JS: optimize default arguments in cross-module inliner

This reduces size of circlet UI (of approx 2.5 mb) by about 90 kb

js/js.inliner/src/org/jetbrains/kotlin/js/inline/FunctionReader.kt

@@ -30,6 +30,7 @@ import org.jetbrains.kotlin.js.parser.parseFunction
 import org.jetbrains.kotlin.js.parser.sourcemaps.*
 import org.jetbrains.kotlin.js.translate.context.Namer
 import org.jetbrains.kotlin.js.translate.expression.InlineMetadata
+import org.jetbrains.kotlin.js.translate.utils.JsAstUtils
 import org.jetbrains.kotlin.js.translate.utils.JsDescriptorUtils.getModuleName
 import org.jetbrains.kotlin.resolve.descriptorUtil.isExtension
 import org.jetbrains.kotlin.resolve.inline.InlineStrategy
@@ -243,6 +244,7 @@ class FunctionReader(
         replaceExternalNames(function, replacements, allDefinedNames)
         wrapperStatements?.forEach { replaceExternalNames(it, replacements, allDefinedNames) }
         function.markInlineArguments(descriptor)
+        markDefaultParams(function)
 
         info.wrapFunctionVariable.let { wrapFunction ->
             for (externalName in (collectReferencedNames(function) - allDefinedNames).filter { it.ident == wrapFunction }) {
@@ -270,6 +272,26 @@ class FunctionReader(
 
         return FunctionWithWrapper(function, wrapper)
     }
+
+    private fun markDefaultParams(function: JsFunction) {
+        val paramsByNames = function.parameters.associate { it.name to it }
+        for (ifStatement in function.body.statements) {
+            if (ifStatement !is JsIf || ifStatement.elseStatement != null) break
+            val thenStatement = ifStatement.thenStatement as? JsExpressionStatement ?: break
+            val testExpression = ifStatement.ifExpression as? JsBinaryOperation ?: break
+
+            if (testExpression.operator != JsBinaryOperator.REF_EQ) break
+            val testLhs = testExpression.arg1 as? JsNameRef ?: break
+            val param = paramsByNames[testLhs.name] ?: break
+            if (testLhs.qualifier != null) break
+            if ((testExpression.arg2 as? JsPrefixOperation)?.operator != JsUnaryOperator.VOID) break
+
+            val (assignLhs) = JsAstUtils.decomposeAssignmentToVariable(thenStatement.expression) ?: break
+            if (assignLhs != testLhs.name) break
+
+            param.hasDefaultValue = true
+        }
+    }
 }
 
 private val Char.isWhitespaceOrComma: Boolean

js/js.inliner/src/org/jetbrains/kotlin/js/inline/util/namingUtils.kt

@@ -21,6 +21,7 @@ import org.jetbrains.kotlin.js.backend.ast.metadata.staticRef
 
 import org.jetbrains.kotlin.js.inline.context.NamingContext
 import org.jetbrains.kotlin.js.inline.util.rewriters.LabelNameRefreshingVisitor
+import org.jetbrains.kotlin.js.translate.utils.JsAstUtils
 
 fun aliasArgumentsIfNeeded(
         context: NamingContext,
@@ -30,7 +31,12 @@ fun aliasArgumentsIfNeeded(
 ) {
     require(arguments.size <= parameters.size) { "arguments.size (${arguments.size}) should be less or equal to parameters.size (${parameters.size})" }
 
+    val defaultParams = mutableListOf<JsParameter>()
     for ((arg, param) in arguments.zip(parameters)) {
+        if (JsAstUtils.isUndefinedExpression(arg)) {
+            defaultParams += param
+            continue
+        }
         val paramName = param.name
 
         val replacement = JsScope.declareTemporaryName(paramName.ident).apply {
@@ -42,7 +48,7 @@ fun aliasArgumentsIfNeeded(
         context.replaceName(paramName, replacement)
     }
 
-    val defaultParams = parameters.subList(arguments.size, parameters.size)
+    defaultParams += parameters.subList(arguments.size, parameters.size)
     for (defaultParam in defaultParams) {
         val paramName = defaultParam.name
         val freshName = JsScope.declareTemporaryName(paramName.ident)

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/BoxJsTestGenerated.java

@@ -5096,6 +5096,12 @@ public class BoxJsTestGenerated extends AbstractBoxJsTest {
             doTest(fileName);
         }
 
+        @TestMetadata("multiModuleDefaultArgsCleanup.kt")
+        public void testMultiModuleDefaultArgsCleanup() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/inlineSizeReduction/multiModuleDefaultArgsCleanup.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("noDuplicateVariableDeclaration.kt")
         public void testNoDuplicateVariableDeclaration() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/inlineSizeReduction/noDuplicateVariableDeclaration.kt");

js/js.translator/testData/box/inlineSizeReduction/multiModuleDefaultArgsCleanup.kt

@@ -0,0 +1,17 @@
+// EXPECTED_REACHABLE_NODES: 1018
+// MODULE: lib
+// FILE: lib.kt
+inline fun foo(x: String = "x", y: String = "y") = x + y
+
+// MODULE: main(lib)
+// FILE: main.kt
+// CHECK_VARS_COUNT: function=test count=0
+
+fun test() = foo() + ";" + foo(x = "X") + ";" + foo(y = "Y") + ";" + foo(x = "X", y = "Y")
+
+fun box(): String {
+    val r = test()
+    if (test() != "xy;Xy;xY;XY") return "fail: $r"
+
+    return "OK"
+}