bug#33601: 26; Add macro `with-hook-added'

[Alan Mackenzie]

Hello, Drew.

In article <mailman.5097.1543862895.1284.bug-gnu-emacs@gnu.org> you wrote:
> Enhancement request: Please consider adding a macro such as this, to
> facilitate temporary use of a hook function.

> (defmacro with-hook-added (hook function &rest body)
>   "Evaluate forms in BODY with FUNCTION added to HOOK, then remove FUNCTION."
>   (declare (indent 1) (debug t))
>   `(unwind-protect (progn (add-hook ',hook ',function) ,@body)
>      (remove-hook ',hook ',function)))

Just a big point: you need to test whether FUNCTION is already on HOOK
at the start, and if so, not remove it at the end.

Apologies if somebody else has already pointed this out.

> In GNU Emacs 26.1 (build 1, x86_64-w64-mingw32)
>  of 2018-05-30
> Repository revision: 07f8f9bc5a51f5aa94eb099f3e15fbe0c20ea1ea
> Windowing system distributor `Microsoft Corp.', version 10.0.16299
> Configured using:
>  `configure --without-dbus --host=x86_64-w64-mingw32
>  --without-compress-install 'CFLAGS=-O2 -static -g3''

-- 
Alan Mackenzie (Nuremberg, Germany).