Do not run unused symbol inspection if declaration in used in more than 3 scripts

idea/idea-analysis/src/org/jetbrains/kotlin/idea/search/searchUtil.kt

@@ -19,18 +19,27 @@ package org.jetbrains.kotlin.idea.search
 import com.intellij.openapi.fileTypes.FileType
 import com.intellij.openapi.fileTypes.FileTypeRegistry
 import com.intellij.openapi.progress.ProgressIndicator
+import com.intellij.openapi.progress.ProgressManager
 import com.intellij.openapi.project.Project
+import com.intellij.openapi.roots.FileIndexFacade
+import com.intellij.openapi.vfs.VirtualFile
 import com.intellij.psi.PsiElement
 import com.intellij.psi.PsiFile
+import com.intellij.psi.impl.cache.impl.id.IdIndex
+import com.intellij.psi.impl.cache.impl.id.IdIndexEntry
 import com.intellij.psi.search.GlobalSearchScope
 import com.intellij.psi.search.LocalSearchScope
 import com.intellij.psi.search.PsiSearchHelper
 import com.intellij.psi.search.SearchScope
 import com.intellij.psi.search.searches.ReferencesSearch
+import com.intellij.util.Processor
+import com.intellij.util.indexing.FileBasedIndex
 import org.jetbrains.kotlin.idea.KotlinFileType
 import org.jetbrains.kotlin.idea.util.compat.psiSearchHelperInstance
+import org.jetbrains.kotlin.idea.util.application.runReadAction
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi.KtFile
+import org.jetbrains.kotlin.script.findScriptDefinition
 import org.jetbrains.kotlin.types.expressions.OperatorConventions
 
 infix fun SearchScope.and(otherScope: SearchScope): SearchScope = intersectWith(otherScope)
@@ -108,7 +117,36 @@ fun PsiSearchHelper.isCheapEnoughToSearchConsideringOperators(
     fileToIgnoreOccurrencesIn: PsiFile?,
     progress: ProgressIndicator?
 ): PsiSearchHelper.SearchCostResult {
-    if (OperatorConventions.isConventionName(Name.identifier(name))) return PsiSearchHelper.SearchCostResult.TOO_MANY_OCCURRENCES
+    if (OperatorConventions.isConventionName(Name.identifier(name))) {
+        return PsiSearchHelper.SearchCostResult.TOO_MANY_OCCURRENCES
+    }
+
+    if (!isCheapToSearchUsagesInScripts(scope.restrictToKotlinSources(), name)) {
+        return PsiSearchHelper.SearchCostResult.TOO_MANY_OCCURRENCES
+    }
 
     return isCheapEnoughToSearch(name, scope, fileToIgnoreOccurrencesIn, progress)
 }
+
+private fun isCheapToSearchUsagesInScripts(scope: GlobalSearchScope, name: String): Boolean {
+    val project = scope.project ?: return true
+
+    var scriptsCount = 0
+    val processor = object : Processor<VirtualFile> {
+        override fun process(file: VirtualFile): Boolean {
+            ProgressManager.checkCanceled()
+            if (findScriptDefinition(file, project) == null) return true
+            return scriptsCount++ < 3
+        }
+    }
+
+    val index = FileIndexFacade.getInstance(project)
+    return runReadAction {
+        FileBasedIndex.getInstance().processFilesContainingAllKeys(
+            IdIndex.NAME,
+            listOf(IdIndexEntry(name, true)),
+            scope,
+            null,
+            { file -> !index.shouldBeFound(scope, file) || processor.process(file) })
+    }
+}

idea/src/org/jetbrains/kotlin/idea/inspections/UnusedSymbolInspection.kt

@@ -24,6 +24,7 @@ import com.intellij.psi.PsiElement
 import com.intellij.psi.PsiElementVisitor
 import com.intellij.psi.PsiReference
 import com.intellij.psi.search.GlobalSearchScope
+import com.intellij.psi.search.PsiSearchHelper.SearchCostResult
 import com.intellij.psi.search.PsiSearchHelper.SearchCostResult.*
 import com.intellij.psi.search.SearchScope
 import com.intellij.psi.search.searches.DefinitionsScopedSearch
@@ -109,7 +110,34 @@ class UnusedSymbolInspection : AbstractKotlinInspection() {
                 }
                 else -> return false
             }
-            return lightElement != null && javaInspection.isEntryPoint(lightElement)
+
+            if (lightElement == null) return false
+
+            if (isCheapEnoughToSearchUsages(declaration) == TOO_MANY_OCCURRENCES) return false
+
+            return javaInspection.isEntryPoint(lightElement)
+        }
+
+        private fun isCheapEnoughToSearchUsages(declaration: KtNamedDeclaration): SearchCostResult {
+            val project = declaration.project
+            val psiSearchHelper = psiSearchHelperInstance(project)
+
+            val useScope = psiSearchHelper.getUseScope(declaration)
+            if (useScope is GlobalSearchScope) {
+                var zeroOccurrences = true
+                for (name in listOf(declaration.name) + declaration.getAccessorNames() + listOfNotNull(declaration.getClassNameForCompanionObject())) {
+                    if (name == null) continue
+                    when (psiSearchHelper.isCheapEnoughToSearchConsideringOperators(name, useScope, null, null)) {
+                        ZERO_OCCURRENCES -> {
+                        } // go on, check other names
+                        FEW_OCCURRENCES -> zeroOccurrences = false
+                        TOO_MANY_OCCURRENCES -> return TOO_MANY_OCCURRENCES // searching usages is too expensive; behave like it is used
+                    }
+                }
+
+                if (zeroOccurrences) return ZERO_OCCURRENCES
+            }
+            return FEW_OCCURRENCES
         }
 
         private fun KtProperty.isSerializationImplicitlyUsedField(): Boolean {
@@ -223,18 +251,13 @@ class UnusedSymbolInspection : AbstractKotlinInspection() {
         val project = declaration.project
         val psiSearchHelper = psiSearchHelperInstance(project)
 
-        val useScope = declaration.useScope
+        val useScope = psiSearchHelper.getUseScope(declaration)
         val restrictedScope = if (useScope is GlobalSearchScope) {
-            var zeroOccurrences = true
+            val enoughToSearchUsages = isCheapEnoughToSearchUsages(declaration)
-
+            val zeroOccurrences = when (enoughToSearchUsages) {
-            for (name in listOf(declaration.name) + declaration.getAccessorNames() + listOfNotNull(declaration.getClassNameForCompanionObject())) {
+                ZERO_OCCURRENCES -> true
-                if (name == null) continue
+                FEW_OCCURRENCES -> false
-                when (psiSearchHelper.isCheapEnoughToSearchConsideringOperators(name, useScope, null, null)) {
+                TOO_MANY_OCCURRENCES -> return true // searching usages is too expensive; behave like it is used
-                    ZERO_OCCURRENCES -> {
-                    } // go on, check other names
-                    FEW_OCCURRENCES -> zeroOccurrences = false
-                    TOO_MANY_OCCURRENCES -> return true // searching usages is too expensive; behave like it is used
-                }
             }
 
             if (zeroOccurrences && !declaration.hasActualModifier()) {