[WIP] Implement sticky date separators

package.json

@@ -75,6 +75,7 @@
     "react-dnd-html5-backend": "^2.1.2",
     "react-dom": "^15.6.0",
     "react-gemini-scrollbar": "matrix-org/react-gemini-scrollbar#5e97aef",
+    "react-sticky": "^6.0.1",
     "sanitize-html": "^1.11.1",
     "text-encoding-utf-8": "^1.0.1",
     "ua-parser-js": "^0.7.10",

src/components/views/messages/DateSeparator.js

@@ -17,6 +17,7 @@ limitations under the License.
 import React from 'react';
 import { _t } from 'matrix-react-sdk/lib/languageHandler';
 import DateUtils from 'matrix-react-sdk/lib/DateUtils';
+import { Sticky } from 'react-sticky';
 
 function getdaysArray() {
 	return [
@@ -53,7 +54,17 @@ module.exports = React.createClass({
         }
 
         return (
-            <h2 className="mx_DateSeparator">{ label }</h2>
+            <Sticky relative={true} disableCompensation={true}>
+                {({style, isSticky, wasSticky, distanceFromTop}) => {
+                    return (
+                        <div className={"mx_DateSeparator_container mx_DateSeparator_container" + (isSticky ? '_sticky' : '')}
+                            style={{top: isSticky ? -distanceFromTop + "px" : 0}}
+                        >
+                            <h2 className="mx_DateSeparator">{ label }</h2>
+                        </div>
+                    );
+                }}
+            </Sticky>
         );
-    }
+    },
 });

src/skins/vector/css/vector-web/views/messages/_DateSeparator.scss

@@ -16,10 +16,26 @@ limitations under the License.
 
 .mx_DateSeparator {
     clear: both;
-    margin-top: 32px;
-    margin-bottom: 8px;
+    margin-top: 0px;
+    margin-bottom: 0px;
     margin-left: 63px;
+    padding-top: 5px;
     padding-bottom: 6px;
     border-bottom: 1px solid $primary-hairline-color;
 }
 
+.mx_DateSeparator_container {
+    margin-top: 27px;
+    margin-bottom: 8px;
+    background-color: $primary-bg-color;
+    z-index: 3;
+}
+
+.mx_DateSeparator_container_sticky {
+    position: relative;
+    border-bottom: 1px solid $primary-hairline-color;
+}
+
+.mx_DateSeparator_container_sticky .mx_DateSeparator {
+    border: 0px;
+}