Fix failure when SHOW BRANCHES result is empty

Author: ebyhr

core/trino-main/src/main/java/io/trino/sql/rewrite/ShowQueriesRewrite.java

@@ -100,6 +100,7 @@
 import io.trino.sql.tree.TableElement;
 import io.trino.sql.tree.Values;
 
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
@@ -839,16 +840,21 @@ protected Node visitShowBranches(ShowBranches showBranches, Void context)
                 throw semanticException(TABLE_NOT_FOUND, showBranches, "Table '%s' does not exist", tableName);
             }
 
-            ImmutableList.Builder<Expression> rows = ImmutableList.builder();
+            String columnName = "Branch";
+            List<Expression> rows = new ArrayList<>();
             for (String branch : metadata.listBranches(session, tableName)) {
                 rows.add(row(new StringLiteral(branch)));
             }
 
+            if (rows.isEmpty()) {
+                return emptyQuery(ImmutableList.of(columnName), ImmutableList.of(VARCHAR));
+            }
+
             return simpleQuery(
                     selectList(
                             aliasedName("branch_name", "Branch")),
                     aliased(
-                            new Values(rows.build()),
+                            new Values(ImmutableList.copyOf(rows)),
                             "branches",
                             ImmutableList.of("branch_name")));
         }

core/trino-main/src/test/java/io/trino/sql/query/TestShowQueries.java

@@ -317,6 +317,12 @@ public void testShowCreateViewWithProperties()
                           mock_table""");
     }
 
+    @Test
+    void testShowBranchesEmptyResult()
+    {
+        assertions.assertQueryReturnsEmptyResult("SHOW BRANCHES FROM TABLE mock.mockSchema.mockTable");
+    }
+
     private static ColumnMetadata columnMetadata(String name, Type type, String value)
     {
         return ColumnMetadata.builder().setName(name).setType(type).setDefaultValue(Optional.of(value)).build();