Fix assertion error when describing mv as table

patch by Maciej Sokol; reviewed by Brandon Williams and Stefan Miklosovic for CASSANDRA-18596

CHANGES.txt

@@ -1,4 +1,5 @@
 4.0.11
+ * Fix assertion error when describing mv as table (CASSANDRA-18596)
  * Track the amount of read data per row (CASSANDRA-18513)
  * Fix Down nodes counter in nodetool describecluster (CASSANDRA-18512)
  * Remove unnecessary shuffling of GossipDigests in Gossiper#makeRandomGossipDigest (CASSANDRA-18546)

src/java/org/apache/cassandra/cql3/statements/DescribeStatement.java

@@ -472,7 +472,7 @@ public static DescribeStatement<SchemaElement> table(String keyspace, String nam
     {
         return new Element(keyspace, name, (ks, t) -> {
 
-            TableMetadata table = checkNotNull(ks.getTableOrViewNullable(t),
+            TableMetadata table = checkNotNull(ks.getTableNullable(t),
                                                "Table '%s' not found in keyspace '%s'", t, ks.name);
 
             return Stream.concat(Stream.of(table), table.indexes.stream()

src/java/org/apache/cassandra/schema/KeyspaceMetadata.java

@@ -153,6 +153,12 @@ public TableMetadata getTableOrViewNullable(String tableOrViewName)
              : view.metadata;
     }
 
+    @Nullable
+    public TableMetadata getTableNullable(String tableName)
+    {
+        return tables.getNullable(tableName);
+    }
+
     public boolean hasTable(String tableName)
     {
         return tables.get(tableName).isPresent();

test/unit/org/apache/cassandra/cql3/statements/DescribeStatementTest.java

@@ -598,6 +598,23 @@ public void testPrimaryKeyPositionWithAndWithoutInternals() throws Throwable
                           tableCreateStatementWithoutDroppedColumn));
     }
 
+    @Test
+    public void testDescribeMaterializedViewAsTable() throws Throwable
+    {
+        String table = createTable(KEYSPACE_PER_TEST, "CREATE TABLE IF NOT EXISTS %s (pk1 int, pk2 int, ck1 int, ck2 int, reg1 int, reg2 list<int>, reg3 int, PRIMARY KEY ((pk1, pk2), ck1, ck2)) WITH CLUSTERING ORDER BY (ck1 ASC, ck2 DESC);");
+
+        execute("CREATE MATERIALIZED VIEW IF NOT EXISTS " + KEYSPACE_PER_TEST + ".mv AS SELECT * FROM " + KEYSPACE_PER_TEST + '.' + table
+                + " WHERE pk2 IS NOT NULL AND pk1 IS NOT NULL AND ck2 IS NOT NULL AND ck1 IS NOT NULL PRIMARY KEY ((pk2, pk1), ck2, ck1)");
+        try
+        {
+            describeError(format("DESCRIBE TABLE %s.%s", KEYSPACE_PER_TEST, "mv"),
+                          format("Table '%s' not found in keyspace '%s'", "mv", KEYSPACE_PER_TEST));
+        }
+        finally
+        {
+            execute("DROP MATERIALIZED VIEW " + KEYSPACE_PER_TEST + ".mv");
+        }
+    }
 
     @Test
     public void testDescribeMissingKeyspace() throws Throwable