Bug 1901464 part 2: Refactor UiaText code to convert an array of TextLeafRanges to a SAFEARRAY of UiaTextRanges into a utility function. r=nlapre

This is currently only used by GetSelection, but it will be used by GetVisibleRanges in a subsequent patch.
There is a slight functionality change here: if there are no ranges, this returns an empty array.
GetSelection is unclear about what should be done here, but the documentation for GetVisibleRanges explicitly states an empty array should be returned, so that's what we do.
GetSelection previously left the SAFEARRAY pointer uninitialised in this case, which is definitely nasty and unsafe.

Differential Revision: https://phabricator.services.mozilla.com/D236089

Author: jcsteh

accessible/windows/uia/UiaText.cpp

@@ -11,8 +11,28 @@
 #include "TextLeafRange.h"
 #include "UiaTextRange.h"
 
-using namespace mozilla;
-using namespace mozilla::a11y;
+namespace mozilla::a11y {
+
+// Helpers
+
+static SAFEARRAY* TextLeafRangesToUiaRanges(
+    const nsTArray<TextLeafRange>& aRanges) {
+  // The documentation for GetSelection doesn't specify whether we should return
+  // an empty array or null if there are no ranges to return. However,
+  // GetVisibleRanges says that we should return an empty array, never null, so
+  // that's what we do.
+  // https://learn.microsoft.com/en-us/windows/win32/api/uiautomationcore/nf-uiautomationcore-itextprovider-getvisibleranges
+  SAFEARRAY* uiaRanges = SafeArrayCreateVector(VT_UNKNOWN, 0, aRanges.Length());
+  LONG indices[1] = {0};
+  for (const TextLeafRange& range : aRanges) {
+    // SafeArrayPutElement calls AddRef on the element, so we use a raw
+    // pointer here.
+    UiaTextRange* uiaRange = new UiaTextRange(range);
+    SafeArrayPutElement(uiaRanges, indices, uiaRange);
+    ++indices[0];
+  }
+  return uiaRanges;
+}
 
 // UiaText
 
@@ -40,17 +60,7 @@ UiaText::GetSelection(__RPC__deref_out_opt SAFEARRAY** aRetVal) {
       ranges.EmplaceBack(caret, caret);
     }
   }
-  if (!ranges.IsEmpty()) {
-    *aRetVal = SafeArrayCreateVector(VT_UNKNOWN, 0, ranges.Length());
-    LONG indices[1] = {0};
-    for (TextLeafRange& range : ranges) {
-      // SafeArrayPutElement calls AddRef on the element, so we use a raw
-      // pointer here.
-      UiaTextRange* uiaRange = new UiaTextRange(range);
-      SafeArrayPutElement(*aRetVal, indices, uiaRange);
-      ++indices[0];
-    }
-  }
+  *aRetVal = TextLeafRangesToUiaRanges(ranges);
   return S_OK;
 }
 
@@ -146,3 +156,5 @@ UiaText::get_SupportedTextSelection(
   }
   return S_OK;
 }
+
+}  // namespace mozilla::a11y