[FIR IDE] Add KtImportOptimizer mixin and FIR implementation

Does nothing for now

idea/idea-frontend-api/src/org/jetbrains/kotlin/idea/frontend/api/KtAnalysisSession.kt

@@ -48,6 +48,7 @@ public abstract class KtAnalysisSession(final override val token: ValidityToken)
     KtSymbolsMixIn,
     KtReferenceResolveMixIn,
     KtReferenceShortenerMixIn,
+    KtImportOptimizerMixIn,
     KtSymbolDeclarationRendererMixIn,
     KtVisibilityCheckerMixIn,
     KtMemberSymbolProviderMixin,
@@ -88,6 +89,9 @@ public abstract class KtAnalysisSession(final override val token: ValidityToken)
     internal val referenceShortener: KtReferenceShortener get() = referenceShortenerImpl
     protected abstract val referenceShortenerImpl: KtReferenceShortener
 
+    internal val importOptimizer: KtImportOptimizer get() = importOptimizerImpl
+    protected abstract val importOptimizerImpl: KtImportOptimizer
+
     internal val symbolDeclarationRendererProvider: KtSymbolDeclarationRendererProvider get() = symbolDeclarationRendererProviderImpl
     protected abstract val symbolDeclarationRendererProviderImpl: KtSymbolDeclarationRendererProvider
 

idea/idea-frontend-api/src/org/jetbrains/kotlin/idea/frontend/api/components/KtImportOptimizer.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010-2021 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.frontend.api.components
+
+import org.jetbrains.kotlin.psi.KtFile
+import org.jetbrains.kotlin.psi.KtImportDirective
+
+public abstract class KtImportOptimizer {
+    public abstract fun analyseImports(file: KtFile): KtImportOptimizerResult
+}
+
+public interface KtImportOptimizerMixIn : KtAnalysisSessionMixIn {
+    public fun analyseImports(file: KtFile): KtImportOptimizerResult {
+        return analysisSession.importOptimizer.analyseImports(file)
+    }
+}
+
+public class KtImportOptimizerResult(
+    public val unusedImports: Set<KtImportDirective>,
+)

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/KtFirAnalysisSession.kt

@@ -64,6 +64,8 @@ private constructor(
 
     override val referenceShortenerImpl = KtFirReferenceShortener(this, token, firResolveState)
 
+    override val importOptimizerImpl: KtImportOptimizer = KtFirImportOptimizer()
+
     override val symbolDeclarationRendererProviderImpl: KtSymbolDeclarationRendererProvider =
         KtFirSymbolDeclarationRendererProvider(this, token)
 

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/components/KtFirImportOptimizer.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2010-2021 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.frontend.api.fir.components
+
+import org.jetbrains.kotlin.idea.frontend.api.components.KtImportOptimizer
+import org.jetbrains.kotlin.idea.frontend.api.components.KtImportOptimizerResult
+import org.jetbrains.kotlin.psi.KtFile
+
+internal class KtFirImportOptimizer : KtImportOptimizer() {
+    override fun analyseImports(file: KtFile): KtImportOptimizerResult {
+        return KtImportOptimizerResult(emptySet())
+    }
+}