Es6RewriteGenerators: correct use of ExpressionDecomposer

ExpressionDecomposer#maybeExposeExpression() guarantees the expression
is fully exposed and should be used instead of exposeExpression().

PiperOrigin-RevId: 321817366

Author: brad4d

src/com/google/javascript/jscomp/Es6RewriteGenerators.java

@@ -191,7 +191,7 @@ void visitYield(Node n) {
       }
       if (decomposer.canExposeExpression(n)
           != ExpressionDecomposer.DecompositionType.UNDECOMPOSABLE) {
-        decomposer.exposeExpression(n);
+        decomposer.maybeExposeExpression(n);
       } else {
         String link =
             "https://github.com/google/closure-compiler/wiki/FAQ"

test/com/google/javascript/jscomp/Es6RewriteGeneratorsTest.java

@@ -463,32 +463,35 @@ public void testDecomposeComplexYieldExpression() {
             "}"),
         lines(
             "function f(){",
-            "var obj;",
-            "var JSCompiler_temp$jscomp$0;",
-            "var JSCompiler_temp_const$jscomp$2;",
-            "var JSCompiler_temp_const$jscomp$1;",
-            "return $jscomp.generator.createGenerator(f,function($jscomp$generator$context) {",
-            "  switch($jscomp$generator$context.nextAddress) {",
-            "    case 1:",
-            "      obj = {bar:function(x){}};",
-            "      return $jscomp$generator$context.yield(5,2);",
-            "    case 2:",
-            "      if (!(JSCompiler_temp$jscomp$0 = $jscomp$generator$context.yieldResult)) {",
-            "        $jscomp$generator$context.jumpTo(3);",
-            "        break;",
-            "      }",
-            "      JSCompiler_temp_const$jscomp$2 = obj;",
-            "      JSCompiler_temp_const$jscomp$1 = JSCompiler_temp_const$jscomp$2.bar;",
-            "      return $jscomp$generator$context.yield(5,4);",
-            "    case 4:",
-            "      JSCompiler_temp$jscomp$0 = JSCompiler_temp_const$jscomp$1.call(",
-            "          JSCompiler_temp_const$jscomp$2,",
-            "          $jscomp$generator$context.yieldResult);",
-            "    case 3:",
-            "      JSCompiler_temp$jscomp$0;",
-            "      $jscomp$generator$context.jumpToEnd();",
-            "   }",
-            " })",
+            "  var obj;",
+            "  var JSCompiler_temp$jscomp$0;",
+            "  var JSCompiler_temp_const$jscomp$2;",
+            "  var JSCompiler_temp_const$jscomp$1;",
+            "  var JSCompiler_temp_const$jscomp$3;",
+            "  return $jscomp.generator.createGenerator(f, function($jscomp$generator$context) {",
+            "    switch($jscomp$generator$context.nextAddress) {",
+            "      case 1:",
+            "        obj = {bar:function(x) {}};",
+            "        return $jscomp$generator$context.yield(5, 2);",
+            "      case 2:",
+            "        if (!(JSCompiler_temp$jscomp$0 = $jscomp$generator$context.yieldResult)) {",
+            "          $jscomp$generator$context.jumpTo(3);",
+            "          break;",
+            "        }",
+            "        JSCompiler_temp_const$jscomp$2 = obj;",
+            "        JSCompiler_temp_const$jscomp$1 = JSCompiler_temp_const$jscomp$2.bar;",
+            "        JSCompiler_temp_const$jscomp$3 = JSCompiler_temp_const$jscomp$2;",
+            "        return $jscomp$generator$context.yield(5, 4);",
+            "      case 4:",
+            "        JSCompiler_temp$jscomp$0 =", 
+            "            JSCompiler_temp_const$jscomp$1.call(",
+            "                JSCompiler_temp_const$jscomp$3,",
+            "                $jscomp$generator$context.yieldResult);",
+            "      case 3:",
+            "        JSCompiler_temp$jscomp$0;",
+            "        $jscomp$generator$context.jumpToEnd();",
+            "    }",
+            "  });",
             "}"));
   }