mu4e: by default, make changing to current context a no-op

Update mu4e-context-switch to not call the enter/leave functions when
'changing' to the current context. However, calling those functions (if
defined) can be force through a prefix arg. Document this.

Make mu4e-context-determine recognize 'policies', i.e. what to do when
no context matches. This part is WIP.

mu4e/mu4e-compose.el

@@ -372,8 +372,8 @@ tempfile)."
   (put 'mu4e-compose-parent-message 'permanent-local t)
   (let ((context (mu4e-context-determine mu4e-compose-parent-message)))
     (if context
-        (mu4e-context-switch (mu4e-context-name context))
-      (when mu4e-contexts (mu4e-context-switch))))
+      (mu4e-context-switch nil (mu4e-context-name context))
+      (when mu4e-contexts (mu4e-context-switch nil))))
   (run-hooks 'mu4e-compose-pre-hook)
 
   ;; this opens (or re-opens) a messages with all the basic headers set.

mu4e/mu4e-context.el

@@ -59,22 +59,35 @@ for the message replied to or forwarded, and nil otherwise. Before composing a n
   ;; if it matches, nil otherwise
   vars)                     ;; alist of variables.
 
-(defun mu4e-context-switch (&optional name)
+(defun mu4e~context-ask-user (prompt)
+  "Let user choose some context based on its name."
+  (when mu4e-contexts
+    (let* ((names (map 'list (lambda (context) (cons (mu4e-context-name context) context))
+		    mu4e-contexts))
+	    (context (mu4e-read-option prompt names)))
+      (or context (mu4e-error "No such context")))))
+
+(defun mu4e-context-switch (&optional force name)
   "Switch context to a context with NAME which is part of
-`mu4e-contexts'; if NAME is nil, query user."
-  (interactive)
+`mu4e-contexts'; if NAME is nil, query user.
+
+If the new context is the same and the current context, only
+switch (run associated functions) when prefix argument FORCE is
+non-nil."
+  (interactive "P")
   (unless mu4e-contexts
     (mu4e-error "No contexts defined"))
   (let* ((names (map 'list (lambda (context)
 			     (cons (mu4e-context-name context) context))
 		  mu4e-contexts))
 	  (context
-	    (if name (cdr-safe  (assoc name names))
-	      (mu4e-read-option "Switch to context: " names))))
+	    (if name
+	      (cdr-safe (assoc name names))
+	      (mu4e~context-ask-user "Switch to context: "))))
     (unless context (mu4e-error "No such context"))
-   
-    ;; leave the current context
-    (when (and mu4e~context-current (mu4e-context-leave-func mu4e~context-current))
+    ;; if new context is same as old one one switch with FORCE is set.
+    (when (or force (not (eq context (mu4e-context-current))))
+      (when (and (mu4e-context-current) (mu4e-context-leave-func mu4e~context-current))
 	(funcall (mu4e-context-leave-func mu4e~context-current)))
       ;; enter the new context
       (when (mu4e-context-enter-func context)
@@ -84,7 +97,7 @@ for the message replied to or forwarded, and nil otherwise. Before composing a n
 		  (set (car cell) (cdr cell)))
 	  (mu4e-context-vars context)))
       (setq mu4e~context-current context)
-    (mu4e-message "Switched context to %s" (mu4e-context-name context))
+      (mu4e-message "Switched context to %s" (mu4e-context-name context)))
     context))
 
 (defun mu4e-context-autoselect ()
@@ -95,19 +108,26 @@ match, return the first."
    (mu4e-context-switch
      (mu4e-context-name  (mu4e-context-determine nil 'pick-first)))))
 
-(defun mu4e-context-determine (msg &optional pick-first)
+(defun mu4e-context-determine (msg &optional policy)
   "Return the first context with a match-func that returns t. MSG
 points to the plist for the message replied to or forwarded, or
 nil if there is no such MSG; similar to what
 `mu4e-compose-pre-hook' does.
 
-If there are contexts but none match, return nil, unless
-  PICK-FIRST is non-nil, in which case return the first context."
+POLICY determines what to do if there are contexts but none match. The following
+are supported:
+- pick-first: pick the first of the contexts available
+- ask: ask the user
+- otherwise, return nil. Effectively, this leaves the current context in place."
   (when mu4e-contexts
     (or (find-if (lambda (context)
 		   (and (mu4e-context-match-func context)
 		     (funcall (mu4e-context-match-func context) msg))) mu4e-contexts)
-      (when pick-first (car mu4e-contexts)))))
+      ;; no context found
+      (case policy
+	(pick-first (car mu4e-contexts))
+	(ask (mu4e~context-ask-user "Select context: "))
+	(otherwise nil)))))
 
 (provide 'mu4e-context)
  

mu4e/mu4e.texi

@@ -1809,7 +1809,8 @@ Note - in the @ref{Headers view} you may see the 'friendly name' for a
 list; however, when searching you need the real name. You can see the
 real name for a mailing list from the friendly name's tool-tip.
 
-@item Get messages with a subject soccer, Socrates, society, ...; note that the '*'-wildcard can only appear as a term's rightmost character:
+@item Get messages with a subject soccer, Socrates, society, ...; note that
+the '*'-wildcard can only appear as a term's rightmost character:
 @verbatim
 subject:soc*
 @end verbatim
@@ -2358,13 +2359,20 @@ when starting; see the discussion in the previous section.
 
 Couple of notes:
 @itemize
-@item You can manually switch the focus use @code{M-x mu4e-context-switch}, by default bound to @code{;} in headers, view and main mode. The current focus appears in the mode-line.
-@item The function @code{mu4e-context-current} returns the current-context; the current context is also visiable in the mode-line when in headers, view or main mode.
-@item You can set any kind of variable; including settings for mail servers etc. However, settings like @code{mu4e-maildir} and @code{mu4e-mu-home} are not changeable after they have been set without quiting @t{mu4e} first.
-@item @code{leave-func} (if defined) for the context we are leaving, is invoked before the @code{enter-func} (if defined) of the context we are entering.
+@item You can manually switch the focus use @code{M-x mu4e-context-switch}, by default bound to @kbd{;} in headers, view and main mode.
+The current focus appears in the mode-line.
+@item Normally, @code{M-x mu4e-context-switch} does not call the enter/leave functions if the 'new' context is the same as the old one.
+However, with a prefix-argument (@kbd{C-u}), you can force @t{mu4e} to call
+those function even in that case.
+@item The function @code{mu4e-context-current} returns the current-context; the current context is also visiable in the mode-line when in
+headers, view or main mode.
+@item You can set any kind of variable; including settings for mail servers etc. However, settings like @code{mu4e-maildir}
+and @code{mu4e-mu-home} are not changeable after they have been set without quiting @t{mu4e} first.
+@item @code{leave-func} (if defined) for the context we are leaving, is invoked before the @code{enter-func} (if defined) of the
+context we are entering.
 @item @code{enter-func} (if defined) is invoked before setting the variables.
 @item @code{match-func} (if defined) is invoked just before @code{mu4e-compose-pre-hook}.
-@item Finally, be careful to get the quotations right -- backticks, single quotes and commas and note the '.' between variable name and value.
+@item Finally, be careful to get the quotations right -- backticks, single quotes and commas and note the '.' between variable name and its value.
 @end itemize
 
 @node Some context tricks
@@ -3508,7 +3516,8 @@ five arguments, following @t{completing-read}. The default value is
 @t{ido-completing-read}; to use emacs's default behaviour, set the
 variable to @t{completing-read}. Helm users can use the same value, and
 by enabling @t{helm-mode} use helm-style completion.
-@item @emph{I have a lot of Maildir folders, so regenerating them each time makes things slow. What can I do?}
+@item @emph{I have a lot of Maildir folders, so regenerating them each time makes
+things slow. What can I do?}
 Set @code{mu4e-cache-maildir-list} to @code{t} (but make sure to read
 its docstring).
 
@@ -3540,7 +3549,8 @@ messages}.
 like Gmail does?} Yes -- see @ref{Including related messages}.
 @item @emph{There seem to be a lot of duplicate messages -- how can I get rid
 of them?} See @ref{Skipping duplicates}.
-@item @emph{How can I use the @t{eww} browser to view rich-text messages?} See @ref{Html2text functions}.
+@item @emph{How can I use the @t{eww} browser to view rich-text messages?}
+See @ref{Html2text functions}.
 @item @emph{Some messages are almost unreadable in emacs - can I view them in
 an external web browser?} Indeed, airlines often send messages that
 heavily depend on html and are hard to digest inside emacs. Fortunately,