Can one effectively edit a Front End Resource that is already loaded?

Question

A number of special definitions are loaded from .tr files on Front End initialization and are accessible via FrontEndResource. These are used among other things for various menus and toolsbars, e.g.:

FrontEndResource["FEBitmaps", "HomeIconHot"] // ToExpression

FrontEndResource["FEExpressions", "HelpViewerToolbar"] // CellPrint

FrontEndResource["ContextMenus", "GraphicsBox"]

FrontEndResource["ColorSchemeSelector"] // CellPrint

The .tr resource files can be edited to change these as I proposed for Can you make the new "Choose color scheme" helper larger? and Is it possible to insert new colour schemes into ColorData? It would be much nicer to be able to edit these after they are loaded from within Mathematica. One can Unprotect FrontEndResource and modify the definition but this does not actually change what is displayed in the Front End.

As a simple example I would like to make the Color Scheme Selector a little wider so that it does not have a pointless horizontal scroll bar on my system. I attempt:

Unprotect[FrontEndResource];

With[{FER := FrontEndResource["ColorSchemeSelector"]},
  FER = FER /. {180, Automatic} -> {195, Automatic};
]

The manually called resource is now wider:

FrontEndResource["ColorSchemeSelector"] // CellPrint

However the auto-complete popup for Color is not:

On examination this is not too surprising since the actual definition of FrontEndResource is:

FrontEndResource[name_] := 
  MathLink`CallFrontEnd[FrontEnd`Value[FEPrivate`FrontEndResource[name]]];

FrontEndResource[name_, sub_] := 
  MathLink`CallFrontEnd[FrontEnd`Value[FEPrivate`FrontEndResource[name, sub]]];

It seems logical that the Front End would make this lower level call directly, bypassing System`FrontEndResource. My problem is that I don't know how to redefine this FrontEnd`Value. Names finds a FrontEnd`SetValue which sounds promising but I haven't figured out how to use it.

How can I change this Front End Resource in a way that affects all appearances of the menu?

Answer 1

This is more comment than answer as you want in-memory modification, but it is possible to force the text resources to be reloaded. You do this with, e.g.,

FrontEndExecute@
 FrontEnd`FlushTextResourceCaches[]

So you can make a new text resource in $UserBaseDirectory and have that reload. For example, let's make a new TR for the file headers:

$headersTR =
  FrontEndExecute@
   FrontEnd`FindFileOnPath[
    "FileHeaders.tr",
    "PrivatePathsTextResources"
    ];
$newHeadersTR =
  StringReplace[$headersTR,
   $InstallationDirectory -> $UserBaseDirectory
   ];
CreateDirectory[DirectoryName@$newHeadersTR,
  CreateIntermediateDirectories -> True];
Export[
  $newHeadersTR,
  "
  @@resource PackageHeader
  (*?__?*)

  @|
  ",
  "Text"
  ];

Then reload the headers:

FrontEndExecute@FrontEnd`FlushTextResourceCaches[]
FrontEndResourceString["PackageHeader"]

"(*?__?*)
"

And that'll change the package header in all your auto-generated .m files.

Note that this isn't in-memory modification, but I'm not wholly these are always stored in memory, as sometimes deleting a file causes the FE to spit an error when you try to load a resource from that file.

On the other hand, something definitely is stored in memory. E.g., try deleting that new package header TR and loading the header again:

DeleteFile[$newHeadersTR]
FrontEndResourceString["PackageHeader"]

"(*?__?*)
"

So that's there until the cache is flushed.

Update:

Here's a way to get it to spit an error:

Export[
  $newHeadersTR,
  "
  @@resource PackageHeader
  (*?__?*)

  @|
  ",
  "Text"
  ];
FrontEndExecute@FrontEnd`FlushTextResourceCaches[]
DeleteFile[$newHeadersTR];
FrontEndResourceString["PackageHeader"]

$Failed

Clearly the FlushTextResourceCaches found that "PackageHeader" was in $newHeadersTR, but didn't load it. My guess would be that it got added to "ResourceMap.pbf" (see below) or something, but the load doesn't get performed until later.

Cache files:

Just as one last note on these caches, there're these files:

FileNames["ResourceMap.pbf",
 FileNameJoin@{$UserBaseDirectory, "FrontEnd"},
 Infinity
 ]

which are what actually get overridden when you call:

FrontEndExecute@
 FrontEnd`FlushTextResourceCaches[]

And they're some scrambled binary format, but if you look at them in plain-text view you see the file names where the resources are stored, e.g. I found:

"/Applications/Mathematica.app/Contents/AddOns/Applications/NotebookTemplating/FrontEnd/TextResources/NotebookTemplatingResources.tr"

in it.

So presumably this file gets used as the "ResourceMap" to the front-end to tell it from where to load resources it doesn't have in memory. That may also explain why deleting a cached resource file sometimes throws errors.