Bug 1911505: Expose highlighted text to Mac a11y. r=morgan,eeejay

We do this via the undocumented AXHighlight attribute, as gleaned from the WebKit and Chromium source code.

Differential Revision: https://phabricator.services.mozilla.com/D218513

accessible/mac/MacUtils.mm

@@ -135,6 +135,12 @@ NSDictionary* StringAttributesFromAccAttributes(AccAttributes* aAttributes,
                        forKey:NSAccessibilityMarkedMisspelledTextAttribute];
         }
       }
+    } else if (iter.Name() == nsGkAtoms::mark) {
+      if (auto value = iter.Value<bool>()) {
+        if (*value) {
+          [attrDict setObject:@YES forKey:@"AXHighlight"];
+        }
+      }
     } else {
       nsAutoString valueStr;
       iter.ValueAsString(valueStr);

accessible/tests/browser/mac/browser.toml

@@ -13,6 +13,7 @@ support-files = [
   "!/accessible/tests/mochitest/letters.gif",
   "!/accessible/tests/mochitest/moz.png",
 ]
+prefs = ["dom.text_fragments.enabled=true"]
 
 ["browser_app.js"]
 https_first_disabled = true

accessible/tests/browser/mac/browser_attributed_text.js

@@ -163,3 +163,30 @@ addAccessibleTask(
     is(text, `hello  world${kEmbedChar}`, "Unattributed string is correct");
   }
 );
+
+// Test text fragment.
+addAccessibleTask(
+  `This is a test.`,
+  async (browser, accDoc) => {
+    const macDoc = accDoc.nativeInterface.QueryInterface(
+      Ci.nsIAccessibleMacInterface
+    );
+    const range = macDoc.getParameterizedAttributeValue(
+      "AXTextMarkerRangeForUnorderedTextMarkers",
+      [
+        macDoc.getAttributeValue("AXStartTextMarker"),
+        macDoc.getAttributeValue("AXEndTextMarker"),
+      ]
+    );
+    const attributedText = macDoc.getParameterizedAttributeValue(
+      "AXAttributedStringForTextMarkerRange",
+      range
+    );
+    is(attributedText.length, 3);
+    ok(!attributedText[0].AXHighlight);
+    ok(attributedText[1].AXHighlight);
+    is(attributedText[1].string, "test");
+    ok(!attributedText[2].AXHighlight);
+  },
+  { urlSuffix: "#:~:text=test" }
+);