticVariable -> {
-                    flow = logicSystem.approveStatementsInsideFlow(
-                        flow,
-                        variable notEq null,
-                        shouldFork,
-                        shouldRemoveSynthetics = true
-                    )
+            val variable = variableStorage.getOrCreateVariable(receiver)
+            if (variable is RealVariable) {
+                if (shouldFork) {
+                    flow = logicSystem.forkFlow(flow)
                 }
+                flow.addTypeStatement(variable typeEq type)
             }
+            flow = logicSystem.approveStatementsInsideFlow(
+                flow,
+                variable notEq null,
+                shouldFork,
+                shouldRemoveSynthetics = true
+            )
         }
 
         node.flow = flow
@@ -654,9 +658,8 @@ abstract class FirDataFlowAnalyzer<FLOW : Flow>(
         variableStorage.getOrCreateRealVariable(initializer.symbol, initializer)?.let { initializerVariable ->
             if (initializerVariable.isStable) {
                 variableStorage.attachSymbolToVariable(variable.symbol, initializerVariable)
-            } else {
-                node.flow.addImplication((propertyVariable notEq null) implies (initializerVariable notEq null))
             }
+            node.flow.addImplication((propertyVariable notEq null) implies (initializerVariable notEq null))
         }
 
         if (!isVariableDeclaration) {

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

@@ -52,7 +52,7 @@ fun kt4565_1(a: SomeClass?) {
         a.data.hashCode()
     }
     if (a?.data is String) {
-        a.<!INAPPLICABLE_CANDIDATE!>data<!>.<!UNRESOLVED_REFERENCE!>length<!>
+        a.data.length
         data.length
     }
 }

compiler/testData/ir/irText/expressions/kt30020.fir.txt

@@ -58,7 +58,8 @@ FILE fqName:<root> fileName:/kt30020.kt
         $receiver: CALL 'public final fun CHECK_NOT_NULL <T0> (arg0: T0 of kotlin.internal.ir.CHECK_NOT_NULL?): T0 of kotlin.internal.ir.CHECK_NOT_NULL declared in kotlin.internal.ir' type=kotlin.collections.MutableList<kotlin.Any> origin=EXCLEXCL
           <T0>: kotlin.collections.MutableList<kotlin.Any>
           arg0: CALL 'public abstract fun f (): kotlin.collections.MutableList<kotlin.Any> declared in <root>.X' type=kotlin.collections.MutableList<kotlin.Any>? origin=null
-            $this: GET_VAR 'nx: <root>.X? declared in <root>.test' type=<root>.X? origin=null
+            $this: TYPE_OP type=<root>.X origin=IMPLICIT_CAST typeOperand=<root>.X
+              GET_VAR 'nx: <root>.X? declared in <root>.test' type=<root>.X? origin=null
         element: CONST Int type=kotlin.Int value=6
   FUN name:testExtensionReceiver visibility:public modality:FINAL <> ($receiver:kotlin.collections.MutableList<kotlin.Any>) returnType:kotlin.Unit
     $receiver: VALUE_PARAMETER name:<this> type:kotlin.collections.MutableList<kotlin.Any>