stylesheet - Forcing the front end to update style definitions

tl;dr

I need a way to apply style edits in stylesheets, even when I can't use cmd+Shift+E

ntl;wr

A while back I wrote a suite of stylesheet editing tools to automate operations I did in batch, which basically just finds all Cell[StyleData[style],___] cells. The tools work great, except for when I need to apply the edits I've performed.

For example, try this:

new = CreateDocument[Cell[BoxData@"input", "Input"],
   System`ClosingSaveDialog -> False];
SetOptions[new,
  StyleDefinitions ->
   Notebook[{
     Cell[StyleData[StyleDefinitions -> "Default.nb"]],
     Cell[StyleData["Input"]],
     Cell[BoxData@ToBoxes@Unevaluated@
         SetOptions[Cells[][[2]],
          Background -> LightBlue

          ],
      "Input",
      InitializationCell -> True],
     Cell[BoxData@ToBoxes@Unevaluated[
         SelectionMove[
          Cells[][[2]],
          All,
          Cell
          ];
         FrontEndTokenExecute@"ToggleShowExpression"; 

         FrontEndTokenExecute@"ToggleShowExpression";
         ],
      "Input"]
     },
    StyleDefinitions -> "PrivateStylesheetFormatting.nb"]
  ];
FrontEndTokenExecute[new, "EditStyleDefinitions"];
FrontEndTokenExecute["EvaluateInitialization"]

It'll apply the styling with SetOptions but doesn't update.

I can force updating using the "ToggleShowExpression" calls in the second input cell there, but that only works if I can actually move to the cell.

Usually I'm building styles in a notebook, so I can, but sometimes this doesn't work. Case in point, I've recently been playing with the hidden style notebooks that Mathematica opens to track style changes. E.g.

$DefaultStyleNotebook :=

 SelectFirst[FrontEndExecute@FrontEnd`ObjectChildren[$FrontEnd], 
  Quiet@NotebookFileName@# ===

    FileNameJoin@{$InstallationDirectory,
      "SystemFiles", "FrontEnd", "StyleSheets", "Default.nb"} &
  ]

That's the (usually hidden) notebook that sets all the default styles. Now I can set its properties using StylesheetEdit[style, ops], but the changes can't be applied because I can't use "ToggleShowExpression".

I've looked through many of the front-end packets, but can't find where whatever "cascade-update" type functionality the front end uses to apply these updates is hidden.

Can anyone help me out? Note that the real dream would be something that I can just evaluate in the kernel, but which preserves the CellObject. (i.e. no rewriting with NotebookWrite)

Example

As an example this is the sort of syntax I'm using:

SSEdit["Input", True,
 FontColor -> Red
 ]

where the True just means create a new Cell with StyleData["Input",...] if it doesn't exist in the style definitions notebook.

After application this is what we see:

And then we revert it like this:

SSEdit["Input", True,
 FontColor -> Inherited
 ]

Which we can see does indeed revert the change:

But here's the annoying code I have to use to get those changes to apply:

SSApplyEdits[cells : {__CellObject}] :=     
 With[{e = EvaluationCell[]},
  Do[
   SelectionMove[c, All, Cell,
    AutoScroll -> False];
   FrontEndTokenExecute[ParentNotebook@c,"ToggleShowExpression"];
   FrontEndTokenExecute[ParentNotebook@c,"ToggleShowExpression"];,
   {c, cells}
   ];

   SelectionMove[e, After, Cell]
   ];

Answer

Updating the style definition cascade after in-memory modification of a stylesheet using SetOptions

I've found that simple (and invalid) FrontEndExecute@ExportPacket[] doesn't work for this purpose but a valid ExportPacket works:

FrontEndExecute@ExportPacket[Notebook[{Cell[""]}], "BoundingBox"]; // AbsoluteTiming

{0.0135368, Null}

(instead of "BoundingBox" one can request "InputText" or "PlainText" what appears to be slightly faster).

How I tested this. First, I find the cell defining the "Input" style:

input = Select[Cells[$DefaultStyleNotebook], 
    First@NotebookRead[#] === StyleData["Input"] &][[1]];

Then I apply SetOptions on it:

SetOptions[input, {FontSize -> 16}]

Nothing is changed visually. Now after evaluating

FrontEndExecute@ExportPacket[Notebook[{Cell[""]}], "BoundingBox"];

The font size of the input cells changes...

---

Update: additional methods

It is sufficient just to create an invisible Notebook and immediately close it for forcing the style definitions cascade to update:

NotebookClose[CreateNotebook[Visible -> False]] // AbsoluteTiming

{0.0696042, Null}

Toggling dynamic updating twice also works (and for a stylesheet it should be safe since it shouldn't contain Dynamic elements)

Do[FrontEndExecute[
   FrontEndToken[$DefaultStyleNotebook, "ToggleDynamicUpdating"]], {2}] // AbsoluteTiming

{0.0126106, Null}