Add -keep command line option to JS DCE tool

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JSDceArguments.kt

@@ -26,6 +26,13 @@ class K2JSDceArguments : CommonToolArguments() {
     @JvmField
     var outputDirectory: String? = null
 
+    @field:Argument(
+            value = "-keep",
+            valueDescription = "<fully.qualified.name[,]>",
+            description = "List of fully-qualified names of declarations that shouldn't be eliminated")
+    @JvmField
+    var declarationsToKeep: Array<String>? = null
+
     @field:GradleOption(DefaultValues.BooleanFalseDefault::class)
     @field:Argument(value = "-Xprint-reachability-info", description = "Print declarations marked as reachable")
     @JvmField

compiler/cli/src/org/jetbrains/kotlin/cli/js/dce/K2JSDce.kt

@@ -49,7 +49,9 @@ class K2JSDce : CLITool<K2JSDceArguments>() {
             return ExitCode.COMPILATION_ERROR
         }
 
-        val dceResult = DeadCodeElimination.run(files, emptySet()) {
+        val includedDeclarations = arguments.declarationsToKeep.orEmpty().toSet()
+
+        val dceResult = DeadCodeElimination.run(files, includedDeclarations) {
             messageCollector.report(CompilerMessageSeverity.LOGGING, it)
         }
         val nodes = dceResult.reachableNodes

compiler/testData/cli/js-dce/dceHelp.out

@@ -1,6 +1,8 @@
 Usage: kotlin-dce-js <options> <source files>
 where possible options include:
   -output-dir <path>         Output directory
+  -keep <fully.qualified.name[,]>
+                             List of fully-qualified names of declarations that shouldn't be eliminated
   -help (-h)                 Print a synopsis of standard options
   -X                         Print a synopsis of advanced options
   -version                   Display compiler version

compiler/testData/cli/js-dce/include.js

@@ -0,0 +1,20 @@
+define(["exports"], function(exports) {
+    function foo() {
+    }
+
+    function bar() {
+    }
+
+    function baz() {
+    }
+
+    function ignore() {
+    }
+
+    baz();
+
+    exports.foo = foo;
+    exports.bar = bar;
+    exports.baz = baz;
+    exports.ignore = ignore;
+});

compiler/testData/cli/js-dce/includeDeclarations.args

@@ -0,0 +1,6 @@
+$TESTDATA_DIR$/include.js
+-output-dir
+$TEMP_DIR$/min
+-keep
+global.foo,global.bar
+-Xprint-reachability-info

compiler/tests/org/jetbrains/kotlin/cli/CliTestGenerated.java

@@ -560,6 +560,12 @@ public class CliTestGenerated extends AbstractCliTest {
             doJsDceTest(fileName);
         }
 
+        @TestMetadata("includeDeclarations.args")
+        public void testIncludeDeclarations() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/cli/js-dce/includeDeclarations.args");
+            doJsDceTest(fileName);
+        }
+
         @TestMetadata("jsExtraHelp.args")
         public void testJsExtraHelp() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/cli/js-dce/jsExtraHelp.args");