Bug 1822170 - Handle any kind of NSRanges provided to AXAttributedStringForRange. r=Jamie

This patch remedies 4 things:
1. Fix conversion from NSRange to GeckoTextMarkerRange. We were adding the start offset twice. Oops.
2. Clamp given range to actual text size. Since we are messing with the offset fields directly we need to do our own checks here.
3. Don't allow an infinite loop in CachedTextMarkerRange::AttributedText
4. Fix legacy Crop method to be able to take a text leaf.

Differential Revision: https://phabricator.services.mozilla.com/D172594

accessible/mac/CachedTextMarker.mm

@@ -327,6 +327,10 @@ NSAttributedString* CachedTextMarkerRange::AttributedText() const {
     TextLeafPoint attributesNext;
     do {
       attributesNext = start.FindTextAttrsStart(eDirNext, false);
+      if (attributesNext == start) {
+        MOZ_ASSERT_UNREACHABLE("Cannot proceed further in attribute run");
+        break;
+      }
       RefPtr<AccAttributes> attributes = start.GetTextAttributes();
       MOZ_ASSERT(attributes);
       if (attributes && !attributes->Equal(currentRun)) {

accessible/mac/LegacyTextMarker.mm

@@ -365,24 +365,23 @@ void LegacyTextMarkerRange::Select() const {
 }
 
 bool LegacyTextMarkerRange::Crop(Accessible* aContainer) {
-  LegacyTextMarker containerStart(aContainer, 0);
-  LegacyTextMarker containerEnd(aContainer, CharacterCount(aContainer));
+  LegacyTextMarkerRange containerRange(aContainer);
 
-  if (mEnd < containerStart || containerEnd < mStart) {
+  if (mEnd < containerRange.mStart || containerRange.mEnd < mStart) {
     // The range ends before the container, or starts after it.
     return false;
   }
 
-  if (mStart < containerStart) {
+  if (mStart < containerRange.mStart) {
     // If range start is before container start, adjust range start to
     // start of container.
-    mStart = containerStart;
+    mStart = containerRange.mStart;
   }
 
-  if (containerEnd < mEnd) {
+  if (containerRange.mEnd < mEnd) {
     // If range end is after container end, adjust range end to end of
     // container.
-    mEnd = containerEnd;
+    mEnd = containerRange.mEnd;
   }
 
   return true;

accessible/mac/mozTextAccessible.mm

@@ -415,9 +415,13 @@ static GeckoTextMarkerRange TextMarkerSubrange(Accessible* aAccessible,
 
   NSRange r = [aRange rangeValue];
   start.Offset() += r.location;
-  end.Offset() = start.Offset() + r.location + r.length;
+  end.Offset() = start.Offset() + r.length;
 
-  return GeckoTextMarkerRange(start, end);
+  textMarkerRange = GeckoTextMarkerRange(start, end);
+  // Crop range to accessible
+  textMarkerRange.Crop(aAccessible);
+
+  return textMarkerRange;
 }
 
 - (NSString*)moxStringForRange:(NSValue*)range {

accessible/tests/browser/mac/browser_attributed_text.js

@@ -61,6 +61,24 @@ addAccessibleTask(
       [" ", "#000000", "#ffffff", null, null, null, 16, null, null],
       ["test", "#0000ee", "#ffffff", 1, "#0000ee", null, 16, "a2", null],
     ]);
+
+    // Test different NSRange parameters for AXAttributedStringForRange
+    let worldLeaf = findAccessibleChildByID(accDoc, "a1").firstChild;
+    let wordStaticText = worldLeaf.nativeInterface.QueryInterface(
+      Ci.nsIAccessibleMacInterface
+    );
+    attributedText = wordStaticText.getParameterizedAttributeValue(
+      "AXAttributedStringForRange",
+      NSRange(4, 1)
+    );
+    is(attributedText.length, 1, "Last character is in single attribute run");
+    is(attributedText[0].string, "d", "Last character matches");
+
+    attributedText = wordStaticText.getParameterizedAttributeValue(
+      "AXAttributedStringForRange",
+      NSRange(5, 1)
+    );
+    is(attributedText.length, 0, "Range is past accessible bounds");
   }
 );
 

accessible/tests/browser/mac/browser_text_leaf.js

@@ -65,7 +65,7 @@ addAccessibleTask(
       NSRange(3, 6)
     );
 
-    is(str, "lo, this ", "AXStringForRange matches.");
+    is(str, "lo, th", "AXStringForRange matches.");
 
     let smallBounds = textLeaf.getParameterizedAttributeValue(
       "AXBoundsForRange",