Immediately destructure out propVariables rather than using it as a namespace

Author: chiawendt

lib/util/usedPropTypes.js

@@ -39,7 +39,7 @@ function createPropVariables() {
       if (!hasBeenWritten) {
         // copy on write
         propVariables = new Map(propVariables);
-        Object.assign(stack[stack.length - 1], { propVariables, hasBeenWritten: true });
+        Object.assign(stack[stack.length - 1], {propVariables, hasBeenWritten: true});
         stack[stack.length - 1].hasBeenWritten = true;
       }
       return propVariables.set(name, allNames);
@@ -271,6 +271,8 @@ module.exports = function usedPropTypesInstructions(context, components, utils)
   const checkAsyncSafeLifeCycles = versionUtil.testReactVersion(context, '16.3.0');
 
   const propVariables = createPropVariables();
+  const pushScope = propVariables.pushScope;
+  const popScope = propVariables.popScope;
 
   /**
    * Mark a prop type as used
@@ -422,7 +424,7 @@ module.exports = function usedPropTypesInstructions(context, components, utils)
    *   FunctionDeclaration, or FunctionExpression
    */
   function handleFunctionLikeExpressions(node) {
-    propVariables.pushScope();
+    pushScope();
     handleSetStateUpdater(node);
     markDestructuredFunctionArgumentsAsUsed(node);
   }
@@ -497,11 +499,11 @@ module.exports = function usedPropTypesInstructions(context, components, utils)
 
     FunctionExpression: handleFunctionLikeExpressions,
 
-    'FunctionDeclaration:exit': propVariables.popScope,
+    'FunctionDeclaration:exit': popScope,
 
-    'ArrowFunctionExpression:exit': propVariables.popScope,
+    'ArrowFunctionExpression:exit': popScope,
 
-    'FunctionExpression:exit': propVariables.popScope,
+    'FunctionExpression:exit': popScope,
 
     JSXSpreadAttribute(node) {
       const component = components.get(utils.getParentComponent());