XR: fix a crash on certain BGP/Address-family combinations (#5124)

* XR: fix a crash on certain BGP/Address-family combinations

projects/batfish/src/main/java/org/batfish/grammar/cisco/CiscoControlPlaneExtractor.java

@@ -7949,6 +7949,7 @@ public void exitNeighbor_block_address_family(Neighbor_block_address_familyConte
   public void exitNeighbor_block_rb_stanza(Neighbor_block_rb_stanzaContext ctx) {
     resetPeerGroups();
     if (_inBlockNeighbor) {
+      _inBlockNeighbor = false;
       popPeer();
     }
   }

projects/batfish/src/test/java/org/batfish/grammar/cisco/CiscoXrGrammarTest.java

@@ -0,0 +1,54 @@
+package org.batfish.grammar.cisco;
+
+import static org.hamcrest.Matchers.hasKey;
+import static org.junit.Assert.assertThat;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Map;
+import javax.annotation.Nonnull;
+import org.batfish.datamodel.Configuration;
+import org.batfish.main.BatfishTestUtils;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.junit.rules.TemporaryFolder;
+
+/** Tests for {@link CiscoParser} and {@link CiscoControlPlaneExtractor} on IOS-XR files. */
+public final class CiscoXrGrammarTest {
+
+  private static final String TESTCONFIGS_PREFIX = "org/batfish/grammar/cisco/testconfigs/";
+
+  @Rule public TemporaryFolder _folder = new TemporaryFolder();
+
+  @Rule public ExpectedException _thrown = ExpectedException.none();
+
+  private Map<String, Configuration> parseTextConfigs(String... configurationNames)
+      throws IOException {
+    String[] names =
+        Arrays.stream(configurationNames).map(s -> TESTCONFIGS_PREFIX + s).toArray(String[]::new);
+    return BatfishTestUtils.parseTextConfigs(_folder, names);
+  }
+
+  private @Nonnull Configuration parseConfig(String hostname) {
+    try {
+      Map<String, Configuration> configs = parseTextConfigs(hostname);
+      assertThat(configs, hasKey(hostname.toLowerCase()));
+      return configs.get(hostname.toLowerCase());
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  /**
+   * Regression test for a parser crash related to peer stack indexing issues.
+   *
+   * <p>The test config is a minimized version of user configuration submitted through Batfish
+   * diagnostics.
+   */
+  @Test
+  public void testXrBgpNeighbors() {
+    // Don't crash.
+    parseConfig("xr-bgp-neighbors");
+  }
+}

projects/batfish/src/test/resources/org/batfish/grammar/cisco/testconfigs/xr-bgp-neighbors

@@ -0,0 +1,17 @@
+!RANCID-CONTENT-TYPE: cisco-xr
+hostname xr-bgp-neighbors
+!
+router bgp 65000
+ !
+ ! BGP neighbor enabled for ipv4 unicast family
+ neighbor 1.2.3.4
+   address-family ipv4 unicast
+ !
+ ! Process-level config of router id
+ bgp router-id 1.2.3.5
+ ! Process-level config of address family
+ address-family ipv4 unicast
+ !
+ ! BGP neighbor enabled for ipv4 unicast family
+ neighbor 2.3.4.5
+   address-family ipv4 unicast