JS DCE: disable logging by default

Based on Vladislav Saifulin's PR #4031

js/js.dce/src/org/jetbrains/kotlin/js/dce/DeadCodeElimination.kt

@@ -38,7 +38,10 @@ import org.jetbrains.kotlin.js.util.TextOutputImpl
 import java.io.File
 import java.io.InputStreamReader
 
-class DeadCodeElimination(private val logConsumer: (DCELogLevel, String) -> Unit) {
+class DeadCodeElimination(
+    private val printReachabilityInfo: Boolean,
+    private val logConsumer: (DCELogLevel, String) -> Unit
+) {
     val moduleMapping = mutableMapOf<JsBlock, String>()
     private val reachableNames = mutableSetOf<String>()
 
@@ -61,7 +64,7 @@ class DeadCodeElimination(private val logConsumer: (DCELogLevel, String) -> Unit
         analyzer.moduleMapping += moduleMapping
         root.accept(analyzer)
 
-        val usageFinder = ReachabilityTracker(context, analyzer.analysisResult, logConsumer)
+        val usageFinder = ReachabilityTracker(context, analyzer.analysisResult, logConsumer.takeIf { printReachabilityInfo })
         root.accept(usageFinder)
 
         for (reachableName in reachableNames) {
@@ -78,10 +81,11 @@ class DeadCodeElimination(private val logConsumer: (DCELogLevel, String) -> Unit
         fun run(
                 inputFiles: Collection<InputFile>,
                 rootReachableNames: Set<String>,
+                printReachabilityInfo: Boolean,
                 logConsumer: (DCELogLevel, String) -> Unit
         ): DeadCodeEliminationResult {
             val program = JsProgram()
-            val dce = DeadCodeElimination(logConsumer)
+            val dce = DeadCodeElimination(printReachabilityInfo, logConsumer)
 
             var hasErrors = false
             val blocks = inputFiles.map { file ->

js/js.dce/src/org/jetbrains/kotlin/js/dce/ReachabilityTracker.kt

@@ -23,7 +23,7 @@ import org.jetbrains.kotlin.js.inline.util.collectLocalVariables
 class ReachabilityTracker(
         private val context: Context,
         private val analysisResult: AnalysisResult,
-        private val logConsumer: (DCELogLevel, String) -> Unit
+        private val logConsumer: ((DCELogLevel, String) -> Unit)?
 ) : RecursiveJsVisitor() {
     companion object {
         private val CALL_FUNCTIONS = setOf("call", "apply")
@@ -237,14 +237,15 @@ class ReachabilityTracker(
         currentNodeWithLocation = old
     }
 
-    private fun report(message: String) {
-        logConsumer(DCELogLevel.INFO, "  ".repeat(depth) + message)
-    }
-
     private fun reportAndNest(message: String, dueTo: JsNode?, action: () -> Unit) {
-        val location = dueTo?.extractLocation()
-        val fullMessage = if (location != null) "$message (due to ${location.asString()})" else message
-        report(fullMessage)
+        if (logConsumer != null) {
+            val indent = "  ".repeat(depth)
+            val fullMessage = when (val location = dueTo?.extractLocation()) {
+                null -> "$indent$message"
+                else -> "$indent$message (due to ${location.asString()})"
+            }
+            logConsumer.invoke(DCELogLevel.INFO, fullMessage)
+        }
         nested(action)
     }