Ensure that user-mail-address always has a value

* lisp/startup.el (user-mail-address): Initialize in the normal way.
(command-line): Reset user-mail-address if needed using
standard custom machinery.
* lisp/mail/feedmail.el (feedmail-fiddle-from):
* lisp/mail/rmail.el (rmail-unknown-mail-followup-to):
* lisp/mail/rmailsum.el (rmail-header-summary):
Simplify now that user-mail-address is always set.
; * doc/lispref/os.texi (System Environment): Remove fixme comment.

doc/lispref/os.texi

@@ -941,8 +941,6 @@ If this variable is non-@code{nil}, it is used instead of
 @code{system-name} for purposes of generating email addresses.  For
 example, it is used when constructing the default value of
 @code{user-mail-address}.  @xref{User Identification}.
-@c FIXME sounds like should probably give this a :set-after and some
-@c custom-initialize-delay voodoo.
 @end defopt
 
 @deffn Command getenv var &optional frame

lisp/mail/feedmail.el

@@ -2759,24 +2759,17 @@ return that value."
   (cond
    ;; nil means do nothing
    ((eq nil feedmail-from-line) nil)
-   ;; t is the same a using the default computation, so compute it and recurse
+   ;; t is the same as using the default computation, so compute it and recurse
    ;; user-full-name suggested by kpc@ptolemy.arc.nasa.gov (=Kimball Collins)
    ;; improvement using user-mail-address suggested by
    ;;   gray@austin.apc.slb.com (Douglas Gray Stephens)
-   ;; improvement using mail-host-address suggested by "Jason Eisner" <jason@cs.jhu.edu>
-   ;; ((this situation really is hopeless, though)
    ((eq t feedmail-from-line)
     (let ((feedmail-from-line
-	   (let ((at-stuff
-		  (if (> (length user-mail-address) 0)
-		      user-mail-address
-		    (concat (user-login-name) "@"
-			    (or mail-host-address (system-name))))))
-	     (cond
-	      ((eq mail-from-style nil) at-stuff)
-	      ((eq mail-from-style 'parens) (concat at-stuff " (" (user-full-name) ")"))
-	      ((eq mail-from-style 'angles) (concat "\"" (user-full-name) "\" <" at-stuff ">"))
-	      ))))
+	   (cond
+	    ((eq mail-from-style nil) user-mail-address)
+	    ((eq mail-from-style 'parens) (concat user-mail-address " (" (user-full-name) ")"))
+	    ((eq mail-from-style 'angles) (concat "\"" (user-full-name) "\" <" user-mail-address ">"))
+	    )))
       (feedmail-fiddle-from)))
 
    ;; if it's a string, simply make a fiddle-plex out of it and recurse

lisp/mail/rmail.el

@@ -2665,12 +2665,7 @@ Ask the user whether to add that list name to `mail-mailing-lists'."
 			      (concat "^\\("
 				      (regexp-quote (user-login-name))
 				      "\\($\\|@\\)\\|"
-				      (regexp-quote
-				       (if (> (length user-mail-address) 0)
-					   user-mail-address
-					 (concat (user-login-name) "@"
-						 (or mail-host-address
-						     (system-name)))))
+				      (regexp-quote user-mail-address)
 				      "\\>\\)"))
 			  addr))
 			(y-or-n-p

lisp/mail/rmailsum.el

@@ -753,15 +753,7 @@ the message being processed."
 			    (concat "^\\("
 				    (regexp-quote (user-login-name))
 				    "\\($\\|@\\)\\|"
-				    (regexp-quote
-				     ;; Don't lose if run from init file
-				     ;; where user-mail-address is not
-				     ;; set yet.
-				     (if (> (length user-mail-address) 0)
-					 user-mail-address
-				       (concat (user-login-name) "@"
-					       (or mail-host-address
-						   (system-name)))))
+				    (regexp-quote user-mail-address)
 				    "\\>\\)"))
 			from))
 		   ;; No From field, or it's this user.

lisp/startup.el

@@ -381,17 +381,14 @@ If this is nil, Emacs uses `system-name'."
   :type '(choice (const nil) string)
   :group 'mail)
 
-(defcustom user-mail-address (if command-line-processed
-				 (or (getenv "EMAIL")
-				     (concat (user-login-name) "@"
-					     (or mail-host-address
-						 (system-name))))
-			       ;; Empty string means "not set yet".
-			       "")
-  "Full mailing address of this user.
-This is initialized with environment variable `EMAIL' or, as a
-fallback, using `mail-host-address'.  This is done after your
-init file is read, in case it sets `mail-host-address'."
+(defcustom user-mail-address
+  (or (getenv "EMAIL")
+      (concat (user-login-name) "@" (or mail-host-address (system-name))))
+  "The email address of the current user.
+This defaults to either: the value of EMAIL environment variable; or
+user@host, using `user-login-name' and `mail-host-address' (or `system-name')."
+  :initialize 'custom-initialize-delay
+  :set-after '(mail-host-address)
   :type 'string
   :group 'mail)
 
@@ -1296,11 +1293,17 @@ the `--debug-init' option to view a complete error backtrace."
 	(set-language-environment current-language-environment)))
 
     ;; Do this here in case the init file sets mail-host-address.
-    (if (equal user-mail-address "")
-	(setq user-mail-address (or (getenv "EMAIL")
-				    (concat (user-login-name) "@"
-					    (or mail-host-address
-						(system-name))))))
+    (and mail-host-address
+	 ;; Check that user-mail-address has not been set by hand.
+	 ;; Yes, this is ugly, but slightly less so than leaving
+	 ;; user-mail-address uninitialized during init file processing.
+	 ;; Perhaps we should make :set-after do something like this?
+	 ;; Ie, extend it to also mean (re)initialize-after.
+	 (equal user-mail-address
+		(let (mail-host-address)
+		  (ignore-errors
+		    (eval (car (get 'user-mail-address 'standard-value))))))
+	 (custom-reevaluate-setting 'user-mail-address))
 
     ;; If parameter have been changed in the init file which influence
     ;; face realization, clear the face cache so that new faces will