Allow typescript keywords in import and export statements

Default behavior forbids the use of TypeScript keywords in import and export statements: modify scanner to emit IdentifierTokens when parseTypeSyntax is false.

Export decl parser coerces identifiers in exports to keywords: check there also.

Addresses google#2005

Closes google#2835

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=188511416

src/com/google/javascript/jscomp/parsing/parser/Parser.java

@@ -194,7 +194,8 @@ public Parser(
       boolean initialGeneratorContext) {
     this.config = config;
     this.errorReporter = errorReporter;
-    this.scanner = new Scanner(errorReporter, commentRecorder, source, offset);
+    this.scanner =
+        new Scanner(config.parseTypeSyntax, errorReporter, commentRecorder, source, offset);
     this.functionContextStack.addLast(
         initialGeneratorContext ? FunctionFlavor.GENERATOR : FunctionFlavor.NORMAL);
     lastSourcePosition = scanner.getPosition();
@@ -278,6 +279,12 @@ public String getSourceMapURL() {
     return sourceMapURL;
   }
 
+  /** Returns true if the string value should be treated as a keyword in the current context. */
+  private boolean isKeyword(String value) {
+    return Keywords.isKeyword(value)
+        && (!Keywords.isTypeScriptSpecificKeyword(value) || config.parseTypeSyntax);
+  }
+
   // 14 Program
   public ProgramTree parseProgram() {
     Timer t = new Timer("Parse Program");
@@ -459,7 +466,7 @@ private ParseTree parseImportSpecifier() {
     if (peekPredefinedString(PredefinedName.AS)) {
       eatPredefinedString(PredefinedName.AS);
       destinationName = eatId();
-    } else if (Keywords.isKeyword(importedName.value)) {
+    } else if (isKeyword(importedName.value)) {
       reportExpectedError(null, PredefinedName.AS);
     }
     return new ImportSpecifierTree(
@@ -565,7 +572,7 @@ private ParseTree parseExportDeclaration(boolean isAmbient) {
     } else if (isExportSpecifier) {
       for (ParseTree tree : exportSpecifierList) {
         IdentifierToken importedName = tree.asExportSpecifier().importedName;
-        if (Keywords.isKeyword(importedName.value)) {
+        if (isKeyword(importedName.value)) {
           reportError(importedName, "cannot use keyword '%s' here.", importedName.value);
         }
       }

src/com/google/javascript/jscomp/parsing/parser/Scanner.java

@@ -32,20 +32,29 @@
  * <p>7 Lexical Conventions
  */
 public class Scanner {
+  private final boolean parseTypeSyntax;
   private final ErrorReporter errorReporter;
   private final SourceFile source;
   private final ArrayList<Token> currentTokens = new ArrayList<>();
   private int index;
   private final CommentRecorder commentRecorder;
   private int typeParameterLevel;
 
-  public Scanner(ErrorReporter errorReporter, CommentRecorder commentRecorder,
+  public Scanner(
+      boolean parseTypeSyntax,
+      ErrorReporter errorReporter,
+      CommentRecorder commentRecorder,
       SourceFile source) {
-    this(errorReporter, commentRecorder, source, 0);
+    this(parseTypeSyntax, errorReporter, commentRecorder, source, 0);
   }
 
-  public Scanner(ErrorReporter errorReporter, CommentRecorder commentRecorder,
-      SourceFile file, int offset) {
+  public Scanner(
+      boolean parseTypeSyntax,
+      ErrorReporter errorReporter,
+      CommentRecorder commentRecorder,
+      SourceFile file,
+      int offset) {
+    this.parseTypeSyntax = parseTypeSyntax;
     this.errorReporter = errorReporter;
     this.commentRecorder = commentRecorder;
     this.source = file;
@@ -725,7 +734,7 @@ private Token scanIdentifierOrKeyword(int beginToken, char ch) {
     }
 
     Keywords k = Keywords.get(value);
-    if (k != null) {
+    if (k != null && (!Keywords.isTypeScriptSpecificKeyword(value) || parseTypeSyntax)) {
       return new Token(k.type, getTokenRange(beginToken));
     }
 

test/com/google/javascript/jscomp/parsing/ParserTest.java

@@ -3657,6 +3657,15 @@ public void testExport() {
     parseError("export * as s from './someModule';", "'from' expected");
   }
 
+  public void testImportExportTypescriptKeyword() {
+    mode = LanguageMode.TYPESCRIPT;
+    parseError("export { namespace };", "cannot use keyword 'namespace' here.");
+
+    mode = LanguageMode.ECMASCRIPT6;
+    parse("export { namespace };");
+    parse("import { namespace } from './input0.js';");
+  }
+
   public void testGoogModule() {
     Node tree = parse("goog.module('example');");
     assertNode(tree).hasType(Token.SCRIPT);

test/com/google/javascript/jscomp/parsing/TypeSyntaxTest.java

@@ -537,7 +537,7 @@ public void testTypeAlias() {
     expectErrors("Parse error. Semi-colon expected");
     parse("if (true) { type Foo = number; }");
 
-    testNotEs6Typed("type Foo = number;", "type alias");
+    testNotEs6TypedFullError("type Foo = number;", "Parse error. Semi-colon expected");
   }
 
   public void testAmbientDeclaration() {
@@ -566,7 +566,8 @@ public void testAmbientDeclaration() {
     expectErrors("Parse error. Semi-colon expected");
     parse("declare class Foo {\n  constructor() {}\n};");
 
-    testNotEs6Typed("declare var x;", "ambient declaration");
+    testNotEs6TypedFullError("declare var x;", "Parse error. Semi-colon expected");
+
   }
 
   public void testExportDeclaration() {
@@ -728,7 +729,7 @@ public void testNamespace() {
     expectErrors("Parse error. Semi-colon expected");
     parse("namespace 'foo' {}"); // External modules are not supported
 
-    testNotEs6Typed("namespace foo {}", "namespace declaration");
+    testNotEs6TypedFullError("namespace foo {}", "Parse error. Semi-colon expected");
   }
 
   public void testAmbientNameSpace() {
@@ -765,7 +766,7 @@ public void testAmbientNameSpace() {
     expectErrors("Parse error. '}' expected");
     parse("declare namespace foo { type Foo = number; }");
 
-    testNotEs6Typed("declare namespace foo {}", "ambient declaration", "namespace declaration");
+    testNotEs6TypedFullError("declare namespace foo {}", "Parse error. Semi-colon expected");
   }
 
   private void assertVarType(String message, TypeDeclarationNode expectedType, String source) {