Sort Eshell aliases when adding new ones

The main point is to make the content of 'eshell-aliases-file' stable so
that storing it in git becomes feasible.

This also makes the output of the alias command come out in alphabetical
order (bug#80401).

* lisp/eshell/em-alias.el (eshell/alias): Sort when updating
'eshell-command-aliases-list'.

* test/lisp/eshell/em-alias-tests.el
(em-alias-test/alias-list-is-sorted): New test.

* etc/NEWS: Announce this change.

etc/NEWS

@@ -1977,6 +1977,13 @@ only search in input history.  If you customize it to the symbol 'dwim',
 those commands search in input history only when the point is after the
 last prompt.
 
+---
+*** Eshell 'alias' command now sorts the alias list.
+When adding an alias interactively, Eshell now sorts the list of aliases
+before saving the alias file.  This maintains the stability of the
+list of aliases to make the diff between versions more readable if you
+store your aliases in version control.
+
 ** Mail Utils
 
 +++

lisp/eshell/em-alias.el

@@ -173,7 +173,9 @@ file named by `eshell-aliases-file'.")
 	    (setq eshell-command-aliases-list
 		  (delq def eshell-command-aliases-list)))
 	(setq eshell-command-aliases-list
-	      (cons alias-def eshell-command-aliases-list))))
+	      (sort (cons alias-def eshell-command-aliases-list)
+                    (lambda (a b)
+                    (string< (car a) (car b)))))))
     (eshell-write-aliases-list))
   nil)
 

test/lisp/eshell/em-alias-tests.el

@@ -93,4 +93,13 @@
    (eshell-insert-command "alias add-funny-pair '+ $*[0][: 0] $*[1][: 1]'")
    (eshell-match-command-output "add-funny-pair 1:2 3:4" "5\n")))
 
+(ert-deftest em-alias-test/alias-list-is-sorted ()
+  "Test that the alias list is sorted on insert"
+  (with-temp-eshell
+   (eshell-insert-command "alias aaa 'aaa'")
+   (eshell-insert-command "alias ccc 'ccc'")
+   (eshell-insert-command "alias bbb 'bbb'")
+   (eshell-match-command-output
+    "alias" "alias aaa aaa\nalias bbb bbb\nalias ccc ccc\n")))
+
 ;; em-alias-tests.el ends here