[iOS WK2] API test EditorStateTests.ContentViewHasTextInContentEditab…

…leElement is a flaky failure

https://bugs.webkit.org/show_bug.cgi?id=177698

Reviewed by Ryosuke Niwa.

The WebKit2 API test EditorStateTests.ContentViewHasTextInContentEditableElement is currently hitting
intermittent failures on test runners. After inserting just an image in the editable element, we would expect
that -hasText should return NO because the text content is an empty string, but we find that -hasText is YES.
This is because we're bailing on an early return in computeEditableRootHasContentAndPlainText because the
EditorState's PostLayoutData contains non-zero characters near the selection, which is incorrect.

However, upon closer inspection, this is due to a latent bug in the charactersAroundPosition helper function.
This function attempts to compute characters before and after the current selection by initializing a Vector
of size 3 with the relevant character data, and then sets oneAfter, oneBefore and twoBefore to the UChar32
values in the vector. However, in the case where there are less than three characters, we end up assigning
the uninitialized values in the vector to one or more of oneAfter, oneBefore and twoBefore, which causes the
helper added in r222654 to bail early when it should not.

To fix this, we initialize the values in `characters` to 0 (which is the initial value for the 3 corresponding
members in the PostLayoutData struct). We also turn `characters` into a UChar32 array on the stack, to avoid the
heap allocations using a Vector<UChar32>.

No new tests; fixes a flaky API test.

* editing/VisibleUnits.cpp:
(WebCore::charactersAroundPosition):


Canonical link: https://commits.webkit.org/193967@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@222683 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WebCore/ChangeLog

@@ -1,3 +1,32 @@
+2017-09-30  Wenson Hsieh  <wenson_hsieh@apple.com>
+
+        [iOS WK2] API test EditorStateTests.ContentViewHasTextInContentEditableElement is a flaky failure
+        https://bugs.webkit.org/show_bug.cgi?id=177698
+
+        Reviewed by Ryosuke Niwa.
+
+        The WebKit2 API test EditorStateTests.ContentViewHasTextInContentEditableElement is currently hitting
+        intermittent failures on test runners. After inserting just an image in the editable element, we would expect
+        that -hasText should return NO because the text content is an empty string, but we find that -hasText is YES.
+        This is because we're bailing on an early return in computeEditableRootHasContentAndPlainText because the
+        EditorState's PostLayoutData contains non-zero characters near the selection, which is incorrect.
+
+        However, upon closer inspection, this is due to a latent bug in the charactersAroundPosition helper function.
+        This function attempts to compute characters before and after the current selection by initializing a Vector
+        of size 3 with the relevant character data, and then sets oneAfter, oneBefore and twoBefore to the UChar32
+        values in the vector. However, in the case where there are less than three characters, we end up assigning
+        the uninitialized values in the vector to one or more of oneAfter, oneBefore and twoBefore, which causes the
+        helper added in r222654 to bail early when it should not.
+
+        To fix this, we initialize the values in `characters` to 0 (which is the initial value for the 3 corresponding
+        members in the PostLayoutData struct). We also turn `characters` into a UChar32 array on the stack, to avoid the
+        heap allocations using a Vector<UChar32>.
+
+        No new tests; fixes a flaky API test.
+
+        * editing/VisibleUnits.cpp:
+        (WebCore::charactersAroundPosition):
+
 2017-09-30  Antti Koivisto  <antti@apple.com>
 
         Add makeWeakPtr for easier WeakPtr construction

Source/WebCore/editing/VisibleUnits.cpp

@@ -1892,7 +1892,7 @@ int distanceBetweenPositions(const VisiblePosition& vp, const VisiblePosition& o
 void charactersAroundPosition(const VisiblePosition& position, UChar32& oneAfter, UChar32& oneBefore, UChar32& twoBefore)
 {
     const int maxCharacters = 3;
-    Vector<UChar32> characters(maxCharacters);
+    UChar32 characters[maxCharacters] = { 0 };
 
     if (position.isNull() || isStartOfDocument(position))
         return;