Fix datepicker DST bug (#2212)

* Fix datepicker DST bug. Closes #2204

This fix is borrowed from:
13885397de (diff-dd513a8bab7ad1033c8784c4a1b9ce15)

* Update NEWS.md

NEWS.md

@@ -47,6 +47,8 @@ This release features plot caching, an important new tool for improving performa
 
 * Fixed [#2142](https://github.com/rstudio/shiny/issues/2142): Dropping files on `fileInput`s stopped working on recent releases of Firefox. Thanks @dmenne for reporting! [#2203](https://github.com/rstudio/shiny/pull/2203)
 
+* Fixed [#2204](https://github.com/rstudio/shiny/issues/2204): `updateDateInput` could set the wrong date on days where DST begins. (Thanks @GaGaMan1101!) [#2212](https://github.com/rstudio/shiny/pull/2212)
+
 ### Documentation Updates
 
 * Addressed [#1864](https://github.com/rstudio/shiny/issues/1864) by changing `optgroup` documentation to use `list` instead of `c`. ([#2084](https://github.com/rstudio/shiny/pull/2084))

inst/www/shared/datepicker/js/bootstrap-datepicker.js

@@ -529,7 +529,17 @@
 		},
 
 		_utc_to_local: function(utc){
-			return utc && new Date(utc.getTime() + (utc.getTimezoneOffset()*60000));
+
+			if (!utc) return utc;
+
+			var local = new Date(utc.getTime() + (utc.getTimezoneOffset() * 60000));
+
+			if (local.getTimezoneOffset() != utc.getTimezoneOffset())
+			{
+				local = new Date(utc.getTime() + (local.getTimezoneOffset() * 60000));
+			}
+
+			return utc && local;
 		},
 		_local_to_utc: function(local){
 			return local && new Date(local.getTime() - (local.getTimezoneOffset()*60000));