Re: [david.reitter@gmail.com: tool-bar: frame-local tool-bar-button-margin]

[Chong Yidong <cyd@stupidchicken.com>]

> Would someone please investigate this bug, and ack?
>
> From: David Reitter <david.reitter@gmail.com>
> Subject: tool-bar: frame-local tool-bar-button-margin
> To: emacs-pretest-bug@gnu.org
>
> Making tool-bar-button-margin a frame-local variable doesn't have the  
> desired effect.
> When several frames are open, a change to this variable will change  
> all tool-bars, not just the one belonging to the current frame.

The trouble is that tool-bar-button-margin is not a frame parameter.
The documentation for make-variable-frame-local says:

  Enable variable to have frame-local bindings.

  When a frame-local binding exists in the current frame,
  it is in effect whenever the current buffer has no buffer-local binding.
  A frame-local binding is actually a frame parameter value;
  thus, any given frame has a local binding for variable if it has
  a value for the frame parameter named variable.  Return variable.
  See `modify-frame-parameters' for how to set frame parameters.

The Elisp documentation is a little more explicit:

  Frame-local bindings are actually frame parameters: you create a
  frame-local binding in a specific frame by calling
  `modify-frame-parameters' and specifying the variable name as the
  parameter name...

  make-variable-frame-local:

     Enable the use of frame-local bindings for VARIABLE.  This does
     not in itself create any frame-local bindings for the variable;
     however, if some frame already has a value for VARIABLE as a frame
     parameter, that value automatically becomes a frame-local binding.

Using modify-frame-parameters followed by make-variable-frame-local, I
am indeed able to get frame-local values for tool-bar-button margin.

Probably the docstring for make-variable-frame-local should be
rephrased to make it clearer.