[FIR] Fix false positive USELESS_CAST on stub types, ^KT-50293 Fixed

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirUselessTypeOperationCallChecker.kt

@@ -38,7 +38,11 @@ object FirUselessTypeOperationCallChecker : FirTypeOperatorCallChecker() {
             when (expression.operation) {
                 FirOperation.IS -> reporter.reportOn(expression.source, FirErrors.USELESS_IS_CHECK, true, context)
                 FirOperation.NOT_IS -> reporter.reportOn(expression.source, FirErrors.USELESS_IS_CHECK, false, context)
-                FirOperation.AS, FirOperation.SAFE_AS -> reporter.reportOn(expression.source, FirErrors.USELESS_CAST, context)
+                FirOperation.AS, FirOperation.SAFE_AS -> {
+                    if ((arg.typeRef as? FirResolvedTypeRef)?.isFromStubType != true) {
+                        reporter.reportOn(expression.source, FirErrors.USELESS_CAST, context)
+                    }
+                }
                 else -> throw AssertionError("Should not be here: ${expression.operation}")
             }
         }

compiler/fir/providers/src/org/jetbrains/kotlin/fir/types/TypeUtils.kt

@@ -322,6 +322,7 @@ fun FirTypeRef.withReplacedConeType(
             type = newType
             annotations += this@withReplacedConeType.annotations
             delegatedTypeRef = this@withReplacedConeType.delegatedTypeRef
+            isFromStubType = this@withReplacedConeType.type is ConeStubType
         }
     }
 }

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/declarations/impl/FirErrorFunctionImpl.kt

@@ -52,7 +52,7 @@ internal class FirErrorFunctionImpl(
     override val symbol: FirErrorFunctionSymbol,
 ) : FirErrorFunction() {
     override var status: FirDeclarationStatus = FirResolvedDeclarationStatusImpl.DEFAULT_STATUS_FOR_STATUSLESS_DECLARATIONS
-    override var returnTypeRef: FirTypeRef = FirErrorTypeRefImpl(null, null, diagnostic)
+    override var returnTypeRef: FirTypeRef = FirErrorTypeRefImpl(null, null, diagnostic, false)
     override val receiverTypeRef: FirTypeRef? get() = null
     override var controlFlowGraphReference: FirControlFlowGraphReference? = null
     override val body: FirBlock? get() = null

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/declarations/impl/FirErrorPropertyImpl.kt

@@ -55,7 +55,7 @@ internal class FirErrorPropertyImpl(
 ) : FirErrorProperty() {
     override val typeParameters: List<FirTypeParameterRef> get() = emptyList()
     override var status: FirDeclarationStatus = FirResolvedDeclarationStatusImpl.DEFAULT_STATUS_FOR_STATUSLESS_DECLARATIONS
-    override var returnTypeRef: FirTypeRef = FirErrorTypeRefImpl(null, null, diagnostic)
+    override var returnTypeRef: FirTypeRef = FirErrorTypeRefImpl(null, null, diagnostic, false)
     override val receiverTypeRef: FirTypeRef? get() = null
     override val initializer: FirExpression? get() = null
     override val delegate: FirExpression? get() = null

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/expressions/impl/FirErrorExpressionImpl.kt

@@ -28,7 +28,7 @@ internal class FirErrorExpressionImpl(
     override val diagnostic: ConeDiagnostic,
     override var expression: FirExpression?,
 ) : FirErrorExpression() {
-    override var typeRef: FirTypeRef = FirErrorTypeRefImpl(source, null, ConeStubDiagnostic(diagnostic))
+    override var typeRef: FirTypeRef = FirErrorTypeRefImpl(source, null, ConeStubDiagnostic(diagnostic), false)
 
     override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {
         typeRef.accept(visitor, data)

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/FirErrorTypeRef.kt

@@ -22,6 +22,7 @@ abstract class FirErrorTypeRef : FirResolvedTypeRef(), FirDiagnosticHolder {
     abstract override val annotations: List<FirAnnotation>
     abstract override val type: ConeKotlinType
     abstract override val delegatedTypeRef: FirTypeRef?
+    abstract override val isFromStubType: Boolean
     abstract override val diagnostic: ConeDiagnostic
 
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R = visitor.visitErrorTypeRef(this, data)

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/FirResolvedTypeRef.kt

@@ -20,6 +20,7 @@ abstract class FirResolvedTypeRef : FirTypeRef() {
     abstract override val annotations: List<FirAnnotation>
     abstract val type: ConeKotlinType
     abstract val delegatedTypeRef: FirTypeRef?
+    abstract val isFromStubType: Boolean
 
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R = visitor.visitResolvedTypeRef(this, data)
 

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/builder/FirResolvedTypeRefBuilder.kt

@@ -30,6 +30,7 @@ class FirResolvedTypeRefBuilder : FirAnnotationContainerBuilder {
     override val annotations: MutableList<FirAnnotation> = mutableListOf()
     lateinit var type: ConeKotlinType
     var delegatedTypeRef: FirTypeRef? = null
+    var isFromStubType: Boolean = false
 
     @OptIn(FirImplementationDetail::class)
     override fun build(): FirResolvedTypeRef {
@@ -38,6 +39,7 @@ class FirResolvedTypeRefBuilder : FirAnnotationContainerBuilder {
             annotations,
             type,
             delegatedTypeRef,
+            isFromStubType,
         )
     }
 
@@ -61,5 +63,6 @@ inline fun buildResolvedTypeRefCopy(original: FirResolvedTypeRef, init: FirResol
     copyBuilder.annotations.addAll(original.annotations)
     copyBuilder.type = original.type
     copyBuilder.delegatedTypeRef = original.delegatedTypeRef
+    copyBuilder.isFromStubType = original.isFromStubType
     return copyBuilder.apply(init).build()
 }

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/impl/FirResolvedTypeRefImpl.kt

@@ -25,6 +25,7 @@ class FirResolvedTypeRefImpl @FirImplementationDetail constructor(
     override val annotations: MutableList<FirAnnotation>,
     override val type: ConeKotlinType,
     override var delegatedTypeRef: FirTypeRef?,
+    override val isFromStubType: Boolean,
 ) : FirResolvedTypeRef() {
     override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {
         annotations.forEach { it.accept(visitor, data) }

compiler/fir/tree/src/org/jetbrains/kotlin/fir/types/builder/FirErrorTypeRefBuilder.kt

@@ -37,7 +37,7 @@ class FirErrorTypeRefBuilder : FirAnnotationContainerBuilder {
                 source,
                 type,
                 delegatedTypeRef,
-                diagnostic,
+                diagnostic
             )
         } else {
             FirErrorTypeRefImpl(

compiler/fir/tree/src/org/jetbrains/kotlin/fir/types/impl/FirErrorTypeRefImpl.kt

@@ -19,11 +19,16 @@ internal class FirErrorTypeRefImpl(
     override val type: ConeKotlinType,
     override var delegatedTypeRef: FirTypeRef?,
     override val diagnostic: ConeDiagnostic,
+    override val isFromStubType: Boolean = false
 ) : FirErrorTypeRef() {
-    constructor(source: KtSourceElement?, delegatedTypeRef: FirTypeRef?, diagnostic: ConeDiagnostic) : this(
+    constructor(source: KtSourceElement?, delegatedTypeRef: FirTypeRef?, diagnostic: ConeDiagnostic,
+        isFromStubType: Boolean = false
+    ) : this(
         source,
         ConeErrorType(diagnostic),
-        delegatedTypeRef, diagnostic
+        delegatedTypeRef,
+        diagnostic,
+        isFromStubType
     )
 
     override val annotations: MutableList<FirAnnotation> = mutableListOf()

compiler/fir/tree/src/org/jetbrains/kotlin/fir/types/impl/FirImplicitBuiltinTypeRef.kt

@@ -34,6 +34,9 @@ sealed class FirImplicitBuiltinTypeRef(
     override val delegatedTypeRef: FirTypeRef?
         get() = null
 
+    override val isFromStubType: Boolean
+        get() = false
+
     override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {}
 
     override fun <D> transformChildren(transformer: FirTransformer<D>, data: D): FirElement {

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/BuilderConfigurator.kt

@@ -265,6 +265,7 @@ object BuilderConfigurator : AbstractBuilderConfigurator<FirTreeBuilder>(FirTree
 
         builder(resolvedTypeRef) {
             defaultNull("delegatedTypeRef")
+            default("isFromStubType", "false")
             withCopy()
         }
 

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt

@@ -224,7 +224,7 @@ object ImplementationConfigurator : AbstractFirTreeImplementationConfigurator()
                 "getter", "setter",
                 withGetter = true
             )
-            default("returnTypeRef", "FirErrorTypeRefImpl(null, null, diagnostic)")
+            default("returnTypeRef", "FirErrorTypeRefImpl(null, null, diagnostic, false)")
             useTypes(errorTypeRefImplType)
         }
 
@@ -421,13 +421,13 @@ object ImplementationConfigurator : AbstractFirTreeImplementationConfigurator()
         }
 
         impl(errorExpression) {
-            default("typeRef", "FirErrorTypeRefImpl(source, null, ConeStubDiagnostic(diagnostic))")
+            default("typeRef", "FirErrorTypeRefImpl(source, null, ConeStubDiagnostic(diagnostic), false)")
             useTypes(errorTypeRefImplType, coneStubDiagnosticType)
         }
 
         impl(errorFunction) {
             defaultNull("receiverTypeRef", "body", withGetter = true)
-            default("returnTypeRef", "FirErrorTypeRefImpl(null, null, diagnostic)")
+            default("returnTypeRef", "FirErrorTypeRefImpl(null, null, diagnostic, false)")
             useTypes(errorTypeRefImplType)
         }
 

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/NodeConfigurator.kt

@@ -637,6 +637,7 @@ object NodeConfigurator : AbstractFieldConfigurator<FirTreeBuilder>(FirTreeBuild
         resolvedTypeRef.configure {
             +field("type", coneKotlinTypeType)
             +field("delegatedTypeRef", typeRef, nullable = true)
+            +booleanField("isFromStubType")
         }
 
         typeRefWithNullability.configure {

compiler/testData/diagnostics/tests/inference/builderInference/kt49829.fir.kt

@@ -1,12 +0,0 @@
-// WITH_STDLIB
-// For FIR: see KT-50293
-
-fun main() {
-    val list = buildList {
-        add("one")
-        add("two")
-
-        val secondParameter = get(1)
-        println(secondParameter <!USELESS_CAST!>as String<!>) // WARNING: [CAST_NEVER_SUCCEEDS] This cast can never succeed
-    }
-}

compiler/testData/diagnostics/tests/inference/builderInference/kt49829.kt

@@ -1,5 +1,6 @@
+// FIR_IDENTICAL
 // WITH_STDLIB
-// For FIR: see KT-50293
+// ISSUE: KT-50293
 
 fun main() {
     val list = buildList {
@@ -7,6 +8,6 @@ fun main() {
         add("two")
 
         val secondParameter = get(1)
-        println(secondParameter as String) // WARNING: [CAST_NEVER_SUCCEEDS] This cast can never succeed
+        println(secondParameter as String)
     }
 }