updated for version 7.3.850

Problem:    ":vimgrep //" matches everywhere.
Solution:   Make it use the previous search pattern. (David Bürgin)

runtime/doc/quickfix.txt

@@ -574,6 +574,8 @@ commands can be combined to create a NewGrep command: >
 			'ignorecase' applies.  To overrule it put |/\c| in the
 			pattern to ignore case or |/\C| to match case.
 			'smartcase' is not used.
+			If {pattern} is empty (e.g. // is specified), the last
+			used search pattern is used. |last-pattern|
 
 			When a number is put before the command this is used
 			as the maximum number of matches to find.  Use

src/quickfix.c

@@ -3179,7 +3179,20 @@ ex_vimgrep(eap)
 	EMSG(_(e_invalpat));
 	goto theend;
     }
-    regmatch.regprog = vim_regcomp(s, RE_MAGIC);
+
+    if (s != NULL && *s == NUL)
+    {
+	/* Pattern is empty, use last search pattern. */
+	if (last_search_pat() == NULL)
+	{
+	    EMSG(_(e_noprevre));
+	    goto theend;
+	}
+	regmatch.regprog = vim_regcomp(last_search_pat(), RE_MAGIC);
+    }
+    else
+	regmatch.regprog = vim_regcomp(s, RE_MAGIC);
+
     if (regmatch.regprog == NULL)
 	goto theend;
     regmatch.rmm_ic = p_ic;

src/version.c

@@ -728,6 +728,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    850,
 /**/
     849,
 /**/