Fix 2377: Throw error when trying to stub non-configurable or non-writable properties (#2417)

Fixes issue #2377 by throwing an error when trying to stub non-configurable or non-writable properties

Author: sdotson

lib/sinon/stub.js

@@ -81,6 +81,9 @@ function stub(object, property) {
     }
 
     var actualDescriptor = getPropertyDescriptor(object, property);
+
+    assertValidPropertyDescriptor(actualDescriptor, property);
+
     var isObjectOrFunction =
         typeof object === "object" || typeof object === "function";
     var isStubbingEntireObject =
@@ -147,6 +150,25 @@ stub.createStubInstance = function (constructor, overrides) {
     return stubbedObject;
 };
 
+function assertValidPropertyDescriptor(descriptor, property) {
+    if (!descriptor ||  !property) {
+        return;
+    }
+    if (!descriptor.configurable && !descriptor.writable) {
+        throw new TypeError(`Descriptor for property ${property} is non-configurable and non-writable`);
+    }
+    if ((descriptor.get || descriptor.set) && !descriptor.configurable) {
+        throw new TypeError(`Descriptor for accessor property ${property} is non-configurable`);
+    }
+    if (isDataDescriptor(descriptor) && !descriptor.writable) {
+        throw new TypeError(`Descriptor for data property ${property} is non-writable`);
+    }
+}
+
+function isDataDescriptor(descriptor) {
+    return !descriptor.value && !descriptor.writable && !descriptor.set && !descriptor.get;
+}
+
 /*eslint-disable no-use-before-define*/
 function getParentBehaviour(stubInstance) {
     return stubInstance.parent && getCurrentBehavior(stubInstance.parent);

test/shared-spy-stub-everything-tests.js

@@ -151,4 +151,51 @@ module.exports = function shared(createSpyOrStub) {
 
         assert.isUndefined(myObj.ouch);
     });
+
+    it("throws on data property descriptors that are not writable or configurable", function () {
+        var myObj = {};
+        Object.defineProperty(myObj, 'ignoreme', {
+            writable: false,
+            configurable: false
+        });
+
+        assert.exception(function () {
+                createSpyOrStub(myObj, "ignoreme");
+            }, 
+            new TypeError('Descriptor for property ignoreme is non-configurable and non-writable')
+        );
+    });
+
+    it("throws on accessor property descriptors that are not configurable", function () {
+        var myObj = {};
+        Object.defineProperty(myObj, 'ignoreme', {
+            get: function(key) {
+                return this[key];
+            },
+            set: function(key, val) {
+                this[key] = val;
+            },
+            configurable: false
+        });
+
+        assert.exception(function () {
+                createSpyOrStub(myObj, "ignoreme");
+            },
+            new TypeError('Descriptor for accessor property ignoreme is non-configurable')
+        );
+    });
+
+    it("throws on data descriptors that are not stubbable", function () {
+        var myObj = {};
+        Object.defineProperty(myObj, 'ignoreme', {
+            writable: false,
+            configurable: false
+        });
+
+        assert.exception(function () {
+                createSpyOrStub(myObj, "ignoreme");
+            }, 
+            new TypeError('Descriptor for data property ignoreme is non-writable')
+        );
+    });
 };