New default checks for mixed hierarchies

Old and new schemes

idea/idea-analysis/src/org/jetbrains/kotlin/idea/compiler/IdeLanguageVersionSettingsProvider.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2010-2020 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.idea.compiler
+
+import org.jetbrains.kotlin.analyzer.moduleInfo
+import org.jetbrains.kotlin.config.LanguageVersionSettings
+import org.jetbrains.kotlin.descriptors.ModuleDescriptor
+import org.jetbrains.kotlin.idea.caches.project.ModuleSourceInfo
+import org.jetbrains.kotlin.idea.project.languageVersionSettings
+import org.jetbrains.kotlin.resolve.LanguageVersionSettingsProvider
+
+class IdeLanguageVersionSettingsProvider : LanguageVersionSettingsProvider {
+    override fun getModuleLanguageVersionSettings(module: ModuleDescriptor): LanguageVersionSettings? {
+        // downcast to module source info, as we're not interested in non-source classes
+        val moduleInfo = module.moduleInfo as? ModuleSourceInfo ?: return null
+        return moduleInfo.module.languageVersionSettings
+    }
+}

idea/resources/META-INF/plugin-common.xml

@@ -196,6 +196,9 @@
     <projectService serviceInterface="org.jetbrains.kotlin.resolve.ModuleAnnotationsResolver"
                     serviceImplementation="org.jetbrains.kotlin.idea.compiler.IdeModuleAnnotationsResolver"/>
 
+    <projectService serviceInterface="org.jetbrains.kotlin.resolve.LanguageVersionSettingsProvider"
+                    serviceImplementation="org.jetbrains.kotlin.idea.compiler.IdeLanguageVersionSettingsProvider"/>
+
     <projectService serviceInterface="org.jetbrains.kotlin.asJava.LightClassGenerationSupport"
                     serviceImplementation="org.jetbrains.kotlin.idea.caches.resolve.IDELightClassGenerationSupport"/>