Base support for coalescing & logical assignment

Base PR for #20531.

Author: RReverser

src/settings.js

@@ -1768,10 +1768,10 @@ var AUTO_NATIVE_LIBRARIES = true;
 // versions >= MIN_FIREFOX_VERSION
 // are desired to work. Pass -sMIN_FIREFOX_VERSION=majorVersion to drop support
 // for Firefox versions older than < majorVersion.
-// Firefox ESR 68 was released on July 9, 2019.
+// Firefox 79 was released on 2020-07-28.
 // MAX_INT (0x7FFFFFFF, or -1) specifies that target is not supported.
 // [link]
-var MIN_FIREFOX_VERSION = 68;
+var MIN_FIREFOX_VERSION = 79;
 
 // Specifies the oldest version of desktop Safari to target. Version is encoded
 // in MMmmVV, e.g. 70101 denotes Safari 7.1.1.
@@ -1810,10 +1810,10 @@ var MIN_EDGE_VERSION = 0x7FFFFFFF;
 
 // Specifies the oldest version of Chrome. E.g. pass -sMIN_CHROME_VERSION=58 to
 // drop support for Chrome 57 and older.
-// Chrome 75.0.3770 was released on 2019-06-04
+// Chrome 85 was released on 2020-08-25.
 // MAX_INT (0x7FFFFFFF, or -1) specifies that target is not supported.
 // [link]
-var MIN_CHROME_VERSION = 75;
+var MIN_CHROME_VERSION = 85;
 
 // Specifies minimum node version to target for the generated code.  This is
 // distinct from the minimum version required run the emscripten compiler.

test/test_other.py

@@ -12966,14 +12966,16 @@ def test_es5_transpile(self, args):
     # - arrow funcs
     # - for..of
     # - object.assign
+    # - nullish coalescing & chaining
+    # - logical assignment
     create_file('es6_library.js', '''\
     addToLibrary({
       foo: function(arg="hello") {
         // Object.assign + let
         let obj = Object.assign({}, {prop:1});
         err('prop: ' + obj.prop);
 
-        // arror funcs + const
+        // arrow funcs + const
         const bar = () => 2;
         err('bar: ' + bar());
 
@@ -12990,6 +12992,22 @@ def test_es5_transpile(self, args):
         };
         global['foo'] = obj3;
         err('value2: ' + obj3.myMethod());
+
+        // Nullish coalescing
+        var definitely = global['maybe'] ?? {};
+
+        // Optional chaining
+        global['maybe']
+          ?.subObj
+          ?.[key]
+          ?.func
+          ?.();
+
+        // Logical assignment
+        var obj4 = null;
+        obj4 ??= 0;
+        obj4 ||= 1;
+        obj4 &&= 2;
       }
     });
     ''')
@@ -13004,13 +13022,22 @@ def check_for_es6(filename, expect):
         self.assertContained(['() => 2', '()=>2'], js)
         self.assertContained('const ', js)
         self.assertContained('let ', js)
+        self.assertContained('?.[', js)
+        self.assertContained('?.(', js)
+        self.assertContained('??=', js)
+        self.assertContained('||=', js)
+        self.assertContained('&&=', js)
       else:
         self.verify_es5(filename)
         self.assertNotContained('foo(arg=', js)
         self.assertNotContained('() => 2', js)
         self.assertNotContained('()=>2', js)
         self.assertNotContained('const ', js)
         self.assertNotContained('let ', js)
+        self.assertNotContained('??', js)
+        self.assertNotContained('?.', js)
+        self.assertNotContained('||=', js)
+        self.assertNotContained('&&=', js)
 
     # Check that under normal circumstances none of these features get
     # removed / transpiled.

tools/acorn-optimizer.js

@@ -1044,7 +1044,7 @@ function applyDCEGraphRemovals(ast) {
 
 // Need a parser to pass to acorn.Node constructor.
 // Create it once and reuse it.
-const stubParser = new acorn.Parser({ecmaVersion: 2020});
+const stubParser = new acorn.Parser({ecmaVersion: 2021});
 
 function createNode(props) {
   const node = new acorn.Node(stubParser);
@@ -2008,7 +2008,7 @@ let ast;
 try {
   ast = acorn.parse(input, {
     // Keep in sync with --language_in that we pass to closure in building.py
-    ecmaVersion: 2020,
+    ecmaVersion: 2021,
     preserveParens: closureFriendly,
     onComment: closureFriendly ? sourceComments : undefined,
     sourceType: exportES6 ? 'module' : 'script',

tools/building.py

@@ -567,7 +567,7 @@ def closure_compiler(filename, advanced=True, extra_closure_args=None):
 
   args = ['--compilation_level', 'ADVANCED_OPTIMIZATIONS' if advanced else 'SIMPLE_OPTIMIZATIONS']
   # Keep in sync with ecmaVersion in tools/acorn-optimizer.js
-  args += ['--language_in', 'ECMASCRIPT_2020']
+  args += ['--language_in', 'ECMASCRIPT_2021']
   # Tell closure not to do any transpiling or inject any polyfills.
   # At some point we may want to look into using this as way to convert to ES5 but
   # babel is perhaps a better tool for that.

tools/unsafe_optimizations.js

@@ -223,7 +223,7 @@ function optPassMergeVarInitializationAssignments(ast) {
 }
 
 function runOnJsText(js, pretty = false) {
-  const ast = acorn.parse(js, {ecmaVersion: 2020});
+  const ast = acorn.parse(js, {ecmaVersion: 2021});
 
   optPassSimplifyModuleInitialization(ast);
   optPassRemoveRedundantOperatorNews(ast);