[Webkit-unassigned] [Bug 55354] Assert that 0 <= offset <= lastOffsetInNode in Position's constructor, moveToPosition, and moveToOffset

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=55354





--- Comment #2 from Ryosuke Niwa <rniwa at webkit.org>  2011-03-03 00:07:59 PST ---
Now that the bug 51389 has been fixed, the only thing that prevents me from posting a patch for this bug is TypingCommand::forwardDeleteKeyPressed:

        if (!startingSelection().isRange() || selectionToDelete.base() != startingSelection().start())
            selectionAfterUndo = selectionToDelete;
        else {
            // It's a little tricky to compute what the starting selection would have been in the original document.
            // We can't let the VisibleSelection class's validation kick in or it'll adjust for us based on
            // the current state of the document and we'll get the wrong result.
            Position extent = startingSelection().end();
            if (extent.deprecatedNode() != selectionToDelete.end().deprecatedNode())
                extent = selectionToDelete.extent();
            else {
                int extraCharacters;
                if (selectionToDelete.start().deprecatedNode() == selectionToDelete.end().deprecatedNode())
                    extraCharacters = selectionToDelete.end().deprecatedEditingOffset() - selectionToDelete.start().deprecatedEditingOffset();
                else
                    extraCharacters = selectionToDelete.end().deprecatedEditingOffset();
@                extent = Position(extent.deprecatedNode(), extent.deprecatedEditingOffset() + extraCharacters, Position::PositionIsOffsetInAnchor);
            }
            selectionAfterUndo.setWithoutValidation(startingSelection().start(), extent);
        }

In running editing/undo/undo-forward-delete-boundary.html, we forward delete each letter in "wo<b>rd</b> and undo it.  When we forward delete the first letter, we get the following values at @:

(gdb) p startingSelection().showTreeForThis()
BODY    0x129859dc0
    #text    0x1298617c0 "\n"
    DIV    0x129862a60 CLASS=editing
        #text    0x1298604e0 "\n"
        SPAN    0x129860540
SE            #text    0x129848440 "This o"
            B    0x12985d950
                #text    0x129868c60 "rd "
            #text    0x12985bae0 "should be selected, since the test deleted it a character at a time and then did an undo."
        #text    0x12985bbc0 "\n"
    #text    0x129858560 "\n\n"
    SCRIPT    0x1298585c0
        #text    0x1298586e0 "\nrunEditingTest();\n"
start: legacy, offset, offset:5
end: legacy, offset, offset:6
$1 = void
Current language:  auto; currently c++
(gdb) p selectionToDelete.showTreeForThis()
BODY    0x129859dc0
    #text    0x1298617c0 "\n"
    DIV    0x129862a60 CLASS=editing
        #text    0x1298604e0 "\n"
        SPAN    0x129860540
SE            #text    0x129848440 "This o"
            B    0x12985d950
                #text    0x129868c60 "rd "
            #text    0x12985bae0 "should be selected, since the test deleted it a character at a time and then did an undo."
        #text    0x12985bbc0 "\n"
    #text    0x129858560 "\n\n"
    SCRIPT    0x1298585c0
        #text    0x1298586e0 "\nrunEditingTest();\n"
start: legacy, offset, offset:5
end: legacy, offset, offset:6
$2 = void

And we end up creating a position with offset 7 to incorporate "w" that has already been deleted.  In various parts of editing code, we do need to store such "invalid" positions for undo/redo operations.  Maybe that we need a variant of Position (PositionForUndo or UndoablePosition?) that tolerates such positions.

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