Do not modify AST directly (fixes #249)

Author: rhysd

lib/rules/forbid-prop-types.js

@@ -54,24 +54,25 @@ module.exports = function(context) {
   function checkForbidden(declarations) {
     declarations.forEach(function(declaration) {
       var target;
+      var value = declaration.value;
       if (
-        declaration.value.type === 'MemberExpression' &&
-        declaration.value.property &&
-        declaration.value.property.name &&
-        declaration.value.property.name === 'isRequired'
+        value.type === 'MemberExpression' &&
+        value.property &&
+        value.property.name &&
+        value.property.name === 'isRequired'
       ) {
-        declaration.value = declaration.value.object;
+        value = value.object;
       }
       if (
-        declaration.value.type === 'CallExpression' &&
-        declaration.value.callee.type === 'MemberExpression'
+        value.type === 'CallExpression' &&
+        value.callee.type === 'MemberExpression'
       ) {
-        declaration.value = declaration.value.callee;
+        value = value.callee;
       }
-      if (declaration.value.property) {
-        target = declaration.value.property.name;
-      } else if (declaration.value.type === 'Identifier') {
-        target = declaration.value.name;
+      if (value.property) {
+        target = value.property.name;
+      } else if (value.type === 'Identifier') {
+        target = value.name;
       }
       if (isForbidden(target)) {
         context.report(declaration, 'Prop type `' + target + '` is forbidden');