Add the ASSUME_ES2020 compiler define and use it to simplify "$jscomp.global"

Also Update the option handler to set ASSUME_ES6 and ASSUME_ES2020 when appropriate.

PiperOrigin-RevId: 715927528

Author: concavelenz

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

@@ -185,7 +185,8 @@ 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);
+      options.setDefineToBooleanLiteral("$jscomp.ASSUME_ES6", year >= 2018);
+      options.setDefineToBooleanLiteral("$jscomp.ASSUME_ES2020", year >= 2021);
     }
 
     FeatureSet getFeatureSet() {

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

@@ -60,6 +60,7 @@ class ProcessDefines implements CompilerPass {
           "goog.DEBUG",
           "$jscomp.ASSUME_ES5",
           "$jscomp.ASSUME_ES6",
+          "$jscomp.ASSUME_ES2020",
           "$jscomp.ISOLATE_POLYFILLS",
           "$jscomp.INSTRUMENT_ASYNC_CONTEXT");
 

src/com/google/javascript/jscomp/js/util/defines.js

@@ -31,6 +31,15 @@ $jscomp.ASSUME_ES5 = false;
  */
 $jscomp.ASSUME_ES6 = false;
 
+/**
+ * Whether to assume ES2020 is available.  This enables removing several
+ * internal polyfills, which must otherwise be detected at runtime.
+ * @define {boolean}
+ */
+$jscomp.ASSUME_ES2020 = false;
+
+
+
 /**
  * Whether to skip the conformance check and simply use the polyfill always.
  * @define {boolean}

src/com/google/javascript/jscomp/js/util/global.js

@@ -19,6 +19,7 @@
  * @suppress {uselessCode}
  */
 'require base';
+'require util/defines';
 
 /**
  * Locate and return a reference to the global object.
@@ -85,4 +86,4 @@ $jscomp.getGlobal = function(passedInThis) {
  * The global object.
  * @const {!Global}
  */
-$jscomp.global = $jscomp.getGlobal(this);
+$jscomp.global = $jscomp.ASSUME_ES2020 ? globalThis : $jscomp.getGlobal(this);

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

@@ -81,12 +81,18 @@ public void testBrowserFeaturesetYearOptionSetsAssumeES5() {
   @Test
   public void testBrowserFeaturesetYearOptionSetsAssumeES6() {
     CompilerOptions options = new CompilerOptions();
-    options.setBrowserFeaturesetYear(2018);
+    options.setBrowserFeaturesetYear(2012);
     assertThat(options.getDefineReplacements().get("$jscomp.ASSUME_ES6").getToken())
         .isEqualTo(Token.FALSE);
-    options.setBrowserFeaturesetYear(2019);
+    options.setBrowserFeaturesetYear(2018);
     assertThat(options.getDefineReplacements().get("$jscomp.ASSUME_ES6").getToken())
         .isEqualTo(Token.TRUE);
+    options.setBrowserFeaturesetYear(2020);
+    assertThat(options.getDefineReplacements().get("$jscomp.ASSUME_ES2020").getToken())
+        .isEqualTo(Token.FALSE);
+    options.setBrowserFeaturesetYear(2021);
+    assertThat(options.getDefineReplacements().get("$jscomp.ASSUME_ES2020").getToken())
+        .isEqualTo(Token.TRUE);
   }
 
   @Test

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

@@ -113,10 +113,10 @@ public void testInjection_doesntCrashOnLibrariesWithCasts_ifTypecheckingHasNotRu
 
     ImmutableList<Node> objectNameNodes =
         findNodesNamed(this.getLastCompiler().getRoot(), "globalThis");
-    assertThat(objectNameNodes).hasSize(3);
+    assertThat(objectNameNodes).hasSize(4);
 
     Node injectedGlobalThisNode = objectNameNodes.get(0);
-    Node sourceGlobalThisNode = objectNameNodes.get(2);
+    Node sourceGlobalThisNode = objectNameNodes.get(3);
 
     assertThat(injectedGlobalThisNode.getSourceFileName()).contains("util/global");
     assertThat(sourceGlobalThisNode.getSourceFileName()).contains("testcode");