Tabs: Properly handle decoded/encoded anchor hashes & panel IDs

Prior to jQuery UI 1.14.1, hashes in anchor hrefs were used directly. In
gh-2307, that was changed - by decoding - to support more complex IDs, e.g.
containing emojis which are automatically encoded in `anchor.hash`.
Unfortunately, that broke cases where the panel ID is decoded as well.

It turns out the spec mandates checking both. In the "scrolling to a fragment"
section of the HTML spec[^1]. That uses a concept of document's indicated
part[^2]. Slightly below there's an algorithm to compute the indicated part[^3].
The interesting parts are steps 4 to 9:
4. Let potentialIndicatedElement be the result of finding a potential
   indicated element given document and fragment.
5. If potentialIndicatedElement is not null, then return
   potentialIndicatedElement.
6. Let fragmentBytes be the result of percent-decoding fragment.
7. Let decodedFragment be the result of running UTF-8 decode without BOM on
   fragmentBytes.
8. Set potentialIndicatedElement to the result of finding a potential indicated
   element given document and decodedFragment.
9. If potentialIndicatedElement is not null, then return
   potentialIndicatedElement.

First, in steps 4-5, the algorithm tries the hash as-is, without decoding. Then,
if one is not found, the same is attempted with a decoded hash.

This change replicates this logic by first trying the hash as-is and then
decoding it.

Fixes gh-2344
Closes gh-2345
Ref gh-2307

[^1]: https://html.spec.whatwg.org/#scrolling-to-a-fragment
[^2]: https://html.spec.whatwg.org/#the-indicated-part-of-the-document
[^3]: https://html.spec.whatwg.org/#select-the-indicated-part

tests/unit/tabs/core.js

@@ -773,4 +773,55 @@ QUnit.test( "URL-based auth with local tabs (gh-2213)", function( assert ) {
 	}
 } );
 
+( function() {
+	function getVerifyTab( assert, element ) {
+		return function verifyTab( index ) {
+			assert.strictEqual(
+				element.tabs( "option", "active" ),
+				index,
+				"should set the active option to " + index );
+			assert.strictEqual(
+				element.find( "[role='tabpanel']:visible" ).text().trim(),
+				"Tab " + ( index + 1 ),
+				"should set the panel to 'Tab " + ( index + 1 ) + "'" );
+		};
+	}
+
+	QUnit.test( "href encoding/decoding (gh-2344)", function( assert ) {
+		assert.expect( 12 );
+
+		location.hash = "#tabs-2";
+
+		var i,
+			element = $( "#tabs10" ).tabs(),
+			tabLinks = element.find( "> ul a" ),
+			verifyTab = getVerifyTab( assert, element );
+
+		for ( i = 0; i < tabLinks.length; i++ ) {
+			tabLinks.eq( i ).trigger( "click" );
+			verifyTab( i );
+		}
+
+		location.hash = "";
+	} );
+
+	QUnit.test( "href encoding/decoding on init (gh-2344)", function( assert ) {
+		assert.expect( 12 );
+
+		var i,
+			element = $( "#tabs10" ),
+			tabLinks = element.find( "> ul a" ),
+			verifyTab = getVerifyTab( assert, element );
+
+		for ( i = 0; i < tabLinks.length; i++ ) {
+			location.hash = tabLinks.eq( i ).attr( "href" );
+			element.tabs();
+			verifyTab( i );
+			element.tabs( "destroy" );
+		}
+
+		location.hash = "";
+	} );
+} )();
+
 } );

tests/unit/tabs/tabs.html

@@ -125,6 +125,35 @@
 	<div id="tabs9-1"></div>
 </div>
 
+<div id="tabs10">
+	<ul>
+		<li><a href="#tabs-1">1</a></li>
+		<li><a href="#tabs-2">2</a></li>
+		<li><a href="#%EF%B8%8F">3</a></li>
+		<li><a href="#🤗">4</a></li>
+		<li><a href="#😅">5</a></li>
+		<li><a href="#%25F0%259F%25A4%25AD">6</a></li>
+	</ul>
+	<div id="tabs-1">
+		<p>Tab 1</p>
+	</div>
+	<div id="tabs-2">
+		<p>Tab 2</p>
+	</div>
+	<div id="%EF%B8%8F">
+		<p>Tab 3</p>
+	</div>
+	<div id="🤗">
+		<p>Tab 4</p>
+	</div>
+	<div id="%F0%9F%98%85">
+		<p>Tab 5</p>
+	</div>
+	<div id="%F0%9F%A4%AD">
+		<p>Tab 6</p>
+	</div>
+</div>
+
 </div>
 </body>
 </html>

ui/widgets/tabs.js

@@ -114,18 +114,31 @@ $.widget( "ui.tabs", {
 	_initialActive: function() {
 		var active = this.options.active,
 			collapsible = this.options.collapsible,
-			locationHashDecoded = decodeURIComponent( location.hash.substring( 1 ) );
+			locationHash = location.hash.substring( 1 ),
+			locationHashDecoded = decodeURIComponent( locationHash );
 
 		if ( active === null ) {
 
 			// check the fragment identifier in the URL
-			if ( locationHashDecoded ) {
+			if ( locationHash ) {
 				this.tabs.each( function( i, tab ) {
-					if ( $( tab ).attr( "aria-controls" ) === locationHashDecoded ) {
+					if ( $( tab ).attr( "aria-controls" ) === locationHash ) {
 						active = i;
 						return false;
 					}
 				} );
+
+				// If not found, decode the hash & try again.
+				// See the comment in `_processTabs` under the `_isLocal` check
+				// for more information.
+				if ( active === null ) {
+					this.tabs.each( function( i, tab ) {
+						if ( $( tab ).attr( "aria-controls" ) === locationHashDecoded ) {
+							active = i;
+							return false;
+						}
+					} );
+				}
 			}
 
 			// Check for a tab marked active via a class
@@ -423,9 +436,24 @@ $.widget( "ui.tabs", {
 
 			// Inline tab
 			if ( that._isLocal( anchor ) ) {
-				selector = decodeURIComponent( anchor.hash );
+
+				// The "scrolling to a fragment" section of the HTML spec:
+				// https://html.spec.whatwg.org/#scrolling-to-a-fragment
+				// uses a concept of document's indicated part:
+				// https://html.spec.whatwg.org/#the-indicated-part-of-the-document
+				// Slightly below there's an algorithm to compute the indicated
+				// part:
+				// https://html.spec.whatwg.org/#the-indicated-part-of-the-document
+				// First, the algorithm tries the hash as-is, without decoding.
+				// Then, if one is not found, the same is attempted with a decoded
+				// hash. Replicate this logic.
+				selector = anchor.hash;
 				panelId = selector.substring( 1 );
 				panel = that.element.find( "#" + CSS.escape( panelId ) );
+				if ( !panel.length ) {
+					panelId = decodeURIComponent( panelId );
+					panel = that.element.find( "#" + CSS.escape( panelId ) );
+				}
 
 			// remote tab
 			} else {