feat(Escaped Identifiers): add ability to use any symbol wrapped in back ticks.

js/js.frontend/src/org/jetbrains/kotlin/js/naming/NameSuggestion.kt

@@ -19,6 +19,8 @@ package org.jetbrains.kotlin.js.naming
 import org.jetbrains.kotlin.builtins.ReflectionTypes
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.impl.TypeAliasConstructorDescriptor
+import org.jetbrains.kotlin.js.common.isES5IdentifierPart
+import org.jetbrains.kotlin.js.common.isES5IdentifierStart
 import org.jetbrains.kotlin.js.translate.utils.AnnotationsUtils.getNameForAnnotatedObject
 import org.jetbrains.kotlin.js.translate.utils.AnnotationsUtils.isNativeObject
 import org.jetbrains.kotlin.name.Name
@@ -358,55 +360,4 @@ class NameSuggestion {
             return first.toString() + name.drop(1).map { if (it.isES5IdentifierPart()) it else '_' }.joinToString("")
         }
     }
-}
-
-private fun Char.isAllowedLatinLetterOrSpecial(): Boolean {
-    return this in 'a'..'z' || this in 'A'..'Z' || this == '_' || this == '$'
-}
-
-private fun Char.isAllowedSimpleDigit() =
-    this in '0'..'9'
-
-private fun Char.isNotAllowedSimpleCharacter() = when (this) {
-    ' ', '<', '>', '-', '?' -> true
-    else -> false
-}
-
-fun Char.isES5IdentifierStart(): Boolean {
-    if (isAllowedLatinLetterOrSpecial()) return true
-    if (isNotAllowedSimpleCharacter()) return false
-
-    return isES5IdentifierStartFull()
-}
-
-// See ES 5.1 spec: https://www.ecma-international.org/ecma-262/5.1/#sec-7.6
-private fun Char.isES5IdentifierStartFull() =
-    Character.isLetter(this) ||   // Lu | Ll | Lt | Lm | Lo
-            // Nl which is missing in Character.isLetter, but present in UnicodeLetter in spec
-            Character.getType(this).toByte() == Character.LETTER_NUMBER
-
-
-fun Char.isES5IdentifierPart(): Boolean {
-    if (isAllowedLatinLetterOrSpecial()) return true
-    if (isAllowedSimpleDigit()) return true
-    if (isNotAllowedSimpleCharacter()) return false
-
-    return isES5IdentifierStartFull() ||
-            when (Character.getType(this).toByte()) {
-                Character.NON_SPACING_MARK,
-                Character.COMBINING_SPACING_MARK,
-                Character.DECIMAL_DIGIT_NUMBER,
-                Character.CONNECTOR_PUNCTUATION -> true
-                else -> false
-            } ||
-            this == '\u200C' ||   // Zero-width non-joiner
-            this == '\u200D'      // Zero-width joiner
-}
-
-fun String.isValidES5Identifier(): Boolean {
-    if (isEmpty() || !this[0].isES5IdentifierStart()) return false
-    for (idx in 1 ..length-1) {
-        if (!get(idx).isES5IdentifierPart()) return false
-    }
-    return true
 }

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/JsPlatformConfigurator.kt

@@ -17,28 +17,28 @@ import org.jetbrains.kotlin.resolve.checkers.ExpectedActualDeclarationChecker
 import org.jetbrains.kotlin.types.DynamicTypesAllowed
 
 object JsPlatformConfigurator : PlatformConfiguratorBase(
-        DynamicTypesAllowed(),
-        additionalDeclarationCheckers = listOf(
-            NativeInvokeChecker(), NativeGetterChecker(), NativeSetterChecker(),
-            JsNameChecker, JsModuleChecker, JsExternalFileChecker,
-            JsExternalChecker, JsInheritanceChecker, JsMultipleInheritanceChecker,
-            JsRuntimeAnnotationChecker,
-            JsDynamicDeclarationChecker,
-            JsExportAnnotationChecker,
-            JsExportDeclarationChecker
-        ),
-        additionalCallCheckers = listOf(
-            JsModuleCallChecker,
-            JsDynamicCallChecker,
-            JsDefinedExternallyCallChecker,
-        ),
-        identifierChecker = JsIdentifierChecker
+    DynamicTypesAllowed(),
+    additionalDeclarationCheckers = listOf(
+        NativeInvokeChecker(), NativeGetterChecker(), NativeSetterChecker(),
+        JsNameChecker, JsModuleChecker, JsExternalFileChecker,
+        JsExternalChecker, JsInheritanceChecker, JsMultipleInheritanceChecker,
+        JsRuntimeAnnotationChecker,
+        JsDynamicDeclarationChecker,
+        JsExportAnnotationChecker,
+        JsExportDeclarationChecker
+    ),
+    additionalCallCheckers = listOf(
+        JsModuleCallChecker,
+        JsDynamicCallChecker,
+        JsDefinedExternallyCallChecker,
+    ),
 ) {
     override fun configureModuleComponents(container: StorageComponentContainer) {
         container.useInstance(NameSuggestion())
         container.useImpl<JsCallChecker>()
         container.useImpl<JsTypeSpecificityComparator>()
         container.useImpl<JsNameClashChecker>()
+        container.useImpl<JsIdentifierChecker>()
         container.useImpl<JsNameCharsChecker>()
         container.useImpl<JsBuiltinNameClashChecker>()
         container.useInstance(JsModuleClassLiteralChecker)

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsDynamicCallChecker.kt

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.js.resolve.diagnostics
 
 import com.intellij.psi.PsiElement
+import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.js.naming.NameSuggestion
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.*
@@ -82,7 +83,9 @@ object JsDynamicCallChecker : CallChecker {
     }
 
     private fun checkIdentifier(name: String?, reportOn: PsiElement, context: CallCheckerContext) {
-        if (name == null) return
+        if (name == null || context.languageVersionSettings.supportsFeature(LanguageFeature.JsAllowInvalidCharsIdentifiersEscaping)) {
+            return
+        }
         if (NameSuggestion.sanitizeName(name) != name) {
             context.trace.report(ErrorsJs.NAME_CONTAINS_ILLEGAL_CHARS.on(reportOn))
         }

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsIdentifierChecker.kt

@@ -16,6 +16,8 @@
 
 package org.jetbrains.kotlin.js.resolve.diagnostics
 
+import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.diagnostics.DiagnosticSink
 import org.jetbrains.kotlin.diagnostics.Errors
 import org.jetbrains.kotlin.js.naming.NameSuggestion
@@ -23,8 +25,11 @@ import org.jetbrains.kotlin.psi.KtDeclaration
 import org.jetbrains.kotlin.psi.KtSimpleNameExpression
 import org.jetbrains.kotlin.resolve.IdentifierChecker
 
-object JsIdentifierChecker : IdentifierChecker {
+class JsIdentifierChecker(private val languageVersionSettings: LanguageVersionSettings) : IdentifierChecker {
     override fun checkIdentifier(simpleNameExpression: KtSimpleNameExpression, diagnosticHolder: DiagnosticSink) {
+        if (languageVersionSettings.supportsFeature(LanguageFeature.JsAllowInvalidCharsIdentifiersEscaping)) {
+            return
+        }
         val simpleName = simpleNameExpression.getReferencedName()
 
         val hasIllegalChars = simpleName.split('.').any { NameSuggestion.sanitizeName(it) != it }

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsNameCharsChecker.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.js.resolve.diagnostics
 
+import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.ConstructorDescriptor
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 import org.jetbrains.kotlin.descriptors.PropertyAccessorDescriptor
@@ -16,6 +17,9 @@ import org.jetbrains.kotlin.resolve.checkers.DeclarationCheckerContext
 
 class JsNameCharsChecker(private val suggestion: NameSuggestion) : DeclarationChecker {
     override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+        if (context.languageVersionSettings.supportsFeature(LanguageFeature.JsAllowInvalidCharsIdentifiersEscaping)) {
+            return
+        }
         val bindingContext = context.trace.bindingContext
 
         if (descriptor is PropertyAccessorDescriptor && AnnotationsUtils.getJsName(descriptor) == null) return