mu4e: better feedback for lazy indexing

Add `mu4e-update-index-nonlazy`, point users towards it.

mu4e/mu4e-utils.el

@@ -644,8 +644,13 @@ process."
            "Indexing... processed %d, updated %d" processed updated)
         (progn
           (mu4e-index-message
-           "Indexing completed; processed %d, updated %d, cleaned-up %d"
-           processed updated cleaned-up)
+           "%s completed; processed %d, updated %d, cleaned-up %d%s"
+           (if mu4e-index-lazy-check "Lazy indexing" "Indexing")
+           processed updated cleaned-up
+           (if (and mu4e-index-lazy-check
+                    (not (eq mu4e-index-lazy-check 'lazy))
+                    (= 0 updated))
+               " (consider M-x mu4e-update-nonlazy)" ""))
           ;; call the updated hook if anything changed.
           (unless (zerop (+ updated cleaned-up))
             (run-hooks 'mu4e-index-updated-hook))
@@ -945,7 +950,17 @@ Also scrolls to the final line, and update the progress throbber."
 (defun mu4e-update-index ()
   "Update the mu4e index."
   (interactive)
-  (mu4e~proc-index  mu4e-index-cleanup mu4e-index-lazy-check))
+  (mu4e~proc-index mu4e-index-cleanup mu4e-index-lazy-check))
+
+(defun mu4e-update-index-nonlazy ()
+  "Update the mu4e index non-lazily.
+This is just a convenience wrapper for indexing the non-lazy way
+if you otherwise want to use `mu4e-index-lazy-check'."
+  (interactive)
+  (let ((mu4e-index-cleanup nil) (mu4e-index-lazy-check nil))
+    (mu4e-update-index)))
+
+
 
 (defvar mu4e~update-buffer nil
   "Internal, store the buffer of the update process when

mu4e/mu4e-vars.el

@@ -138,7 +138,12 @@ limitations: since directory timestamp changes do not traverse
 upwards and therefore this does not see changes in
 sub-directories: a change in 'bar' in 'Maildir/foo/bar/...' is
 not detected, only a change in 'foo'. In that case, this option
-should not be set."
+should not be set.
+
+Note: if no updated/new message were found during the lazy check,
+mu4e will suggest using `mu4e-update-index-nonlazy'; if you do
+not wish to see that suggestion, set `mu4e-index-lazy-check' to the
+symbol `lazy'."
   :type 'boolean
   :group 'mu4e
   :safe 'booleanp)

mu4e/mu4e.texi

@@ -611,8 +611,12 @@ following:
 @end lisp
 
 In many cases, the mentioned thoroughness might not be needed, and
-these settings give a very significant speed-up. Note that you can of
-course occasionally run a thorough indexing round.
+these settings give a very significant speed-up. If it does not work
+for you (e.g., @t{mu4e} fails to find some new messages), simply leave
+at the default.
+
+Note that you can occasionally run a thorough indexing round using
+@code{mu4e-update-index-nonlazy}.
 
 For further details, please refer to the @t{mu-index} manpage; in
 particular, see @t{.noindex} and @t{.noupdate} which can help reducing