FIR: suppress VARIABLE_EXPECTED for error reference

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

@@ -495,8 +495,8 @@ open class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransform
         // following `!!` is safe since `operatorIsSuccessful = true` implies `operatorCallReference != null`
         val operatorReturnTypeMatches = operatorIsSuccessful && operatorReturnTypeMatches(operatorCallReference!!.candidate)
 
-        val lhsReference = leftArgument.toResolvedCallableReference()
-        val lhsSymbol = lhsReference?.resolvedSymbol as? FirVariableSymbol<*>
+        val lhsReference = leftArgument.toReference()
+        val lhsSymbol = (lhsReference as? FirResolvedNamedReference)?.resolvedSymbol as? FirVariableSymbol<*>
         val lhsVariable = lhsSymbol?.fir
         val lhsIsVar = lhsVariable?.isVar == true
 
@@ -528,7 +528,12 @@ open class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransform
                                     leftArgument.calleeReference.source
                                 else -> leftArgument.source
                             }
-                            diagnostic = if (lhsSymbol == null) ConeVariableExpectedError else ConeValReassignmentError(lhsSymbol)
+                            diagnostic = when {
+                                // Use a stub diagnostic to suppress unresolved error here because it would be reported by other logic
+                                lhsReference is FirErrorNamedReference -> ConeStubDiagnostic(ConeUnresolvedReferenceError())
+                                lhsSymbol == null -> ConeVariableExpectedError
+                                else -> ConeValReassignmentError(lhsSymbol)
+                            }
                         }
                     }
                     (leftArgument as? FirQualifiedAccess)?.let {

compiler/fir/tree/src/org/jetbrains/kotlin/fir/expressions/FirExpressionUtil.kt

@@ -56,8 +56,12 @@ inline val FirCall.argumentMapping: LinkedHashMap<FirExpression, FirValueParamet
     }
 
 fun FirExpression.toResolvedCallableReference(): FirResolvedNamedReference? {
+    return toReference() as? FirResolvedNamedReference
+}
+
+fun FirExpression.toReference(): FirReference? {
     if (this is FirWrappedArgumentExpression) return expression.toResolvedCallableReference()
-    return (this as? FirResolvable)?.calleeReference as? FirResolvedNamedReference
+    return (this as? FirResolvable)?.calleeReference
 }
 
 fun FirExpression.toResolvedCallableSymbol(): FirCallableSymbol<*>? {

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/AssignmentOperation.fir.kt

@@ -7,7 +7,7 @@ fun bar1(x: Number, y: Int) {
 }
 
 fun bar2(x: Number) {
-    <!UNRESOLVED_REFERENCE, VARIABLE_EXPECTED!>y<!> += x as Int
+    <!UNRESOLVED_REFERENCE!>y<!> += x as Int
     checkSubtype<Int>(x)
 }
 

compiler/testData/diagnostics/tests/incompleteCode/incompleteAssignment.fir.kt

@@ -7,7 +7,7 @@ fun sum(a : IntArray) : Int {
     // Write your solution here
     <!UNRESOLVED_REFERENCE!>res<!> = 0
     for (e in a)
-        <!UNRESOLVED_REFERENCE, VARIABLE_EXPECTED!>res<!> +=<!SYNTAX!><!>
+        <!UNRESOLVED_REFERENCE!>res<!> +=<!SYNTAX!><!>
 <!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY{LT}!>}<!>
 fun main() {
     test(0)

compiler/testData/diagnostics/tests/resolve/dslMarker/properties.fir.kt

@@ -35,11 +35,11 @@ fun test() {
 
         bar {
             <!DSL_SCOPE_VIOLATION!>a<!> + 1
-            <!DSL_SCOPE_VIOLATION, VARIABLE_EXPECTED!>a<!> += <!DSL_SCOPE_VIOLATION!>a<!> + 1
+            <!DSL_SCOPE_VIOLATION!>a<!> += <!DSL_SCOPE_VIOLATION!>a<!> + 1
             <!DSL_SCOPE_VIOLATION, DSL_SCOPE_VIOLATION!>a<!>++
 
             <!DSL_SCOPE_VIOLATION!>a1<!> + 1
-            <!DSL_SCOPE_VIOLATION, VARIABLE_EXPECTED!>a1<!> += <!DSL_SCOPE_VIOLATION!>a1<!> + 1
+            <!DSL_SCOPE_VIOLATION!>a1<!> += <!DSL_SCOPE_VIOLATION!>a1<!> + 1
             <!DSL_SCOPE_VIOLATION, DSL_SCOPE_VIOLATION!>a1<!>++
 
             this@foo.a + 1