FIR: implement resolve of unqualified enum references in when

See KT-16768

compiler/fir/providers/src/org/jetbrains/kotlin/fir/scopes/impl/FirExplicitStarImportingScope.kt

@@ -10,7 +10,7 @@ import org.jetbrains.kotlin.fir.declarations.FirImport
 import org.jetbrains.kotlin.fir.declarations.FirResolvedImport
 import org.jetbrains.kotlin.fir.resolve.ScopeSession
 
-class FirExplicitStarImportingScope(
+open class FirExplicitStarImportingScope(
     imports: List<FirImport>,
     session: FirSession,
     scopeSession: ScopeSession,

compiler/fir/providers/src/org/jetbrains/kotlin/fir/scopes/impl/FirWhenSubjectImportingScope.kt

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.scopes.impl
+
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.declarations.builder.buildImport
+import org.jetbrains.kotlin.fir.declarations.builder.buildResolvedImport
+import org.jetbrains.kotlin.fir.resolve.ScopeSession
+import org.jetbrains.kotlin.fir.resolve.substitution.ConeSubstitutor
+import org.jetbrains.kotlin.fir.symbols.impl.FirClassifierSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirEnumEntrySymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirVariableSymbol
+import org.jetbrains.kotlin.name.ClassId
+import org.jetbrains.kotlin.name.Name
+
+// Note: at this moment we create this scope for enum classes only,
+// and only enum entry symbols are allowed to be processed
+class FirWhenSubjectImportingScope(
+    classId: ClassId, session: FirSession, scopeSession: ScopeSession
+) : FirExplicitStarImportingScope(
+    listOf(buildResolvedImportByClassId(classId)),
+    session, scopeSession, FirImportingScopeFilter.ALL
+) {
+    override fun processPropertiesByName(name: Name, processor: (FirVariableSymbol<*>) -> Unit) {
+        super.processPropertiesByName(name) {
+            if (it is FirEnumEntrySymbol) {
+                processor(it)
+            }
+        }
+    }
+
+    override fun processFunctionsByName(name: Name, processor: (FirNamedFunctionSymbol) -> Unit) {
+    }
+
+    override fun processClassifiersByNameWithSubstitution(name: Name, processor: (FirClassifierSymbol<*>, ConeSubstitutor) -> Unit) {
+    }
+
+    companion object {
+        private fun buildResolvedImportByClassId(classId: ClassId) = buildResolvedImport {
+            delegate = buildImport {
+                importedFqName = classId.asSingleFqName()
+                isAllUnder = true
+            }
+            packageFqName = classId.packageFqName
+            relativeParentClassName = classId.relativeClassName
+        }
+    }
+}