FIR: Make constraint injector treat stub types as type variables

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

@@ -432,6 +432,12 @@ interface ConeTypeContext : TypeSystemContext, TypeSystemOptimizationContext, Ty
         return this is ConeStubTypeForBuilderInference
     }
 
+    override fun TypeConstructorMarker.unwrapStubTypeVariableConstructor(): TypeConstructorMarker {
+        if (this !is ConeStubTypeConstructor) return this
+        if (this.isTypeVariableInSubtyping) return this
+        return this.variable.typeConstructor
+    }
+
     override fun intersectTypes(types: List<SimpleTypeMarker>): SimpleTypeMarker {
         @Suppress("UNCHECKED_CAST")
         return ConeTypeIntersector.intersectTypes(this as ConeInferenceContext, types as List<ConeKotlinType>) as SimpleTypeMarker

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt

@@ -47,6 +47,8 @@ interface IrTypeSystemContext : TypeSystemContext, TypeSystemCommonSuperTypesCon
 
     override fun SimpleTypeMarker.isStubTypeForBuilderInference() = false
 
+    override fun TypeConstructorMarker.unwrapStubTypeVariableConstructor(): TypeConstructorMarker = this
+
     override fun FlexibleTypeMarker.asDynamicType() = this as? IrDynamicType
 
     override fun FlexibleTypeMarker.asRawType(): RawTypeMarker? = null

compiler/resolution.common/src/org/jetbrains/kotlin/resolve/calls/inference/components/ConstraintInjector.kt

@@ -293,7 +293,7 @@ class ConstraintInjector(
 
         // from AbstractTypeCheckerContextForConstraintSystem
         override fun isMyTypeVariable(type: SimpleTypeMarker): Boolean =
-            c.allTypeVariables.containsKey(type.typeConstructor())
+            c.allTypeVariables.containsKey(type.typeConstructor().unwrapStubTypeVariableConstructor())
 
         override fun addUpperConstraint(typeVariable: TypeConstructorMarker, superType: KotlinTypeMarker) =
             addConstraint(typeVariable, superType, UPPER)
@@ -326,7 +326,7 @@ class ConstraintInjector(
             kind: ConstraintKind,
             isFromNullabilityConstraint: Boolean = false
         ) {
-            val typeVariable = c.allTypeVariables[typeVariableConstructor]
+            val typeVariable = c.allTypeVariables[typeVariableConstructor.unwrapStubTypeVariableConstructor()]
                 ?: error("Should by type variableConstructor: $typeVariableConstructor. ${c.allTypeVariables.values}")
 
             addNewIncorporatedConstraint(

core/compiler.common/src/org/jetbrains/kotlin/types/model/TypeSystemContext.kt

@@ -358,6 +358,7 @@ interface TypeSystemContext : TypeSystemOptimizationContext {
     fun SimpleTypeMarker.isStubType(): Boolean
     fun SimpleTypeMarker.isStubTypeForVariableInSubtyping(): Boolean
     fun SimpleTypeMarker.isStubTypeForBuilderInference(): Boolean
+    fun TypeConstructorMarker.unwrapStubTypeVariableConstructor(): TypeConstructorMarker
 
     fun KotlinTypeMarker.asTypeArgument(): TypeArgumentMarker
 

core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt

@@ -100,6 +100,10 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         return this is StubTypeForBuilderInference || isDefNotNullStubType<StubTypeForBuilderInference>()
     }
 
+    override fun TypeConstructorMarker.unwrapStubTypeVariableConstructor(): TypeConstructorMarker {
+        return this
+    }
+
     override fun StubTypeMarker.getOriginalTypeVariable(): TypeVariableTypeConstructorMarker {
         require(this is AbstractStubType, this::errorMessage)
         return this.originalTypeVariable as TypeVariableTypeConstructorMarker