patch 8.0.0645: no error for illegal back reference in NFA enginev8.0.0645

Problem:    The new regexp engine does not give an error for using a back
            reference where it is not allowed. (Dominique Pelle)
Solution:   Check the back reference like the old engine. (closes #1774)

1 files changed, 30 insertions, 18 deletions

diff --git a/src/regexp.c b/src/regexp.c
index 74a73c440..7304bd349 100644
--- a/src/regexp.c
+++ b/src/regexp.c
@@ -1294,6 +1294,34 @@ skip_regexp(
     return p;
 }
 
+/*
+ * Return TRUE if the back reference is legal. We must have seen the close
+ * brace.
+ * TODO: Should also check that we don't refer to something that is repeated
+ * (+*=): what instance of the repetition should we match?
+ */
+    static int
+seen_endbrace(int refnum)
+{
+    if (!had_endbrace[refnum])
+    {
+	char_u *p;
+
+	/* Trick: check if "@<=" or "@<!" follows, in which case
+	 * the \1 can appear before the referenced match. */
+	for (p = regparse; *p != NUL; ++p)
+	    if (p[0] == '@' && p[1] == '<' && (p[2] == '!' || p[2] == '='))
+		break;
+	if (*p == NUL)
+	{
+	    EMSG(_("E65: Illegal back reference"));
+	    rc_did_emsg = TRUE;
+	    return FALSE;
+	}
+    }
+    return TRUE;
+}
+
 static regprog_T  *bt_regcomp(char_u *expr, int re_flags);
 static void bt_regfree(regprog_T *prog);
 
@@ -2099,24 +2127,8 @@ regatom(int *flagp)
 		int		    refnum;
 
 		refnum = c - Magic('0');
-		/*
-		 * Check if the back reference is legal. We must have seen the
-		 * close brace.
-		 * TODO: Should also check that we don't refer to something
-		 * that is repeated (+*=): what instance of the repetition
-		 * should we match?
-		 */
-		if (!had_endbrace[refnum])
-		{
-		    /* Trick: check if "@<=" or "@<!" follows, in which case
-		     * the \1 can appear before the referenced match. */
-		    for (p = regparse; *p != NUL; ++p)
-			if (p[0] == '@' && p[1] == '<'
-					      && (p[2] == '!' || p[2] == '='))
-			    break;
-		    if (*p == NUL)
-			EMSG_RET_NULL(_("E65: Illegal back reference"));
-		}
+		if (!seen_endbrace(refnum))
+		    return NULL;
 		ret = regnode(BACKREF + refnum);
 	    }
 	    break;