Make IE 11 not complain about non-crucial style attribute hydration mismatch

IE 11 parses & normalizes the style attribute as opposed to other
browsers. It adds spaces and sorts the properties in some
non-alphabetical order. Handling that would require sorting CSS
properties in the client & server versions or applying
`expectedStyle` to a temporary DOM node to read its `style` attribute
normalized. Since it only affects IE, we're skipping style warnings
in that browser completely in favor of doing all that work.

Fixes #11807

Author: mgol

packages/react-dom/src/__tests__/ReactServerRenderingHydration.js

@@ -258,6 +258,67 @@ describe('ReactDOMServerHydration', () => {
     expect(element.firstChild.focus).not.toHaveBeenCalled();
   });
 
+  it('should warn when the style property differs', () => {
+    const element = document.createElement('div');
+    element.innerHTML = ReactDOMServer.renderToString(
+      <div style={{textDecoration: 'none', color: 'black', height: '10px'}} />,
+    );
+    expect(element.firstChild.style.textDecoration).toBe('none');
+    expect(element.firstChild.style.color).toBe('black');
+
+    expect(() =>
+      ReactDOM.hydrate(
+        <div
+          style={{textDecoration: 'none', color: 'white', height: '10px'}}
+        />,
+        element,
+      ),
+    ).toWarnDev(
+      'Warning: Prop `style` did not match. Server: ' +
+        '"text-decoration:none;color:black;height:10px" Client: ' +
+        '"text-decoration:none;color:white;height:10px"',
+      {withoutStack: true},
+    );
+  });
+
+  it('should not warn when the style property differs on whitespace or order in IE', () => {
+    document.documentMode = 11;
+    const element = document.createElement('div');
+
+    // Simulate IE normalizing the style attribute. IE makes it equal to
+    // what's available under `node.style.cssText`.
+    element.innerHTML =
+      '<div style="height: 10px; color: black; text-decoration: none;" data-reactroot=""></div>';
+
+    ReactDOM.hydrate(
+      <div style={{textDecoration: 'none', color: 'black', height: '10px'}} />,
+      element,
+    );
+
+    delete document.documentMode;
+  });
+
+  it('should warn when the style property differs on whitespace in non-IE browsers', () => {
+    const element = document.createElement('div');
+
+    element.innerHTML =
+      '<div style="text-decoration: none; color: black; height: 10px;" data-reactroot=""></div>';
+
+    expect(() =>
+      ReactDOM.hydrate(
+        <div
+          style={{textDecoration: 'none', color: 'black', height: '10px'}}
+        />,
+        element,
+      ),
+    ).toWarnDev(
+      'Warning: Prop `style` did not match. Server: ' +
+        '"text-decoration: none; color: black; height: 10px;" Client: ' +
+        '"text-decoration:none;color:black;height:10px"',
+      {withoutStack: true},
+    );
+  });
+
   it('should throw rendering portals on the server', () => {
     const div = document.createElement('div');
     expect(() => {

packages/react-dom/src/client/ReactDOMComponent.js

@@ -999,12 +999,23 @@ export function diffHydratedProperties(
       } else if (propKey === STYLE) {
         // $FlowFixMe - Should be inferred as not undefined.
         extraAttributeNames.delete(propKey);
-        const expectedStyle = CSSPropertyOperations.createDangerousStringForStyles(
-          nextProp,
-        );
-        serverValue = domElement.getAttribute('style');
-        if (expectedStyle !== serverValue) {
-          warnForPropDifference(propKey, serverValue, expectedStyle);
+
+        // IE 11 parses & normalizes the style attribute as opposed to other
+        // browsers. It adds spaces and sorts the properties in some
+        // non-alphabetical order. Handling that would require sorting CSS
+        // properties in the client & server versions or applying
+        // `expectedStyle` to a temporary DOM node to read its `style` attribute
+        // normalized. Since it only affects IE, we're skipping style warnings
+        // in that browser completely in favor of doing all that work.
+        // See https://github.com/facebook/react/issues/11807
+        if (!document.documentMode) {
+          const expectedStyle = CSSPropertyOperations.createDangerousStringForStyles(
+            nextProp,
+          );
+          serverValue = domElement.getAttribute('style');
+          if (expectedStyle !== serverValue) {
+            warnForPropDifference(propKey, serverValue, expectedStyle);
+          }
         }
       } else if (isCustomComponentTag) {
         // $FlowFixMe - Should be inferred as not undefined.