a11y uia: Report UIA_StrikethroughStyleAttributeId

Implement support for getting the strikethrough
style (UIA attribute UIA_StrikethroughStyleAttributeId [1])
by checking for the corresponding IAccessible2
text attribute "text-line-through-type" [2] and
mapping the value accordingly if set.

Only report those attributes from the
QAccessibleTextInterface::attributes return value,
if they apply for the whole range of the
QWindowsUiaTextRangeProvider.

With this in place, the NVDA screen reader on
Windows announces "strikethrough" as expected
when asked to report the formatting information
(e.g. via NVDA+f shortcut) for the QTBUG-118106 example.

[1] https://learn.microsoft.com/en-us/windows/win32/winauto/uiauto-textattribute-ids
[2] https://wiki.linuxfoundation.org/accessibility/iaccessible2/textattributes

Task-number: QTBUG-118106
Change-Id: I2fa060bd3bf493227bba766385f34d224497784c
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

src/gui/accessible/windows/apisupport/uiatypes_p.h

@@ -66,6 +66,28 @@ enum TextPatternRangeEndpoint {
     TextPatternRangeEndpoint_End    = 1
 };
 
+enum TextDecorationLineStyle {
+    TextDecorationLineStyle_None = 0,
+    TextDecorationLineStyle_Single = 1,
+    TextDecorationLineStyle_WordsOnly = 2,
+    TextDecorationLineStyle_Double = 3,
+    TextDecorationLineStyle_Dot = 4,
+    TextDecorationLineStyle_Dash = 5,
+    TextDecorationLineStyle_DashDot = 6,
+    TextDecorationLineStyle_DashDotDot = 7,
+    TextDecorationLineStyle_Wavy = 8,
+    TextDecorationLineStyle_ThickSingle = 9,
+    TextDecorationLineStyle_DoubleWavy = 11,
+    TextDecorationLineStyle_ThickWavy = 12,
+    TextDecorationLineStyle_LongDash = 13,
+    TextDecorationLineStyle_ThickDash = 14,
+    TextDecorationLineStyle_ThickDashDot = 15,
+    TextDecorationLineStyle_ThickDashDotDot = 16,
+    TextDecorationLineStyle_ThickDot = 17,
+    TextDecorationLineStyle_ThickLongDash = 18,
+    TextDecorationLineStyle_Other = -1
+};
+
 enum CaretPosition {
     CaretPosition_Unknown           = 0,
     CaretPosition_EndOfLine         = 1,

src/plugins/platforms/windows/uiautomation/qwindowsuiatextrangeprovider.cpp

@@ -167,6 +167,15 @@ HRESULT STDMETHODCALLTYPE QWindowsUiaTextRangeProvider::GetAttributeValue(TEXTAT
         else
             setVariantI4(CaretPosition_Unknown, pRetVal);
         break;
+    case UIA_StrikethroughStyleAttributeId:
+    {
+        const QString value = valueForIA2Attribute(textInterface, QStringLiteral("text-line-through-type"));
+        if (value.isEmpty())
+            break;
+        const TextDecorationLineStyle uiaLineStyle = uiaLineStyleForIA2LineStyle(value);
+        setVariantI4(uiaLineStyle, pRetVal);
+        break;
+    }
     default:
         break;
     }
@@ -517,6 +526,42 @@ HRESULT QWindowsUiaTextRangeProvider::unselect()
     return S_OK;
 }
 
+// helper method to retrieve the value of the given IAccessible2 text attribute,
+// or an empty string if not set
+QString QWindowsUiaTextRangeProvider::valueForIA2Attribute(QAccessibleTextInterface *textInterface,
+                                                           const QString &key)
+{
+    Q_ASSERT(textInterface);
+
+    int startOffset;
+    int endOffset;
+    const QString attributes = textInterface->attributes(m_startOffset, &startOffset, &endOffset);
+    // don't report if attributes don't apply for the whole range
+    if (startOffset > m_startOffset || endOffset < m_endOffset)
+        return {};
+
+    for (auto attr : QStringTokenizer{attributes, u';'})
+    {
+        const QList<QStringView> items = attr.split(u':', Qt::SkipEmptyParts, Qt::CaseSensitive);
+        if (items.count() == 2 && items[0] == key)
+            return items[1].toString();
+    }
+
+    return {};
+}
+
+TextDecorationLineStyle QWindowsUiaTextRangeProvider::uiaLineStyleForIA2LineStyle(const QString &ia2LineStyle)
+{
+    if (ia2LineStyle == QStringLiteral("none"))
+        return TextDecorationLineStyle_None;
+    if (ia2LineStyle == QStringLiteral("single"))
+        return TextDecorationLineStyle_Single;
+    if (ia2LineStyle == QStringLiteral("double"))
+        return TextDecorationLineStyle_Double;
+
+    return TextDecorationLineStyle_Other;
+}
+
 QT_END_NAMESPACE
 
 #endif // QT_CONFIG(accessibility)

src/plugins/platforms/windows/uiautomation/qwindowsuiatextrangeprovider.h

@@ -42,6 +42,8 @@ public:
 
 private:
     HRESULT unselect();
+    QString valueForIA2Attribute(QAccessibleTextInterface *textInterface, const QString &key);
+    TextDecorationLineStyle uiaLineStyleForIA2LineStyle(const QString &ia2LineStyle);
     int m_startOffset;
     int m_endOffset;
 };