Add a new option to CompilerOptions to set the value of the $jscomp.ASSUME_ES6

PiperOrigin-RevId: 707308589

Author: Dustyn Loyda

src/com/google/javascript/jscomp/CompilerOptions.java

@@ -183,6 +183,7 @@ void setDependentValuesFromYear(CompilerOptions options) {
       options.languageOutIsDefaultStrict = Optional.of(true);
       options.setDefineToNumberLiteral("goog.FEATURESET_YEAR", year);
       options.setDefineToBooleanLiteral("$jscomp.ASSUME_ES5", year > 2012);
+      options.setDefineToBooleanLiteral("$jscomp.ASSUME_ES6", year > 2018);
     }
 
     FeatureSet getFeatureSet() {

src/com/google/javascript/jscomp/ProcessDefines.java

@@ -59,6 +59,7 @@ class ProcessDefines implements CompilerPass {
           "COMPILED",
           "goog.DEBUG",
           "$jscomp.ASSUME_ES5",
+          "$jscomp.ASSUME_ES6",
           "$jscomp.ISOLATE_POLYFILLS",
           "$jscomp.INSTRUMENT_ASYNC_CONTEXT");
 

test/com/google/javascript/jscomp/CompilerOptionsTest.java

@@ -75,6 +75,17 @@ public void testBrowserFeaturesetYearOptionSetsAssumeES5() {
         .isEqualTo(Token.TRUE);
   }
 
+  @Test
+  public void testBrowserFeaturesetYearOptionSetsAssumeES6() {
+    CompilerOptions options = new CompilerOptions();
+    options.setBrowserFeaturesetYear(2018);
+    assertThat(options.getDefineReplacements().get("$jscomp.ASSUME_ES6").getToken())
+        .isEqualTo(Token.FALSE);
+    options.setBrowserFeaturesetYear(2019);
+    assertThat(options.getDefineReplacements().get("$jscomp.ASSUME_ES6").getToken())
+        .isEqualTo(Token.TRUE);
+  }
+
   @Test
   public void testMinimumBrowserFeatureSetYearRequiredFor() {
     assertThat(BrowserFeaturesetYear.minimumRequiredFor(Feature.GETTER))