Bug 1869966 part 3: When calculating a DOM point from a TextLeafPoint for a non-text node, use the child index within the parent, not an offset within the node itself. r=eeejay

For text nodes, DOM points use the character offset within the node itself, just like accessibility does.
For non-text nodes, DOM points use the child index within the parent to specify the position before or after the node.
Previously, TextLeafPoint::ToDOMPoint always used an offset within the node itself.
This meant that when the (exclusive) end point of a range was an image, we converted to a DOM point of offset 0 within the image.
As far as DOM is concerned, this includes the image.
This patch adjusts ToDOMPoint as appropriate.

As part of this, ToDOMPoint now returns a uint32_t instead of an int32_t.
This is because DOM offsets are actually uint32_t and calculating int32_t child indices is deprecated.

Differential Revision: https://phabricator.services.mozilla.com/D247873

accessible/base/TextLeafRange.cpp

@@ -536,7 +536,7 @@ static dom::Selection* GetDOMSelection(const nsIContent* aStartContent,
   return startFrameSel ? &startFrameSel->NormalSelection() : nullptr;
 }
 
-std::pair<nsIContent*, int32_t> TextLeafPoint::ToDOMPoint(
+std::pair<nsIContent*, uint32_t> TextLeafPoint::ToDOMPoint(
     bool aIncludeGenerated) const {
   if (!(*this) || !mAcc->IsLocal()) {
     MOZ_ASSERT_UNREACHABLE("Invalid point");
@@ -573,9 +573,23 @@ std::pair<nsIContent*, int32_t> TextLeafPoint::ToDOMPoint(
     }
   }
 
-  if (!mAcc->IsTextLeaf() && !mAcc->IsHTMLBr() && !mAcc->HasChildren()) {
-    // If this is not a text leaf it can be an empty editable container,
-    // whitespace, or an empty doc. In any case, the offset inside should be 0.
+  if (mAcc->IsTextLeaf()) {
+    // For text nodes, DOM uses a character offset within the node.
+    return {content, RenderedToContentOffset(mAcc->AsLocal(), mOffset)};
+  }
+
+  if (!mAcc->IsHyperText()) {
+    // For non-text nodes (e.g. images), DOM points use the child index within
+    // the parent.
+    nsIContent* parent = content->GetParent();
+    MOZ_ASSERT(parent);
+    auto childIndex = parent->ComputeIndexOf(content);
+    MOZ_ASSERT(childIndex);
+    return {parent, *childIndex};
+  }
+
+  // This could be an empty editable container, whitespace or an empty doc. In
+  // any case, the offset inside should be 0.
   MOZ_ASSERT(mOffset == 0);
 
   if (RefPtr<TextControlElement> textControlElement =
@@ -592,9 +606,6 @@ std::pair<nsIContent*, int32_t> TextLeafPoint::ToDOMPoint(
   return {content, 0};
 }
 
-  return {content, RenderedToContentOffset(mAcc->AsLocal(), mOffset)};
-}
-
 static bool IsLineBreakContinuation(nsTextFrame* aContinuation) {
   // A fluid continuation always means a new line.
   if (aContinuation->HasAnyStateBits(NS_FRAME_IS_FLUID_CONTINUATION)) {

accessible/base/TextLeafRange.h

@@ -188,7 +188,7 @@ class TextLeafPoint final {
   /**
    * Translate given TextLeafPoint into a DOM point.
    */
-  MOZ_CAN_RUN_SCRIPT std::pair<nsIContent*, int32_t> ToDOMPoint(
+  MOZ_CAN_RUN_SCRIPT std::pair<nsIContent*, uint32_t> ToDOMPoint(
       bool aIncludeGenerated = true) const;
 
  private:

accessible/tests/browser/windows/ia2/browser_textSelectionContainer.js

@@ -21,7 +21,7 @@ function checkSelection(root, ranges) {
  * Test IAccessibleTextSelectionContainer::setSelections.
  */
 addAccessibleTask(
-  `<p id="p">ab<a id="link" href="/">cd</a>ef</p>`,
+  `<p id="p">ab<a id="link" href="/">cd</a>ef<img id="img" src="https://example.com/a11y/accessible/tests/mochitest/moz.png" alt="g"></p>`,
   async function testSetSelections(browser, docAcc) {
     docAcc.QueryInterface(nsIAccessibleText);
     await runPython(`
@@ -66,6 +66,21 @@ addAccessibleTask(
     await selected;
     checkSelection(docAcc, [[link, 1, p, 4]]);
 
+    info("Selecting f");
+    selected = waitForEvent(EVENT_TEXT_SELECTION_CHANGED, p);
+    await runPython(`
+      docSel.setSelections(1, byref(IA2TextSelection(p, 4, p, 5, False)))
+    `);
+    await selected;
+    checkSelection(docAcc, [[p, 4, p, 5]]);
+    // DOM treats an end point of (img, 0) as including the image. Ensure we
+    // used a DOM child index.
+    await invokeContentTask(browser, [], () => {
+      const sel = content.getSelection();
+      is(sel.focusNode.id, "p", "DOM selection focus node correct");
+      is(sel.focusOffset, 3, "DOM selection focus offset correct");
+    });
+
     info("Selecting a, c");
     selected = waitForEvent(EVENT_TEXT_SELECTION_CHANGED, link);
     await runPython(`