Move resolve during import optimizing to background thread (KT-27106, KT-30018)

#KT-27106 Fixed

idea/src/org/jetbrains/kotlin/idea/imports/KotlinImportOptimizer.kt

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.idea.imports
 
 import com.intellij.lang.ImportOptimizer
+import com.intellij.openapi.application.ApplicationManager
 import com.intellij.openapi.progress.ProgressIndicatorProvider
 import com.intellij.psi.PsiElement
 import com.intellij.psi.PsiFile
@@ -31,7 +32,6 @@ import org.jetbrains.kotlin.idea.references.KtInvokeFunctionReference
 import org.jetbrains.kotlin.idea.references.KtReference
 import org.jetbrains.kotlin.idea.references.canBeResolvedViaImport
 import org.jetbrains.kotlin.idea.references.mainReference
-import org.jetbrains.kotlin.idea.util.application.runWriteAction
 import org.jetbrains.kotlin.idea.util.getResolutionScope
 import org.jetbrains.kotlin.incremental.components.NoLookupLocation
 import org.jetbrains.kotlin.name.FqName
@@ -47,26 +47,29 @@ import java.util.*
 class KotlinImportOptimizer : ImportOptimizer {
     override fun supports(file: PsiFile?) = file is KtFile
 
-    override fun processFile(file: PsiFile?) = Runnable {
-        OptimizeProcess(file as KtFile).execute()
+    override fun processFile(file: PsiFile?): Runnable {
+        val ktFile = (file as? KtFile) ?: return Runnable { /* empty runnable */ }
+        val preparedImports = prepareImports(ktFile) ?: return Runnable { /* empty runnable */ }
+
+        return Runnable {
+            replaceImports(ktFile, preparedImports)
+        }
     }
 
-    private class OptimizeProcess(private val file: KtFile) {
-        fun execute() {
-            val moduleInfo = file.getNullableModuleInfo()
-            if (moduleInfo !is ModuleSourceInfo && moduleInfo !is ScriptModuleInfo) return
+    private fun prepareImports(file: KtFile): List<ImportPath>? {
+        ApplicationManager.getApplication().assertReadAccessAllowed()
 
-            val oldImports = file.importDirectives
-            if (oldImports.isEmpty()) return
+        val moduleInfo = file.getNullableModuleInfo()
+        if (moduleInfo !is ModuleSourceInfo && moduleInfo !is ScriptModuleInfo) return null
 
-            //TODO: keep existing imports? at least aliases (comments)
+        val oldImports = file.importDirectives
+        if (oldImports.isEmpty()) return null
 
-            val descriptorsToImport = collectDescriptorsToImport(file)
+        //TODO: keep existing imports? at least aliases (comments)
 
-            val imports = prepareOptimizedImports(file, descriptorsToImport) ?: return
+        val descriptorsToImport = collectDescriptorsToImport(file)
 
-            runWriteAction { replaceImports(file, imports) }
-        }
+        return prepareOptimizedImports(file, descriptorsToImport)
     }
 
     private class CollectUsedDescriptorsVisitor(file: KtFile) : KtVisitorVoid() {

idea/tests/org/jetbrains/kotlin/idea/folding/FoldingAfterOptimizeImportsTest.kt

@@ -6,16 +6,14 @@
 package org.jetbrains.kotlin.idea.folding
 
 import com.intellij.codeInsight.folding.CodeFoldingManager
-import com.intellij.openapi.command.CommandProcessor
-import com.intellij.openapi.command.UndoConfirmationPolicy
 import com.intellij.openapi.editor.FoldRegion
-import org.jetbrains.kotlin.idea.test.PluginTestCaseBase
-import java.io.File
 import com.intellij.testFramework.fixtures.JavaCodeInsightTestFixture
-import org.jetbrains.kotlin.test.InTextDirectivesUtils
-import com.intellij.openapi.editor.Editor
 import org.jetbrains.kotlin.idea.folding.AbstractKotlinFoldingTest.doTestWithSettings
 import org.jetbrains.kotlin.idea.imports.KotlinImportOptimizer
+import org.jetbrains.kotlin.idea.test.PluginTestCaseBase
+import org.jetbrains.kotlin.idea.util.application.executeWriteCommand
+import org.jetbrains.kotlin.test.InTextDirectivesUtils
+import java.io.File
 
 class FoldingAfterOptimizeImportsTest : AbstractKotlinFoldingTest() {
     private val fixture: JavaCodeInsightTestFixture
@@ -41,11 +39,12 @@ class FoldingAfterOptimizeImportsTest : AbstractKotlinFoldingTest() {
             CodeFoldingManager.getInstance(fixture.project)!!.buildInitialFoldings(editor)
             getFoldingRegion(0).checkRegion(false, findStringWithPrefixes("// REGION BEFORE: "))
 
-            CommandProcessor.getInstance()?.executeCommand(fixture.project,
-                                                           KotlinImportOptimizer().processFile(fixture.file),
-                                                           "Optimize Imports", null,
-                                                           UndoConfirmationPolicy.DO_NOT_REQUEST_CONFIRMATION)
+            fixture.project.executeWriteCommand(
+                "Optimize import in tests"
+            ) { KotlinImportOptimizer().processFile(fixture.file).run() }
+
             getFoldingRegion(0).checkRegion(false, findStringWithPrefixes("// REGION AFTER: "))
+
             null
         }
     }