Allow a user to target "#anchor" by navigating to any prefix

Summary:
Ref T13410. We currently generate some less-than-ideal anchors in remarkup, but it's hard to change the algorithm without breaking stuff.

To mitigate this, allow `#xyz` to match any target on the page which begins with `xyz`. This means we can make anchors longer with no damage, and savvy users are free to shorten anchors to produce more presentation-friendly links.

Test Plan: Browsed to `#header-th`, was scrolled to `#header-three`, etc.

Maniphest Tasks: T13410

Differential Revision: https://secure.phabricator.com/D20820

resources/celerity/map.php

@@ -10,7 +10,7 @@ return array(
     'conpherence.pkg.css' => '3c8a0668',
     'conpherence.pkg.js' => '020aebcf',
     'core.pkg.css' => 'c69171e6',
-    'core.pkg.js' => '73a06a9f',
+    'core.pkg.js' => '6e5c894f',
     'differential.pkg.css' => '8d8360fb',
     'differential.pkg.js' => '0b037a4f',
     'diffusion.pkg.css' => '42c75c37',
@@ -506,7 +506,7 @@ return array(
     'rsrc/js/core/behavior-tokenizer.js' => '3b4899b0',
     'rsrc/js/core/behavior-tooltip.js' => '73ecc1f8',
     'rsrc/js/core/behavior-user-menu.js' => '60cd9241',
-    'rsrc/js/core/behavior-watch-anchor.js' => '0e6d261f',
+    'rsrc/js/core/behavior-watch-anchor.js' => '3972dadb',
     'rsrc/js/core/behavior-workflow.js' => '9623adc1',
     'rsrc/js/core/darkconsole/DarkLog.js' => '3b869402',
     'rsrc/js/core/darkconsole/DarkMessage.js' => '26cd4b73',
@@ -655,7 +655,7 @@ return array(
     'javelin-behavior-phabricator-tooltips' => '73ecc1f8',
     'javelin-behavior-phabricator-transaction-comment-form' => '2bdadf1a',
     'javelin-behavior-phabricator-transaction-list' => '9cec214e',
-    'javelin-behavior-phabricator-watch-anchor' => '0e6d261f',
+    'javelin-behavior-phabricator-watch-anchor' => '3972dadb',
     'javelin-behavior-pholio-mock-edit' => '3eed1f2b',
     'javelin-behavior-pholio-mock-view' => '5aa1544e',
     'javelin-behavior-phui-dropdown-menu' => '5cf0501a',
@@ -999,12 +999,6 @@ return array(
     '0d2490ce' => array(
       'javelin-install',
     ),
-    '0e6d261f' => array(
-      'javelin-behavior',
-      'javelin-stratcom',
-      'javelin-dom',
-      'javelin-vector',
-    ),
     '0eaa33a9' => array(
       'javelin-behavior',
       'javelin-dom',
@@ -1227,6 +1221,12 @@ return array(
       'javelin-install',
       'javelin-dom',
     ),
+    '3972dadb' => array(
+      'javelin-behavior',
+      'javelin-stratcom',
+      'javelin-dom',
+      'javelin-vector',
+    ),
     '398fdf13' => array(
       'javelin-behavior',
       'trigger-rule-editor',

webroot/rsrc/js/core/behavior-watch-anchor.js

@@ -8,52 +8,102 @@
 
 JX.behavior('phabricator-watch-anchor', function() {
 
-  var highlighted;
+  // When the user loads a page with an "#anchor" or changes the "#anchor" on
+  // an existing page, we try to scroll the page to the relevant location.
 
-  function highlight() {
+  // Browsers do this on their own, but we have some additional rules to try
-    highlighted && JX.DOM.alterClass(highlighted, 'anchor-target', false);
+  // to match anchors more flexibly and handle cases where an anchor is not
-    try {
+  // yet present in the document because something is still loading or
-      highlighted = JX.$('anchor-' + window.location.hash.replace('#', ''));
+  // rendering it, often via Ajax.
-    } catch (ex) {
-      highlighted = null;
-    }
-    highlighted && JX.DOM.alterClass(highlighted, 'anchor-target', true);
-  }
 
-  // Defer invocation so other listeners can update the document.
+  // Number of milliseconds we'll keep trying to find an anchor for.
-  function defer_highlight() {
+  var wait_max = 5000;
-    setTimeout(highlight, 0);
+
-  }
+  // Wait between retries.
+  var wait_ms = 100;
+
+  var target;
+  var retry_ms;
 
-  // In some cases, we link to an anchor but the anchor target ajaxes in
-  // later. If it pops in within the first few seconds, jump to it.
   function try_anchor() {
-    var anchor = window.location.hash.replace('#', '');
+    retry_ms = wait_max;
-    try {
+    seek_anchor();
-      // If the anchor exists, assume the browser handled the jump.
-      if (anchor) {
-        JX.$(anchor);
   }
-      defer_highlight();
+
-    } catch (e) {
+  function seek_anchor() {
-      var n = 50;
+    var anchor = window.location.hash.replace('#', '');
-      var try_anchor_again = function () {
+
+    if (!anchor.length) {
+      return;
+    }
+
+    var ii;
+    var node = null;
+
+    // When the user navigates to "#abc", we'll try to find a node with
+    // either ID "abc" or ID "anchor-abc".
+    var ids = [anchor, 'anchor-' + anchor];
+
+    for (ii = 0; ii < ids.length; ii++) {
+      try {
+        node = JX.$(ids[ii]);
+        break;
+      } catch (e) {
+        // Continue.
+      }
+    }
+
+    // If we haven't found a matching node yet, look for an "<a />" tag with
+    // a "name" attribute that has our anchor as a prefix. For example, you
+    // can navigate to "#cat" and we'll match "#cat-and-mouse".
+
+    if (!node) {
+      var anchor_nodes = JX.DOM.scry(document.body, 'a');
+      for (ii = 0; ii < anchor_nodes.length; ii++) {
+        if (!anchor_nodes[ii].name) {
+          continue;
+        }
+
+        if (anchor_nodes[ii].name.substring(0, anchor.length) === anchor) {
+          node = anchor_nodes[ii];
+          break;
+        }
+      }
+    }
+
+    // If we already have an anchor highlighted, unhighlight it and throw
+    // it away if it doesn't match the new target.
+    if (target && (target !== node)) {
+      JX.DOM.alterClass(target, 'anchor-target', false);
+      target = null;
+    }
+
+    // If we didn't find a matching anchor, try again soon. This allows
+    // rendering logic some time to complete Ajax requests and draw elements
+    // onto the page.
+    if (!node) {
+      if (retry_ms > 0) {
+        retry_ms -= wait_ms;
+        setTimeout(try_anchor, wait_ms);
+        return;
+      }
+    }
+
+    // If we've found a new target, highlight it.
+    if (target !== node) {
+      target = node;
+      JX.DOM.alterClass(target, 'anchor-target', true);
+    }
+
+    // Try to scroll to the new target.
     try {
-          var node = JX.$(anchor);
       var pos = JX.Vector.getPosWithScroll(node);
       JX.DOM.scrollToPosition(0, pos.y - 60);
-          defer_highlight();
     } catch (e) {
-          if (n--) {
+      // Ignore issues with scrolling the document.
-            setTimeout(try_anchor_again, 100);
-          }
-        }
-      };
-      try_anchor_again();
     }
   }
 
   JX.Stratcom.listen('hashchange', null, try_anchor);
   try_anchor();
-
 });