FIR: record and serialize the modifier "fun" for functional interface

compiler/fir/fir-serialization/src/org/jetbrains/kotlin/fir/serialization/FirElementSerializer.kt

@@ -98,7 +98,7 @@ class FirElementSerializer private constructor(
             regularClass?.isExternal == true,
             regularClass?.isExpect == true,
             regularClass?.isInline == true,
-            false // TODO: klass.isFun not supported yet
+            regularClass?.isFun == true
         )
         if (flags != builder.flags) {
             builder.flags = flags

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrClassifierStorage.kt

@@ -183,7 +183,7 @@ class Fir2IrClassifierStorage(
                     isExternal = regularClass.isExternal,
                     isInline = regularClass.isInline,
                     isExpect = regularClass.isExpect,
-                    isFun = false // TODO FirRegularClass.isFun
+                    isFun = regularClass.isFun
                 ).apply {
                     metadata = FirMetadataSource.Class(regularClass, descriptor)
                     descriptor.bind(this)

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/converter/DeclarationsConverter.kt

@@ -382,6 +382,7 @@ class DeclarationsConverter(
                     isCompanion = modifiers.isCompanion() && classKind == ClassKind.OBJECT
                     isData = modifiers.isDataClass()
                     isInline = modifiers.isInlineClass()
+                    isFun = modifiers.isFunctionalInterface()
                 }
 
                 buildRegularClass {

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/fir/modifier/Modifier.kt

@@ -78,6 +78,10 @@ class Modifier(
         return classModifiers.contains(ClassModifier.COMPANION)
     }
 
+    fun isFunctionalInterface(): Boolean {
+        return classModifiers.contains(ClassModifier.FUN)
+    }
+
     fun hasOverride(): Boolean {
         return memberModifiers.contains(MemberModifier.OVERRIDE)
     }

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/fir/modifier/ModifiersEnumSet.kt

@@ -11,7 +11,8 @@ enum class ClassModifier {
     DATA,
     INLINE,
     INNER,
-    COMPANION
+    COMPANION,
+    FUN
 }
 
 enum class MemberModifier {

compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/RawFirBuilder.kt

@@ -670,6 +670,7 @@ class RawFirBuilder(
                     isCompanion = (classOrObject as? KtObjectDeclaration)?.isCompanion() == true
                     isData = classOrObject.hasModifier(DATA_KEYWORD)
                     isInline = classOrObject.hasModifier(INLINE_KEYWORD)
+                    isFun = classOrObject.hasModifier(FUN_KEYWORD)
                 }
                 withCapturedTypeParameters {
                     if (!status.isInner) context.capturedTypeParameters = context.capturedTypeParameters.clear()

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/declarations/FirDeclarationStatus.kt

@@ -39,6 +39,7 @@ interface FirDeclarationStatus : FirElement {
     val isStatic: Boolean
     val isFromSealedClass: Boolean
     val isFromEnumClass: Boolean
+    val isFun: Boolean
 
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R = visitor.visitDeclarationStatus(this, data)
 }

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/declarations/FirResolvedDeclarationStatus.kt

@@ -38,6 +38,7 @@ interface FirResolvedDeclarationStatus : FirDeclarationStatus {
     override val isStatic: Boolean
     override val isFromSealedClass: Boolean
     override val isFromEnumClass: Boolean
+    override val isFun: Boolean
 
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R = visitor.visitResolvedDeclarationStatus(this, data)
 }

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/FirDeclarationUtil.kt

@@ -37,6 +37,7 @@ inline val FirRegularClass.isInner get() = status.isInner
 inline val FirRegularClass.isCompanion get() = status.isCompanion
 inline val FirRegularClass.isData get() = status.isData
 inline val FirRegularClass.isInline get() = status.isInline
+inline val FirRegularClass.isFun get() = status.isFun
 inline val FirMemberDeclaration.modality get() = status.modality
 inline val FirMemberDeclaration.visibility get() = status.visibility
 inline val FirMemberDeclaration.allowsToHaveFakeOverride: Boolean

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/impl/FirDeclarationStatusImpl.kt

@@ -136,6 +136,12 @@ open class FirDeclarationStatusImpl(
             this[FROM_ENUM] = value
         }
 
+    override var isFun: Boolean
+        get() = this[FUN]
+        set(value) {
+            this[FUN] = value
+        }
+
     private enum class Modifier(val mask: Int) {
         EXPECT(0x1),
         ACTUAL(0x2),
@@ -153,7 +159,8 @@ open class FirDeclarationStatusImpl(
         SUSPEND(0x2000),
         STATIC(0x4000),
         FROM_SEALED(0x8000),
-        FROM_ENUM(0x10000)
+        FROM_ENUM(0x10000),
+        FUN(0x20000)
     }
 
     override fun <R, D> acceptChildren(visitor: FirVisitor<R, D>, data: D) {}

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

@@ -323,7 +323,7 @@ object NodeConfigurator : AbstractFieldConfigurator<FirTreeBuilder>(FirTreeBuild
             generateBooleanFields(
                 "expect", "actual", "override", "operator", "infix", "inline", "tailRec",
                 "external", "const", "lateInit", "inner", "companion", "data", "suspend", "static",
-                "fromSealedClass", "fromEnumClass"
+                "fromSealedClass", "fromEnumClass", "fun"
             )
         }