Bug 1668142 - Support AXDirectionPrevious in rotor with no start element. r=morgan

Depends on D91875

Differential Revision: https://phabricator.services.mozilla.com/D91878

accessible/mac/MOXSearchInfo.mm

@@ -77,9 +77,22 @@ using namespace mozilla::a11y;
   AccessibleOrProxy geckoRootAcc = [self rootGeckoAccessible];
   AccessibleOrProxy geckoStartAcc = [self startGeckoAccessible];
   Pivot p = Pivot(geckoRootAcc);
-  AccessibleOrProxy match = mSearchForward ? p.Next(geckoStartAcc, rule)
-                                           : p.Prev(geckoStartAcc, rule);
+  AccessibleOrProxy match;
+  if (mSearchForward) {
+    match = p.Next(geckoStartAcc, rule);
+  } else {
+    if (geckoRootAcc == geckoStartAcc) {
+      match = p.Last(rule);
+    } else {
+      match = p.Prev(geckoStartAcc, rule);
+    }
+  }
+
   while (!match.IsNull() && resultLimit != 0) {
+    if (!mSearchForward && match == geckoRootAcc) {
+      break;
+    }
+
     // we use mResultLimit != 0 to capture the case where mResultLimit is -1
     // when it is set from the params dictionary. If that's true, we want
     // to return all matches (ie. have no limit)

accessible/tests/browser/mac/browser_rotor.js

@@ -1521,5 +1521,23 @@ addAccessibleTask(
       ["p2"],
       "Result is next group sibling"
     );
+
+    searchPred = {
+      AXSearchKey: "AXAnyTypeSearchKey",
+      AXImmediateDescendantsOnly: 1,
+      AXResultsLimit: -1,
+      AXDirection: "AXDirectionPrevious",
+    };
+
+    results = searchRoot.getParameterizedAttributeValue(
+      "AXUIElementsForSearchPredicate",
+      NSDictionary(searchPred)
+    );
+
+    Assert.deepEqual(
+      results.map(r => r.getAttributeValue("AXDOMIdentifier")),
+      ["p2", "p1"],
+      "A reverse search should return groups in reverse"
+    );
   }
 );