[fix] cross-browser flex styles

Fix #616
Close #648

src/apis/AppRegistry/__tests__/__snapshots__/renderApplication-test.js.snap

@@ -50,10 +50,9 @@ exports[`apis/AppRegistry/renderApplication getApplication 3`] = `
 .rn-boxSizing-deolkf{box-sizing:border-box}
 .rn-display-6koalj{display:-webkit-box;display:-moz-box;display:-ms-flexbox;display:-webkit-flex;display:flex}
 .rn-display-xoduu5{display:-webkit-inline-box;display:-moz-inline-box;display:-ms-inline-flexbox;display:-webkit-inline-flex;display:inline-flex}
-.rn-flexShrink-1qe8dj5{-webkit-flex-shrink:0;flex-shrink:0}
-.rn-flexShrink-1wbh5a2{-webkit-flex-shrink:1;flex-shrink:1}
-.rn-flexBasis-1mlwlqe{-webkit-flex-basis:auto;flex-basis:auto}
-.rn-flexBasis-1ro0kt6{-webkit-flex-basis:0%;flex-basis:0%}
+.rn-flexShrink-1pxmb3b{-webkit-flex-shrink:0 !important;flex-shrink:0 !important}
+.rn-flexShrink-1awmn5t{-webkit-flex-shrink:1 !important;flex-shrink:1 !important}
+.rn-flexBasis-7vfszb{-webkit-flex-basis:auto !important;flex-basis:auto !important}
 .rn-flexDirection-eqz5dr{-webkit-box-direction:normal;-webkit-box-orient:vertical;-webkit-flex-direction:column;flex-direction:column}
 .rn-marginTop-1mnahxq{margin-top:0px}
 .rn-marginRight-61z16t{margin-right:0px}
@@ -67,5 +66,6 @@ exports[`apis/AppRegistry/renderApplication getApplication 3`] = `
 .rn-paddingLeft-gy4na3{padding-left:0px}
 .rn-zIndex-1lgpqti{z-index:0}
 .rn-zIndex-1wyyakw{z-index:-1}
-.rn-flexGrow-16y2uox{-webkit-flex-grow:1;flex-grow:1}</style>"
+.rn-flex-13awgt0{-webkit-flex:1;flex:1}
+.rn-flexGrow-1m1wadx{-webkit-flex-grow:1 !important;flex-grow:1 !important}</style>"
 `;

src/apis/StyleSheet/__tests__/createReactDOMStyle-test.js

@@ -26,44 +26,44 @@ describe('apis/StyleSheet/createReactDOMStyle', () => {
     test('flex defaults', () => {
       expect(createReactDOMStyle({ display: 'flex' })).toEqual({
         display: 'flex',
-        flexShrink: 0,
-        flexBasis: 'auto'
+        flexShrink: '0 !important',
+        flexBasis: 'auto !important'
       });
     });
 
     test('flex: -1', () => {
       expect(createReactDOMStyle({ display: 'flex', flex: -1 })).toEqual({
         display: 'flex',
-        flexGrow: 0,
-        flexShrink: 1,
-        flexBasis: 'auto'
+        flexGrow: '0 !important',
+        flexShrink: '1 !important',
+        flexBasis: 'auto !important'
       });
     });
 
     test('flex: 0', () => {
       expect(createReactDOMStyle({ display: 'flex', flex: 0 })).toEqual({
         display: 'flex',
-        flexGrow: 0,
-        flexShrink: 0,
-        flexBasis: 'auto'
+        flexGrow: '0 !important',
+        flexShrink: '0 !important',
+        flexBasis: 'auto !important'
       });
     });
 
     test('flex: 1', () => {
       expect(createReactDOMStyle({ display: 'flex', flex: 1 })).toEqual({
         display: 'flex',
-        flexGrow: 1,
-        flexShrink: 1,
-        flexBasis: '0%'
+        flex: 1,
+        flexGrow: '1 !important',
+        flexShrink: '1 !important'
       });
     });
 
     test('flex: 10', () => {
       expect(createReactDOMStyle({ display: 'flex', flex: 10 })).toEqual({
         display: 'flex',
-        flexGrow: 10,
-        flexShrink: 1,
-        flexBasis: '0%'
+        flex: 10,
+        flexGrow: '10 !important',
+        flexShrink: '1 !important'
       });
     });
 
@@ -71,16 +71,17 @@ describe('apis/StyleSheet/createReactDOMStyle', () => {
       // is flex-basis applied?
       expect(createReactDOMStyle({ display: 'flex', flexBasis: '25%' })).toEqual({
         display: 'flex',
-        flexShrink: 0,
-        flexBasis: '25%'
+        flexShrink: '0 !important',
+        flexBasis: '25% !important'
       });
 
       // can flex-basis override the 'flex' expansion?
       expect(createReactDOMStyle({ display: 'flex', flex: 1, flexBasis: '25%' })).toEqual({
         display: 'flex',
-        flexGrow: 1,
-        flexShrink: 1,
-        flexBasis: '25%'
+        flex: 1,
+        flexGrow: '1 !important',
+        flexShrink: '1 !important',
+        flexBasis: '25% !important'
       });
     });
 
@@ -88,16 +89,16 @@ describe('apis/StyleSheet/createReactDOMStyle', () => {
       // is flex-shrink applied?
       expect(createReactDOMStyle({ display: 'flex', flexShrink: 1 })).toEqual({
         display: 'flex',
-        flexShrink: 1,
-        flexBasis: 'auto'
+        flexShrink: '1 !important',
+        flexBasis: 'auto !important'
       });
 
       // can flex-shrink override the 'flex' expansion?
       expect(createReactDOMStyle({ display: 'flex', flex: 1, flexShrink: 2 })).toEqual({
         display: 'flex',
-        flexGrow: 1,
-        flexShrink: 2,
-        flexBasis: '0%'
+        flex: 1,
+        flexGrow: '1 !important',
+        flexShrink: '2 !important'
       });
     });
   });

src/apis/StyleSheet/createReactDOMStyle.js

@@ -158,29 +158,56 @@ const createReducer = (style, styleProps) => {
 
       case 'display': {
         resolvedStyle.display = value;
-        // defaults of 'flexBasis:auto' and 'flexShrink:0' have lowest precedence
-        if (style.display === 'flex') {
+        // A flex container in React Native has these defaults which should be
+        // set only if there is no otherwise supplied flex style.
+        if (style.display === 'flex' && style.flex == null) {
           if (style.flexShrink == null) {
-            resolvedStyle.flexShrink = 0;
+            resolvedStyle.flexShrink = '0 !important';
           }
           if (style.flexBasis == null) {
-            resolvedStyle.flexBasis = 'auto';
+            resolvedStyle.flexBasis = 'auto !important';
           }
         }
         break;
       }
 
+      // The 'flex' property value in React Native must be a positive integer,
+      // 0, or -1.
+      //
+      // On the web, a positive integer value for 'flex' is complicated by
+      // browser differences. Although browsers render styles like 'flex:2'
+      // consistently, they don't all set the same value for the resulting
+      // 'flexBasis' (See #616). Expanding 'flex' in 'StyleSheet' would mean
+      // setting different values for different browsers.
+      //
+      // This fix instead relies on the browser expanding 'flex' itself. And
+      // because the 'flex' style is not being expanded the generated CSS is
+      // likely to contain source order "conflicts". To avoid the browser
+      // relying on source order to resolve the styles, all the longhand flex
+      // property values must use '!important'.
       case 'flex': {
         if (value > 0) {
-          resolvedStyle.flexGrow = value;
-          resolvedStyle.flexShrink = 1;
-          resolvedStyle.flexBasis = '0%';
+          resolvedStyle.flex = value;
+          resolvedStyle.flexGrow = `${value} !important`;
+          resolvedStyle.flexShrink = '1 !important';
         } else if (value === 0) {
-          resolvedStyle.flexGrow = 0;
-          resolvedStyle.flexShrink = 0;
+          resolvedStyle.flexGrow = '0 !important';
+          resolvedStyle.flexShrink = '0 !important';
+          resolvedStyle.flexBasis = 'auto !important';
         } else if (value === -1) {
-          resolvedStyle.flexGrow = 0;
-          resolvedStyle.flexShrink = 1;
+          resolvedStyle.flexGrow = '0 !important';
+          resolvedStyle.flexShrink = '1 !important';
+          resolvedStyle.flexBasis = 'auto !important';
+        }
+        break;
+      }
+
+      case 'flexGrow':
+      case 'flexShrink':
+      case 'flexBasis': {
+        if (value != null) {
+          const hasImportant = `${value}`.indexOf('!important') > -1;
+          resolvedStyle[prop] = hasImportant ? value : `${value} !important`;
         }
         break;
       }