[FIR] Fix taking symbol of expression with smartcast inside DFA

compiler/fir/analysis-tests/legacy-fir-tests/tests-gen/org/jetbrains/kotlin/fir/LazyBodyIsNotTouchedTilContractsPhaseTestGenerated.java

@@ -2944,6 +2944,11 @@ public class LazyBodyIsNotTouchedTilContractsPhaseTestGenerated extends Abstract
             public void testFunctionCallBound() throws Exception {
                 runTest("compiler/fir/analysis-tests/testData/resolve/smartcasts/boundSmartcasts/functionCallBound.kt");
             }
+
+            @TestMetadata("thisAssignment.kt")
+            public void testThisAssignment() throws Exception {
+                runTest("compiler/fir/analysis-tests/testData/resolve/smartcasts/boundSmartcasts/thisAssignment.kt");
+            }
         }
 
         @TestMetadata("compiler/fir/analysis-tests/testData/resolve/smartcasts/controlStructures")

compiler/fir/analysis-tests/testData/resolve/smartcasts/boundSmartcasts/thisAssignment.fir.txt

@@ -0,0 +1,14 @@
+FILE: thisAssignment.kt
+    public abstract interface A : R|kotlin/Any| {
+        public abstract fun foo(): R|kotlin/Unit|
+
+    }
+    public final fun R|kotlin/Any|.test(): R|kotlin/Unit| {
+        when () {
+            (this@R|/test| is R|A|) ->  {
+                lval a: R|kotlin/Any| = this@R|/test|
+                R|<local>/a|.R|/A.foo|()
+            }
+        }
+
+    }

compiler/fir/analysis-tests/testData/resolve/smartcasts/boundSmartcasts/thisAssignment.kt

@@ -0,0 +1,12 @@
+interface A {
+    fun foo()
+}
+
+fun Any.test() {
+    if (this is A) {
+        val a = this
+        a.foo()
+    }
+}
+
+

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

@@ -3323,6 +3323,12 @@ public class FirDiagnosticTestGenerated extends AbstractFirDiagnosticTest {
                 public void testFunctionCallBound() throws Exception {
                     runTest("compiler/fir/analysis-tests/testData/resolve/smartcasts/boundSmartcasts/functionCallBound.kt");
                 }
+
+                @Test
+                @TestMetadata("thisAssignment.kt")
+                public void testThisAssignment() throws Exception {
+                    runTest("compiler/fir/analysis-tests/testData/resolve/smartcasts/boundSmartcasts/thisAssignment.kt");
+                }
             }
 
             @Nested

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

@@ -3362,6 +3362,12 @@ public class FirDiagnosticsWithLightTreeTestGenerated extends AbstractFirDiagnos
                 public void testFunctionCallBound() throws Exception {
                     runTest("compiler/fir/analysis-tests/testData/resolve/smartcasts/boundSmartcasts/functionCallBound.kt");
                 }
+
+                @Test
+                @TestMetadata("thisAssignment.kt")
+                public void testThisAssignment() throws Exception {
+                    runTest("compiler/fir/analysis-tests/testData/resolve/smartcasts/boundSmartcasts/thisAssignment.kt");
+                }
             }
 
             @Nested

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

@@ -99,7 +99,7 @@ internal val FirElement.symbol: AbstractFirBasedSymbol<*>?
         is FirWhenSubjectExpression -> whenRef.value.subject?.symbol
         is FirSafeCallExpression -> regularQualifiedAccess.symbol
         else -> null
-    }?.takeIf { this is FirThisReceiverExpression || (it !is FirFunctionSymbol<*> && it !is FirAccessorSymbol) }
+    }?.takeIf { this.unwrapSmartcastExpression() is FirThisReceiverExpression || (it !is FirFunctionSymbol<*> && it !is FirAccessorSymbol) }
 
 @DfaInternals
 internal val FirResolvable.symbol: AbstractFirBasedSymbol<*>?
@@ -109,3 +109,5 @@ internal val FirResolvable.symbol: AbstractFirBasedSymbol<*>?
         is FirNamedReferenceWithCandidate -> reference.candidateSymbol
         else -> null
     }
+
+private fun FirElement.unwrapSmartcastExpression(): FirElement = if (this is FirExpressionWithSmartcast) originalExpression else this