FIR checkers: report VAL_REASSIGNMENT for assignment operators

Currently VAL_REASSIGNMENT are only reported on direct assignments.
Reassignments in the form of, for example, `+=` are reported as
`VARIABLE_EXPECTED`, which differs from FE1.0.

compiler/fir/analysis-tests/testData/resolve/arguments/fieldPlusAssign.fir.txt

@@ -6,6 +6,6 @@ FILE: fieldPlusAssign.kt
         }
     public final val y: R|kotlin/Int| = Int(1)
         public get(): R|kotlin/Int| {
-            <Variable expected># = F|/y|.R|kotlin/Int.plus|(Int(1))
+            <Re-assigning a val variable># = F|/y|.R|kotlin/Int.plus|(Int(1))
             ^ Int(1)
         }

compiler/fir/analysis-tests/testData/resolve/arguments/fieldPlusAssign.kt

@@ -5,6 +5,6 @@ var x: Int = 1
 
 val y: Int = 1
     get() {
-        <!VARIABLE_EXPECTED!>field<!> += 1
+        <!VAL_REASSIGNMENT_VIA_BACKING_FIELD_ERROR!>field<!> += 1
         return 1
     }

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt

@@ -23,6 +23,7 @@ import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassLikeSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirVariableSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
 import org.jetbrains.kotlin.name.Name
@@ -483,13 +484,13 @@ object DIAGNOSTICS_LIST : DiagnosticList() {
             parameter<FirPropertySymbol>("variable")
         }
         val VAL_REASSIGNMENT by error<FirSourceElement, KtExpression> {
-            parameter<FirPropertySymbol>("variable")
+            parameter<FirVariableSymbol<*>>("variable")
         }
         val VAL_REASSIGNMENT_VIA_BACKING_FIELD by warning<FirSourceElement, KtExpression> {
-            parameter<FirPropertySymbol>("variable")
+            parameter<FirPropertySymbol>("property")
         }
         val VAL_REASSIGNMENT_VIA_BACKING_FIELD_ERROR by error<FirSourceElement, KtExpression> {
-            parameter<FirPropertySymbol>("variable")
+            parameter<FirPropertySymbol>("property")
         }
         val WRONG_INVOCATION_KIND by warning<FirSourceElement, PsiElement> {
             parameter<AbstractFirBasedSymbol<*>>("declaration")

compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt

@@ -23,6 +23,7 @@ import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassLikeSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirVariableSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
 import org.jetbrains.kotlin.name.Name
@@ -296,7 +297,7 @@ object FirErrors {
 
     // Control flow diagnostics
     val UNINITIALIZED_VARIABLE by error1<FirSourceElement, KtSimpleNameExpression, FirPropertySymbol>()
-    val VAL_REASSIGNMENT by error1<FirSourceElement, KtExpression, FirPropertySymbol>()
+    val VAL_REASSIGNMENT by error1<FirSourceElement, KtExpression, FirVariableSymbol<*>>()
     val VAL_REASSIGNMENT_VIA_BACKING_FIELD by warning1<FirSourceElement, KtExpression, FirPropertySymbol>()
     val VAL_REASSIGNMENT_VIA_BACKING_FIELD_ERROR by error1<FirSourceElement, KtExpression, FirPropertySymbol>()
     val WRONG_INVOCATION_KIND by warning3<FirSourceElement, PsiElement, AbstractFirBasedSymbol<*>, EventOccurrencesRange, EventOccurrencesRange>()

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt

@@ -14,12 +14,12 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.FIR
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.FQ_NAMES_IN_TYPES
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.NAME
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.NULLABLE_STRING
-import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.PROPERTY_NAME
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.RENDER_CLASS_OR_OBJECT
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.RENDER_TYPE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.SYMBOL
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.SYMBOLS
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.TO_STRING
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.VARIABLE_NAME
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.VISIBILITY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirDiagnosticRenderers.WHEN_MISSING_CASES
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.ABSENCE_OF_PRIMARY_CONSTRUCTOR_FOR_INLINE_CLASS
@@ -646,10 +646,10 @@ class FirDefaultErrorMessages : DefaultErrorMessages.Extension {
             )
 
             // Control flow diagnostics
-            map.put(UNINITIALIZED_VARIABLE, "{0} must be initialized before access", PROPERTY_NAME)
+            map.put(UNINITIALIZED_VARIABLE, "{0} must be initialized before access", VARIABLE_NAME)
-            map.put(VAL_REASSIGNMENT, "Val cannot be reassigned", PROPERTY_NAME)
+            map.put(VAL_REASSIGNMENT, "Val cannot be reassigned", VARIABLE_NAME)
-            map.put(VAL_REASSIGNMENT_VIA_BACKING_FIELD, "Reassignment of read-only property via backing field is deprecated", PROPERTY_NAME)
+            map.put(VAL_REASSIGNMENT_VIA_BACKING_FIELD, "Reassignment of read-only property via backing field is deprecated", VARIABLE_NAME)
-            map.put(VAL_REASSIGNMENT_VIA_BACKING_FIELD_ERROR, "Reassignment of read-only property via backing field", PROPERTY_NAME)
+            map.put(VAL_REASSIGNMENT_VIA_BACKING_FIELD_ERROR, "Reassignment of read-only property via backing field", VARIABLE_NAME)
             map.put(
                 WRONG_INVOCATION_KIND,
                 "{2} wrong invocation kind: given {3} case, but {4} case is possible",

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDiagnosticRenderers.kt

@@ -14,10 +14,7 @@ import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.render
 import org.jetbrains.kotlin.fir.renderWithType
 import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
-import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.*
-import org.jetbrains.kotlin.fir.symbols.impl.FirClassLikeSymbol
-import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
-import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.fir.types.render
 
@@ -43,7 +40,7 @@ object FirDiagnosticRenderers {
         element.toString()
     }
 
-    val PROPERTY_NAME = Renderer { symbol: FirPropertySymbol ->
+    val VARIABLE_NAME = Renderer { symbol: FirVariableSymbol<*> ->
         symbol.fir.name.asString()
     }
 

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/coneDiagnosticToFirDiagnostic.kt

@@ -18,6 +18,7 @@ import org.jetbrains.kotlin.fir.resolve.calls.NamedArgumentNotAllowed
 import org.jetbrains.kotlin.fir.resolve.calls.ResolutionDiagnostic
 import org.jetbrains.kotlin.fir.resolve.calls.VarargArgumentOutsideParentheses
 import org.jetbrains.kotlin.fir.resolve.diagnostics.*
+import org.jetbrains.kotlin.fir.symbols.impl.FirBackingFieldSymbol
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.resolve.calls.tower.isSuccess
@@ -39,6 +40,10 @@ private fun ConeDiagnostic.toFirDiagnostic(
     }
     is ConeOperatorAmbiguityError -> FirErrors.ASSIGN_OPERATOR_AMBIGUITY.on(source, this.candidates)
     is ConeVariableExpectedError -> FirErrors.VARIABLE_EXPECTED.on(source)
+    is ConeValReassignmentError -> when (val symbol = this.variable) {
+        is FirBackingFieldSymbol -> FirErrors.VAL_REASSIGNMENT_VIA_BACKING_FIELD_ERROR.on(source, symbol.fir.symbol)
+        else -> FirErrors.VAL_REASSIGNMENT.on(source, symbol)
+    }
     is ConeTypeMismatchError -> FirErrors.TYPE_MISMATCH.on(qualifiedAccessSource ?: source, this.expectedType, this.actualType)
     is ConeUnexpectedTypeArgumentsError -> FirErrors.TYPE_ARGUMENTS_NOT_ALLOWED.on(this.source.safeAs() ?: source)
     is ConeIllegalAnnotationError -> FirErrors.NOT_AN_ANNOTATION_CLASS.on(source, this.name.asString())

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/diagnostics/FirDiagnostics.kt

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassLikeSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirVariableSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.Name
@@ -59,6 +60,10 @@ class ConeVariableExpectedError : ConeDiagnostic() {
     override val reason: String get() = "Variable expected"
 }
 
+class ConeValReassignmentError(val variable: FirVariableSymbol<*>) : ConeDiagnostic() {
+    override val reason: String get() = "Re-assigning a val variable"
+}
+
 class ConeTypeMismatchError(val expectedType: ConeKotlinType, val actualType: ConeKotlinType) : ConeDiagnostic() {
     override val reason: String
         get() = "Type mismatch. Expected: $expectedType, Actual: $actualType"

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

@@ -385,7 +385,8 @@ open class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransform
         val operatorIsError = operatorCallReference?.isError ?: true
 
         val lhsReference = leftArgument.toResolvedCallableReference()
-        val lhsVariable = (lhsReference?.resolvedSymbol as? FirVariableSymbol<*>)?.fir
+        val lhsSymbol = lhsReference?.resolvedSymbol as? FirVariableSymbol<*>
+        val lhsVariable = lhsSymbol?.fir
         val lhsIsVar = lhsVariable?.isVar == true
         return when {
             operatorIsError || (!lhsIsVar && !assignIsError) -> {
@@ -409,7 +410,7 @@ open class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransform
                                         leftArgument.calleeReference.source
                                     else -> leftArgument.source
                                 }
-                                diagnostic = ConeVariableExpectedError()
+                                diagnostic = if (lhsSymbol == null) ConeVariableExpectedError() else ConeValReassignmentError(lhsSymbol)
                             }
                         }
                         (leftArgument as? FirQualifiedAccess)?.let {

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

@@ -103,7 +103,7 @@ class Test() {
         a += 34
         (l@ a) += 34
 
-        <!VARIABLE_EXPECTED!>b<!> += 34
+        <!VAL_REASSIGNMENT!>b<!> += 34
 
         a++
         (l@ a)++
@@ -113,9 +113,9 @@ class Test() {
     fun testVariables1() {
         val b: Int = 34
 
-        (l@ <!VARIABLE_EXPECTED!>b<!>) += 34
+        (l@ <!VAL_REASSIGNMENT!>b<!>) += 34
         //repeat for b
-        (<!VARIABLE_EXPECTED!>b<!>) += 3
+        (<!VAL_REASSIGNMENT!>b<!>) += 3
     }
 
     fun testArrays(a: Array<Int>, ab: Ab) {

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

@@ -89,18 +89,18 @@ fun t3() {
 
 fun t4() {
     val x = 1
-    <!VARIABLE_EXPECTED!>x<!> += 2
+    <!VAL_REASSIGNMENT!>x<!> += 2
     val y = 3
-    <!VARIABLE_EXPECTED!>y<!> *= 4
+    <!VAL_REASSIGNMENT!>y<!> *= 4
     var z = 5
     z -= y
 }
 
 fun t5() {
     for (i in 0..2) {
-        <!VARIABLE_EXPECTED!>i<!> += 1
+        <!VAL_REASSIGNMENT!>i<!> += 1
         fun t5() {
-            <!VARIABLE_EXPECTED!>i<!> += 3
+            <!VAL_REASSIGNMENT!>i<!> += 3
         }
     }
 }
@@ -213,7 +213,7 @@ class LocalValsVsProperties(val a: Int, w: Int) : Open(a, w) {
     var xx = w
     var yy : Int
     init {
-        <!VARIABLE_EXPECTED!>w<!> += 1
+        <!VAL_REASSIGNMENT!>w<!> += 1
         yy = w
     }
 }

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

@@ -68,16 +68,16 @@ class Test1 {
 
     init {
         inlineMe {
-            <!VARIABLE_EXPECTED!>a<!> += "allowed"
+            <!VAL_REASSIGNMENT!>a<!> += "allowed"
         }
         crossinlineMe {
-            <!VARIABLE_EXPECTED!>b<!> += "not allowed"
+            <!VAL_REASSIGNMENT!>b<!> += "not allowed"
         }
         noinlineMe {
-            <!VARIABLE_EXPECTED!>c<!> += "not allowed"
+            <!VAL_REASSIGNMENT!>c<!> += "not allowed"
         }
         notinline {
-            <!VARIABLE_EXPECTED!>d<!> += "not allowed"
+            <!VAL_REASSIGNMENT!>d<!> += "not allowed"
         }
     }
 }

compiler/testData/diagnostics/tests/controlFlowAnalysis/kt1571.fir.kt

@@ -31,7 +31,7 @@ fun box() : String {
     if (c1 != 1) {
         return "2"
     }
-    <!VARIABLE_EXPECTED!>a<!> *= 3 // a = a * 3, shouldn't be able to do this on val
+    <!VAL_REASSIGNMENT!>a<!> *= 3 // a = a * 3, shouldn't be able to do this on val
     if (c0 != 2) {
         return "3"
     }

idea/idea-frontend-fir/idea-frontend-fir-generator/src/org/jetbrains/kotlin/idea/frontend/api/fir/generator/HLDiagnosticConverter.kt

@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.fir.symbols.AbstractFirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassLikeSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirVariableSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.fir.types.FirTypeRef
 import org.jetbrains.kotlin.idea.frontend.api.symbols.*
@@ -174,6 +175,11 @@ private object FirToKtConversionCreator {
             KtVariableSymbol::class.createType(),
             importsToAdd = listOf("org.jetbrains.kotlin.fir.declarations.FirProperty")
         ),
+        FirVariableSymbol::class to HLFunctionCallConversion(
+            "firSymbolBuilder.variableLikeBuilder.buildVariableLikeSymbol({0}.fir)",
+            KtVariableLikeSymbol::class.createType(),
+            importsToAdd = listOf("org.jetbrains.kotlin.fir.declarations.FirVariable")
+        ),
     )
 
     private val allowedTypesWithoutTypeParams = setOf(

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDataClassConverters.kt

@@ -14,6 +14,7 @@ import org.jetbrains.kotlin.fir.declarations.FirClass
 import org.jetbrains.kotlin.fir.declarations.FirDeclaration
 import org.jetbrains.kotlin.fir.declarations.FirProperty
 import org.jetbrains.kotlin.fir.declarations.FirTypeParameter
+import org.jetbrains.kotlin.fir.declarations.FirVariable
 import org.jetbrains.kotlin.fir.psi
 import org.jetbrains.kotlin.psi.KtArrayAccessExpression
 import org.jetbrains.kotlin.psi.KtClassOrObject
@@ -1346,7 +1347,7 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
     }
     add(FirErrors.VAL_REASSIGNMENT) { firDiagnostic ->
         ValReassignmentImpl(
-            firSymbolBuilder.variableLikeBuilder.buildVariableSymbol(firDiagnostic.a.fir as FirProperty),
+            firSymbolBuilder.variableLikeBuilder.buildVariableLikeSymbol(firDiagnostic.a.fir),
             firDiagnostic as FirPsiDiagnostic<*>,
             token,
         )

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -17,6 +17,7 @@ import org.jetbrains.kotlin.idea.frontend.api.symbols.KtCallableSymbol
 import org.jetbrains.kotlin.idea.frontend.api.symbols.KtClassLikeSymbol
 import org.jetbrains.kotlin.idea.frontend.api.symbols.KtSymbol
 import org.jetbrains.kotlin.idea.frontend.api.symbols.KtTypeParameterSymbol
+import org.jetbrains.kotlin.idea.frontend.api.symbols.KtVariableLikeSymbol
 import org.jetbrains.kotlin.idea.frontend.api.symbols.KtVariableSymbol
 import org.jetbrains.kotlin.idea.frontend.api.types.KtType
 import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
@@ -951,17 +952,17 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
 
     abstract class ValReassignment : KtFirDiagnostic<KtExpression>() {
         override val diagnosticClass get() = ValReassignment::class
-        abstract val variable: KtVariableSymbol
+        abstract val variable: KtVariableLikeSymbol
     }
 
     abstract class ValReassignmentViaBackingField : KtFirDiagnostic<KtExpression>() {
         override val diagnosticClass get() = ValReassignmentViaBackingField::class
-        abstract val variable: KtVariableSymbol
+        abstract val property: KtVariableSymbol
     }
 
     abstract class ValReassignmentViaBackingFieldError : KtFirDiagnostic<KtExpression>() {
         override val diagnosticClass get() = ValReassignmentViaBackingFieldError::class
-        abstract val variable: KtVariableSymbol
+        abstract val property: KtVariableSymbol
     }
 
     abstract class WrongInvocationKind : KtFirDiagnostic<PsiElement>() {

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -18,6 +18,7 @@ import org.jetbrains.kotlin.idea.frontend.api.symbols.KtCallableSymbol
 import org.jetbrains.kotlin.idea.frontend.api.symbols.KtClassLikeSymbol
 import org.jetbrains.kotlin.idea.frontend.api.symbols.KtSymbol
 import org.jetbrains.kotlin.idea.frontend.api.symbols.KtTypeParameterSymbol
+import org.jetbrains.kotlin.idea.frontend.api.symbols.KtVariableLikeSymbol
 import org.jetbrains.kotlin.idea.frontend.api.symbols.KtVariableSymbol
 import org.jetbrains.kotlin.idea.frontend.api.tokens.ValidityToken
 import org.jetbrains.kotlin.idea.frontend.api.types.KtType
@@ -1536,7 +1537,7 @@ internal class UninitializedVariableImpl(
 }
 
 internal class ValReassignmentImpl(
-    override val variable: KtVariableSymbol,
+    override val variable: KtVariableLikeSymbol,
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,
 ) : KtFirDiagnostic.ValReassignment(), KtAbstractFirDiagnostic<KtExpression> {
@@ -1544,7 +1545,7 @@ internal class ValReassignmentImpl(
 }
 
 internal class ValReassignmentViaBackingFieldImpl(
-    override val variable: KtVariableSymbol,
+    override val property: KtVariableSymbol,
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,
 ) : KtFirDiagnostic.ValReassignmentViaBackingField(), KtAbstractFirDiagnostic<KtExpression> {
@@ -1552,7 +1553,7 @@ internal class ValReassignmentViaBackingFieldImpl(
 }
 
 internal class ValReassignmentViaBackingFieldErrorImpl(
-    override val variable: KtVariableSymbol,
+    override val property: KtVariableSymbol,
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,
 ) : KtFirDiagnostic.ValReassignmentViaBackingFieldError(), KtAbstractFirDiagnostic<KtExpression> {