a11y: Fix cursor-based text{Before,After}Offset

So far, qt_accTextBeforeOffsetHelper and
qt_accTextAfterOffsetHelper (used by
QAccessibleTextWidget and QAccessibleQuickItem)
were not consistently returning text items of
the given boundary type that is completely
*before* or *after* the given index, but
could e.g. return the word in whose
middle the offset is when using
QAccessible::WordBoundary.

This could for example break an assistive technology
feature of navigating through a text by word
if it relies on those methods.

Adjust the implementations to prevent that
from happening, by calling
QAccessible::qAccessibleTextBoundaryHelper
again with an index moved by one character
until either a result before/after the given
index is returned or the start/end of the text
has been reached.

Extend the existing QTextEdit a11y test
by a few cases that would previously fail.

(Note: Depending on the text granularity used,
not every character in the text is necessarily
considered part of any text item: E.g., when using
QAccessible::WordBoundary, space characters in between
words are not, at least not for the QTextCursor logic
as used in QTextEdit or qtdeclarative's QQuickTextEdit).

Fixes: QTBUG-140504
Task-number: QTBUG-139943
Change-Id: Ie6f0f2b2579237f42964d2498c818d1f02bf4bb8
Reviewed-by: Morten Johan Sørvig <[email protected]>

2 files changed, 32 insertions, 4 deletions

diff --git a/src/gui/accessible/qaccessiblehelper.cpp b/src/gui/accessible/qaccessiblehelper.cpp
index 40421ef329a..9ea72b1f6c9 100644
--- a/src/gui/accessible/qaccessiblehelper.cpp
+++ b/src/gui/accessible/qaccessiblehelper.cpp
@@ -57,13 +57,20 @@ QString qt_accTextBeforeOffsetHelper(const QAccessibleTextInterface &textInterfa
 {
     Q_ASSERT(startOffset);
     Q_ASSERT(endOffset);
+    *startOffset = *endOffset = -1;
 
     QTextCursor cursor = textCursor;
     cursor.setPosition(offset);
     std::pair<int, int> boundaries =
             QAccessible::qAccessibleTextBoundaryHelper(cursor, boundaryType);
-    cursor.setPosition(boundaries.first - 1);
-    boundaries = QAccessible::qAccessibleTextBoundaryHelper(cursor, boundaryType);
+    if (boundaries.second > offset) {
+        cursor.setPosition(boundaries.first);
+        while (boundaries.second > offset) {
+            if (!cursor.movePosition(QTextCursor::PreviousCharacter))
+                return QString();
+            boundaries = QAccessible::qAccessibleTextBoundaryHelper(cursor, boundaryType);
+        }
+    }
 
     *startOffset = boundaries.first;
     *endOffset = boundaries.second;
@@ -78,13 +85,20 @@ QString qt_accTextAfterOffsetHelper(const QAccessibleTextInterface &textInterfac
 {
     Q_ASSERT(startOffset);
     Q_ASSERT(endOffset);
+    *startOffset = *endOffset = -1;
 
     QTextCursor cursor = textCursor;
     cursor.setPosition(offset);
     std::pair<int, int> boundaries =
             QAccessible::qAccessibleTextBoundaryHelper(cursor, boundaryType);
-    cursor.setPosition(boundaries.second);
-    boundaries = QAccessible::qAccessibleTextBoundaryHelper(cursor, boundaryType);
+    if (boundaries.first <= offset) {
+        cursor.setPosition(boundaries.second);
+        while (boundaries.first <= offset) {
+            if (!cursor.movePosition(QTextCursor::NextCharacter))
+                return QString();
+            boundaries = QAccessible::qAccessibleTextBoundaryHelper(cursor, boundaryType);
+        }
+    }
 
     *startOffset = boundaries.first;
     *endOffset = boundaries.second;
diff --git a/tests/auto/other/qaccessibility/tst_qaccessibility.cpp b/tests/auto/other/qaccessibility/tst_qaccessibility.cpp
index 9a42c827504..2e92cdffada 100644
--- a/tests/auto/other/qaccessibility/tst_qaccessibility.cpp
+++ b/tests/auto/other/qaccessibility/tst_qaccessibility.cpp
@@ -1904,6 +1904,20 @@ void tst_QAccessibility::textEditTest()
         QCOMPARE(textIface->textAtOffset(15, QAccessible::LineBoundary, &startOffset, &endOffset), QString("How are you today?"));
         QCOMPARE(startOffset, 13);
         QCOMPARE(endOffset, 31);
+
+        QCOMPARE(textIface->textAfterOffset(3, QAccessible::WordBoundary, &startOffset, &endOffset),
+                 QString("world"));
+        QCOMPARE(
+                textIface->textBeforeOffset(8, QAccessible::WordBoundary, &startOffset, &endOffset),
+                QString("hello"));
+        // no more word before or after the last one
+        QCOMPARE(
+                textIface->textBeforeOffset(1, QAccessible::WordBoundary, &startOffset, &endOffset),
+                QString());
+        QCOMPARE(textIface->textAfterOffset(textIface->characterCount() - 1,
+                                            QAccessible::WordBoundary, &startOffset, &endOffset),
+                 QString());
+
         QCOMPARE(textIface->characterCount(), 48);
         QFontMetrics fm(edit.document()->defaultFont());
         QCOMPARE(textIface->characterRect(0).size(), QSize(fm.horizontalAdvance("h"), fm.height()));