bug#16111: (erc-current-logfile buf) behavior differs to with-current-buffer buf

[Ivan Shmakov <ivan@siamics.net>]

Package:  emacs
Severity: minor

	My guess is that the results of (erc-current-logfile buffer) and
	(with-current-buffer buffer (erc-current-logfile)) were intended
	to be the same.  However, as the function references the session
	buffer-local variables (erc-session-server, erc-session-port,
	and, indirectly, erc-server-current-nick and erc-server-process)
	/without/ switching to the buffer given, the results are
	somewhat undefined.

(defun erc-current-logfile (&optional buffer)
  "Return the logfile to use for BUFFER.
If BUFFER is nil, the value of `current-buffer' is used.
This is determined by `erc-generate-log-file-name-function'.
The result is converted to lowercase, as IRC is case-insensitive"
  (unless buffer (setq buffer (current-buffer)))
  (let ((target (or (buffer-name buffer) (erc-default-target)))
	(nick (erc-current-nick))
	(server erc-session-server)
	(port erc-session-port))
    …))

	(There, it may make sense to enclose the most part of the code
	within a with-current-buffer form.)

	This may show no symptoms as long as erc-save-buffer-in-logs is
	called in either of the buffers belonging to the same session,
	but I’m in doubt that erc-log-save-all-buffers (which may run as
	part of kill-emacs-hook) will behave sensible in general.

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