bug#23590: 25.0.94; Errors in default lgrep command

[Juri Linkov]

>> The original bug report was about "M-x lgrep".  Can we make this
>> change affect only that command?
>>
>> In any case, this is a user-visible change, so it should be called out
>> in NEWS.
>
> Yup, and yup.

The latest fix has two problems:

1. it runs grep-probe every time lgrep is used;
2. it adds --directories=skip to the end of the command after regexp and file 
names

This patch improves both:

diff --git a/lisp/progmodes/grep.el b/lisp/progmodes/grep.el
index f028a4279d..9b1dc337e8 100644
--- a/lisp/progmodes/grep.el
+++ b/lisp/progmodes/grep.el
@@ -959,10 +959,10 @@ grep-expand-keywords
 these include `opts', `dir', `files', `null-device', `excl' and
 `regexp'.")
 
-(defun grep-expand-template (template &optional regexp files dir excl)
+(defun grep-expand-template (template &optional regexp files dir excl 
more-opts)
   "Expand grep COMMAND string replacing <C>, <D>, <F>, <R>, and <X>."
   (let* ((command template)
-         (env `((opts . ,(let (opts)
+         (env `((opts . ,(let ((opts more-opts))
                            (when (and case-fold-search
                                       (isearch-no-upper-case-p regexp t))
                              (push "-i" opts))
@@ -1058,6 +1058,8 @@ grep-read-files
         (or (cdr (assoc files grep-files-aliases))
             files))))
 
+(defvar grep-use-directories-skip 'auto-detect)
+
 ;;;###autoload
 (defun lgrep (regexp &optional files dir confirm)
   "Run grep, searching for REGEXP in FILES in directory DIR.
@@ -1103,6 +1105,12 @@ lgrep
          (if (string= command grep-command)
              (setq command nil))
        (setq dir (file-name-as-directory (expand-file-name dir)))
+       (unless (or (not grep-use-directories-skip) (eq 
grep-use-directories-skip t))
+         (setq grep-use-directories-skip
+               (grep-probe grep-program
+                         `(nil nil nil "--directories=skip" "foo"
+                               ,null-device)
+                         nil 1)))
        (setq command (grep-expand-template
                       grep-template
                       regexp
@@ -1119,13 +1127,10 @@ lgrep
                                                     (shell-quote-argument
                                                      (cdr ignore))))))
                                     grep-find-ignored-files
-                                    " --exclude=")))))
+                                    " --exclude=")))
+                      (and grep-use-directories-skip
+                           '("--directories=skip"))))
        (when command
-          (when (grep-probe grep-program
-                            `(nil nil nil "--directories=skip" "foo"
-                                  ,null-device)
-                            nil 1)
-            (setq command (concat command " --directories=skip")))
          (if confirm
              (setq command
                    (read-from-minibuffer "Confirm: "