WIP Downgrade deprecation warnings from errors to warnings

**RFC:**
Pushing this for feedback while I fix all the failing tests.

**what is the change?:**
Swapping out `warning` module for a fork that uses `console.warn`.
It looks like we were using the `warning` module for deprecation notices, *but* there is also a 'deprecated' module designed specifically for deprecation notices.

However, we could not find any place that it was currently used.

Since React's build process is not 100% clear to me, I assume it could still be used somewhere by something and just updated it along with other deprecation notices.

We might consider a follow-up diff that does some clean up here;
 - remove 'deprecated' module if it's unused, OR
 - use 'deprecated' module for all our current deprecation warnings

**why make this change?:**
- We have had complaints about noisy warnings, in particular after introducing new deprecations
- They potentially cause CI failures
- Deprecations are not really time-sensitive, can ship without breaking your app, etc.

For more context - facebook#9395

**test plan:**
`npm run test`
and unit tests for the new modules
and manual testing (WIP)

**issue:**
facebook#9395

src/addons/__tests__/ReactDOMFactories-test.js

@@ -17,22 +17,24 @@ var {div} = require('ReactDOMFactories');
 describe('ReactDOMFactories', () => {
   it('allow factories to be called without warnings', () => {
     spyOn(console, 'error');
+    spyOn(console, 'warn');
     var element = div();
     expect(element.type).toBe('div');
     expect(console.error).not.toHaveBeenCalled();
+    expect(console.warn).not.toHaveBeenCalled();
   });
 
   it('warns once when accessing React.DOM methods', () => {
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
 
     var a = React.DOM.a();
     var p = React.DOM.p();
 
     expect(a.type).toBe('a');
     expect(p.type).toBe('p');
 
-    expect(console.error).toHaveBeenCalledTimes(1);
-    expect(console.error.calls.first().args[0]).toContain(
+    expect(console.warn).toHaveBeenCalledTimes(1);
+    expect(console.warn.calls.first().args[0]).toContain(
       'Warning: Accessing factories like React.DOM.a has been deprecated',
     );
   });

src/isomorphic/React.js

@@ -27,7 +27,7 @@ var createFactory = ReactElement.createFactory;
 var cloneElement = ReactElement.cloneElement;
 
 if (__DEV__) {
-  var warning = require('fbjs/lib/warning');
+  var lowPriorityWarning = require('lowPriorityWarning');
   var canDefineProperty = require('canDefineProperty');
   var ReactElementValidator = require('ReactElementValidator');
   createElement = ReactElementValidator.createElement;
@@ -91,7 +91,7 @@ if (__DEV__) {
   let warnedForPropTypes = false;
 
   React.createMixin = function(mixin) {
-    warning(
+    lowPriorityWarning(
       warnedForCreateMixin,
       'React.createMixin is deprecated and should not be used. You ' +
         'can use this mixin directly instead.',
@@ -104,7 +104,7 @@ if (__DEV__) {
   if (canDefineProperty) {
     Object.defineProperty(React, 'checkPropTypes', {
       get() {
-        warning(
+        lowPriorityWarning(
           warnedForCheckPropTypes,
           'checkPropTypes has been moved to a separate package. ' +
             'Accessing React.checkPropTypes is no longer supported ' +
@@ -119,7 +119,7 @@ if (__DEV__) {
 
     Object.defineProperty(React, 'createClass', {
       get: function() {
-        warning(
+        lowPriorityWarning(
           warnedForCreateClass,
           'React.createClass is no longer supported. Use a plain JavaScript ' +
             "class instead. If you're not yet ready to migrate, " +
@@ -133,7 +133,7 @@ if (__DEV__) {
 
     Object.defineProperty(React, 'PropTypes', {
       get() {
-        warning(
+        lowPriorityWarning(
           warnedForPropTypes,
           'PropTypes has been moved to a separate package. ' +
             'Accessing React.PropTypes is no longer supported ' +
@@ -155,7 +155,7 @@ if (__DEV__) {
   Object.keys(ReactDOMFactories).forEach(function(factory) {
     React.DOM[factory] = function(...args) {
       if (!warnedForFactories) {
-        warning(
+        lowPriorityWarning(
           false,
           'Accessing factories like React.DOM.%s has been deprecated ' +
             'and will be removed in the future. Use the ' +

src/isomorphic/__tests__/React-test.js

@@ -19,22 +19,22 @@ describe('React', () => {
   });
 
   it('should log a deprecation warning once when using React.createMixin', () => {
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
     React.createMixin();
     React.createMixin();
-    expectDev(console.error.calls.count()).toBe(1);
-    expectDev(console.error.calls.argsFor(0)[0]).toContain(
+    expectDev(console.warn.calls.count()).toBe(1);
+    expectDev(console.warn.calls.argsFor(0)[0]).toContain(
       'React.createMixin is deprecated and should not be used',
     );
   });
 
   it('should warn once when attempting to access React.createClass', () => {
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
     let createClass = React.createClass;
     createClass = React.createClass;
     expect(createClass).not.toBe(undefined);
-    expectDev(console.error.calls.count()).toBe(1);
-    expectDev(console.error.calls.argsFor(0)[0]).toContain(
+    expectDev(console.warn.calls.count()).toBe(1);
+    expectDev(console.warn.calls.argsFor(0)[0]).toContain(
       'React.createClass is no longer supported. Use a plain JavaScript ' +
         "class instead. If you're not yet ready to migrate, " +
         'create-react-class is available on npm as a drop-in replacement. ' +
@@ -43,12 +43,12 @@ describe('React', () => {
   });
 
   it('should warn once when attempting to access React.PropTypes', () => {
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
     let PropTypes = React.PropTypes;
     PropTypes = React.PropTypes;
     expect(PropTypes).not.toBe(undefined);
-    expectDev(console.error.calls.count()).toBe(1);
-    expectDev(console.error.calls.argsFor(0)[0]).toContain(
+    expectDev(console.warn.calls.count()).toBe(1);
+    expectDev(console.warn.calls.argsFor(0)[0]).toContain(
       'PropTypes has been moved to a separate package. ' +
         'Accessing React.PropTypes is no longer supported ' +
         'and will be removed completely in React 16. ' +
@@ -58,12 +58,12 @@ describe('React', () => {
   });
 
   it('should warn once when attempting to access React.checkPropTypes', () => {
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
     let checkPropTypes = React.checkPropTypes;
     checkPropTypes = React.checkPropTypes;
     expect(checkPropTypes).not.toBe(undefined);
-    expectDev(console.error.calls.count()).toBe(1);
-    expectDev(console.error.calls.argsFor(0)[0]).toContain(
+    expectDev(console.warn.calls.count()).toBe(1);
+    expectDev(console.warn.calls.argsFor(0)[0]).toContain(
       'checkPropTypes has been moved to a separate package. ' +
         'Accessing React.checkPropTypes is no longer supported ' +
         'and will be removed completely in React 16. ' +

src/isomorphic/classic/element/ReactElementValidator.js

@@ -27,8 +27,9 @@ var getIteratorFn = require('getIteratorFn');
 
 if (__DEV__) {
   var checkPropTypes = require('prop-types/checkPropTypes');
-  var warning = require('fbjs/lib/warning');
+  var lowPriorityWarning = require('lowPriorityWarning');
   var ReactDebugCurrentFrame = require('ReactDebugCurrentFrame');
+  var warning = require('fbjs/lib/warning');
   var {getCurrentStackAddendum} = require('ReactComponentTreeHook');
 }
 
@@ -285,7 +286,7 @@ var ReactElementValidator = {
         Object.defineProperty(validatedFactory, 'type', {
           enumerable: false,
           get: function() {
-            warning(
+            lowPriorityWarning(
               false,
               'Factory.type is deprecated. Access the class directly ' +
                 'before passing it to createFactory.',

src/isomorphic/classic/element/__tests__/ReactElementValidator-test.js

@@ -441,20 +441,20 @@ describe('ReactElementValidator', () => {
   });
 
   it('should warn when accessing .type on an element factory', () => {
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
     function TestComponent() {
       return <div />;
     }
     var TestFactory = React.createFactory(TestComponent);
     expect(TestFactory.type).toBe(TestComponent);
-    expectDev(console.error.calls.count()).toBe(1);
-    expectDev(console.error.calls.argsFor(0)[0]).toBe(
+    expectDev(console.warn.calls.count()).toBe(1);
+    expectDev(console.warn.calls.argsFor(0)[0]).toBe(
       'Warning: Factory.type is deprecated. Access the class directly before ' +
         'passing it to createFactory.',
     );
     // Warn once, not again
     expect(TestFactory.type).toBe(TestComponent);
-    expectDev(console.error.calls.count()).toBe(1);
+    expectDev(console.warn.calls.count()).toBe(1);
   });
 
   it('does not warn when using DOM node as children', () => {

src/isomorphic/modern/class/ReactBaseClasses.js

@@ -16,7 +16,7 @@ var ReactNoopUpdateQueue = require('ReactNoopUpdateQueue');
 var canDefineProperty = require('canDefineProperty');
 var emptyObject = require('fbjs/lib/emptyObject');
 var invariant = require('fbjs/lib/invariant');
-var warning = require('fbjs/lib/warning');
+var lowPriorityWarning = require('lowPriorityWarning');
 
 /**
  * Base class helpers for the updating state of a component.
@@ -108,7 +108,7 @@ if (__DEV__) {
     if (canDefineProperty) {
       Object.defineProperty(ReactComponent.prototype, methodName, {
         get: function() {
-          warning(
+          lowPriorityWarning(
             false,
             '%s(...) is deprecated in plain JavaScript React classes. %s',
             info[0],

src/isomorphic/modern/class/__tests__/ReactCoffeeScriptClass-test.coffee

@@ -378,16 +378,16 @@ describe 'ReactCoffeeScriptClass', ->
     undefined
 
   it 'should throw AND warn when trying to access classic APIs', ->
-    spyOn console, 'error'
+    spyOn console, 'warn'
     instance =
       test Inner(name: 'foo'), 'DIV', 'foo'
     expect(-> instance.replaceState {}).toThrow()
     expect(-> instance.isMounted()).toThrow()
-    expect(console.error.calls.count()).toBe 2
-    expect(console.error.calls.argsFor(0)[0]).toContain(
+    expect(console.warn.calls.count()).toBe 2
+    expect(console.warn.calls.argsFor(0)[0]).toContain(
       'replaceState(...) is deprecated in plain JavaScript React classes'
     )
-    expect(console.error.calls.argsFor(1)[0]).toContain(
+    expect(console.warn.calls.argsFor(1)[0]).toContain(
       'isMounted(...) is deprecated in plain JavaScript React classes'
     )
     undefined

src/isomorphic/modern/class/__tests__/ReactES6Class-test.js

@@ -402,15 +402,15 @@ describe('ReactES6Class', () => {
   });
 
   it('should throw AND warn when trying to access classic APIs', () => {
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
     var instance = test(<Inner name="foo" />, 'DIV', 'foo');
     expect(() => instance.replaceState({})).toThrow();
     expect(() => instance.isMounted()).toThrow();
-    expect(console.error.calls.count()).toBe(2);
-    expect(console.error.calls.argsFor(0)[0]).toContain(
+    expect(console.warn.calls.count()).toBe(2);
+    expect(console.warn.calls.argsFor(0)[0]).toContain(
       'replaceState(...) is deprecated in plain JavaScript React classes',
     );
-    expect(console.error.calls.argsFor(1)[0]).toContain(
+    expect(console.warn.calls.argsFor(1)[0]).toContain(
       'isMounted(...) is deprecated in plain JavaScript React classes',
     );
   });

src/isomorphic/modern/class/__tests__/ReactTypeScriptClass-test.ts

@@ -502,18 +502,18 @@ describe('ReactTypeScriptClass', function() {
   });
 
   it('should throw AND warn when trying to access classic APIs', function() {
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
     var instance = test(
       React.createElement(Inner, {name: 'foo'}),
       'DIV','foo'
     );
     expect(() => instance.replaceState({})).toThrow();
     expect(() => instance.isMounted()).toThrow();
-    expect((<any>console.error).calls.count()).toBe(2);
-    expect((<any>console.error).calls.argsFor(0)[0]).toContain(
+    expect((<any>console.warn).calls.count()).toBe(2);
+    expect((<any>console.warn).calls.argsFor(0)[0]).toContain(
       'replaceState(...) is deprecated in plain JavaScript React classes'
     );
-    expect((<any>console.error).calls.argsFor(1)[0]).toContain(
+    expect((<any>console.warn).calls.argsFor(1)[0]).toContain(
       'isMounted(...) is deprecated in plain JavaScript React classes'
     );
   });

src/renderers/__tests__/ReactCompositeComponentState-test.js

@@ -406,7 +406,7 @@ describe('ReactCompositeComponent-state', () => {
   });
 
   it('should treat assigning to this.state inside cWRP as a replaceState, with a warning', () => {
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
 
     let ops = [];
     class Test extends React.Component {
@@ -440,8 +440,8 @@ describe('ReactCompositeComponent-state', () => {
       'render -- step: 3, extra: false',
       'callback -- step: 3, extra: false',
     ]);
-    expect(console.error.calls.count()).toEqual(1);
-    expect(console.error.calls.argsFor(0)[0]).toEqual(
+    expect(console.warn.calls.count()).toEqual(1);
+    expect(console.warn.calls.argsFor(0)[0]).toEqual(
       'Warning: Test.componentWillReceiveProps(): Assigning directly to ' +
         "this.state is deprecated (except inside a component's constructor). " +
         'Use setState instead.',

src/renderers/__tests__/ReactPerf-test.js

@@ -406,30 +406,30 @@ describeStack('ReactPerf', () => {
 
   it('warns once when using getMeasurementsSummaryMap', () => {
     var measurements = measure(() => {});
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
     ReactPerf.getMeasurementsSummaryMap(measurements);
-    expectDev(console.error.calls.count()).toBe(1);
-    expectDev(console.error.calls.argsFor(0)[0]).toContain(
+    expectDev(console.warn.calls.count()).toBe(1);
+    expectDev(console.warn.calls.argsFor(0)[0]).toContain(
       '`ReactPerf.getMeasurementsSummaryMap(...)` is deprecated. Use ' +
         '`ReactPerf.getWasted(...)` instead.',
     );
 
     ReactPerf.getMeasurementsSummaryMap(measurements);
-    expectDev(console.error.calls.count()).toBe(1);
+    expectDev(console.warn.calls.count()).toBe(1);
   });
 
-  it('warns once when using printDOM', () => {
+  fit('warns once when using printDOM', () => {
     var measurements = measure(() => {});
-    spyOn(console, 'error');
+    spyOn(console, 'warn');
     ReactPerf.printDOM(measurements);
-    expectDev(console.error.calls.count()).toBe(1);
-    expectDev(console.error.calls.argsFor(0)[0]).toContain(
+    expectDev(console.warn.calls.count()).toBe(1);
+    expectDev(console.warn.calls.argsFor(0)[0]).toContain(
       '`ReactPerf.printDOM(...)` is deprecated. Use ' +
         '`ReactPerf.printOperations(...)` instead.',
     );
 
     ReactPerf.printDOM(measurements);
-    expectDev(console.error.calls.count()).toBe(1);
+    expectDev(console.warn.calls.count()).toBe(1);
   });
 
   it('returns isRunning state', () => {

src/renderers/native/__tests__/__snapshots__/ReactNativeEvents-test.js.snap

@@ -1,7 +1,11 @@
-// Jest Snapshot v1, https://goo.gl/fbAQLP
-
 exports[`handles events 1`] = `
 "<native root> {}
-  View {\\"foo\\":\\"outer\\"}
-    View {\\"foo\\":\\"inner\\"}"
+  View {"foo":"outer"}
+    View {"foo":"inner"}"
+`;
+
+exports[`test handles events 1`] = `
+"<native root> {}
+  View {\"foo\":\"outer\"}
+    View {\"foo\":\"inner\"}"
 `;

src/renderers/shared/ReactPerf.js

@@ -13,7 +13,7 @@
 'use strict';
 
 var ReactDebugTool = require('ReactDebugTool');
-var warning = require('fbjs/lib/warning');
+var lowPriorityWarning = require('lowPriorityWarning');
 var alreadyWarned = false;
 
 import type {FlushHistory} from 'ReactDebugTool';
@@ -390,7 +390,7 @@ function printOperations(flushHistory?: FlushHistory) {
 
 var warnedAboutPrintDOM = false;
 function printDOM(measurements: FlushHistory) {
-  warning(
+  lowPriorityWarning(
     warnedAboutPrintDOM,
     '`ReactPerf.printDOM(...)` is deprecated. Use ' +
       '`ReactPerf.printOperations(...)` instead.',
@@ -401,7 +401,7 @@ function printDOM(measurements: FlushHistory) {
 
 var warnedAboutGetMeasurementsSummaryMap = false;
 function getMeasurementsSummaryMap(measurements: FlushHistory) {
-  warning(
+  lowPriorityWarning(
     warnedAboutGetMeasurementsSummaryMap,
     '`ReactPerf.getMeasurementsSummaryMap(...)` is deprecated. Use ' +
       '`ReactPerf.getWasted(...)` instead.',

src/renderers/shared/fiber/ReactFiberClassComponent.js

@@ -45,6 +45,7 @@ const isArray = Array.isArray;
 if (__DEV__) {
   var {startPhaseTimer, stopPhaseTimer} = require('ReactDebugFiberPerf');
   var warning = require('fbjs/lib/warning');
+  var lowPriorityWarning = require('lowPriorityWarning');
   var warnOnInvalidCallback = function(callback: mixed, callerName: string) {
     warning(
       callback === null || typeof callback === 'function',
@@ -316,7 +317,7 @@ module.exports = function(
 
     if (oldState !== instance.state) {
       if (__DEV__) {
-        warning(
+        lowPriorityWarning(
           false,
           '%s.componentWillMount(): Assigning directly to this.state is ' +
             "deprecated (except inside a component's " +
@@ -345,7 +346,7 @@ module.exports = function(
 
     if (instance.state !== oldState) {
       if (__DEV__) {
-        warning(
+        lowPriorityWarning(
           false,
           '%s.componentWillReceiveProps(): Assigning directly to ' +
             "this.state is deprecated (except inside a component's " +