grep: bug: backref in last of multiple patterns

* NEWS: Mention this.
* src/dfasearch.c (GEAcompile): Trim trailing newline from
the last pattern, even if it has back-references and follows
a pattern that lacks back-references.
* tests/backref: Add test for this bug.

NEWS

@@ -2,6 +2,12 @@ GNU grep NEWS                                    -*- outline -*-
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
+** Bug fixes
+
+  When given multiple patterns the last of which has a back-reference,
+  grep no longer sometimes mistakenly matches lines in some cases.
+  [Bug#36148#13 introduced in grep 3.4]
+
 
 * Noteworthy changes in release 3.8 (2022-09-02) [stable]
 

src/dfasearch.c

@@ -281,20 +281,19 @@ GEAcompile (char *pattern, idx_t size, reg_syntax_t syntax_bits,
   if (compilation_failed)
     exit (EXIT_TROUBLE);
 
-  if (prev <= patlim)
+  if (patlim < prev)
+    buflen--;
+  else if (pattern < prev)
     {
-      if (pattern < prev)
-        {
-          idx_t prevlen = patlim - prev;
-          buf = xirealloc (buf, buflen + prevlen);
-          memcpy (buf + buflen, prev, prevlen);
-          buflen += prevlen;
-        }
-      else
-        {
-          buf = pattern;
-          buflen = size;
-        }
+      idx_t prevlen = patlim - prev;
+      buf = xirealloc (buf, buflen + prevlen);
+      memcpy (buf + buflen, prev, prevlen);
+      buflen += prevlen;
+    }
+  else
+    {
+      buf = pattern;
+      buflen = size;
     }
 
   /* In the match_words and match_lines cases, we use a different pattern

tests/backref

@@ -43,4 +43,12 @@ if test $? -ne 2 ; then
         failures=1
 fi
 
+# https://bugs.gnu.org/36148#13
+echo 'Total failed: 2 (1 ignored)' |
+    grep -e '^Total failed: 0$' -e '^Total failed: \([0-9]*\) (\1 ignored)$'
+if test $? -ne 1 ; then
+        echo "Backref: Multiple -e test, test #5 failed"
+        failures=1
+fi
+
 Exit $failures