[SPARK-51855] Support Spark SQL REPL

### What changes were proposed in this pull request?

This PR aims to support `Spark SQL REPL` via `Spark Connect for Swift` library.

### Why are the changes needed?

This is helpful for the users in two ways.
- Provide an interactive environment to use `Spark Connect for Swift` library for the production, development and testing.
- Provide a new simple and complete built-in example.

### Does this PR introduce _any_ user-facing change?

No, this is a new `executable` target of this project in addition to the existing `library` target.

### How was this patch tested?

Manual review by following new `README.md` content.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #77 from dongjoon-hyun/SPARK-51855.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

Package.swift

@@ -49,6 +49,10 @@ let package = Package(
         .product(name: "FlatBuffers", package: "flatbuffers"),
       ]
     ),
+    .executableTarget(
+      name: "SparkSQLRepl",
+      dependencies: ["SparkConnect"]
+    ),
     .testTarget(
       name: "SparkConnectTests",
       dependencies: ["SparkConnect"],

README.md

@@ -106,3 +106,73 @@ SELECT * FROM t
 
 You can find this example in the following repository.
 - https://github.com/dongjoon-hyun/spark-connect-swift-app
+
+## How to use `Spark SQL REPL` via `Spark Connect for Swift`
+
+This project also provides `Spark SQL REPL`. You can run it directly from this repository.
+
+```
+$ swift run
+...
+Build of product 'SQLRepl' complete! (2.33s)
+Connected to Apache Spark 4.0.0 Server
+spark-sql (default)> SHOW DATABASES;
++---------+
+|namespace|
++---------+
+|  default|
++---------+
+
+Time taken: 30 ms
+spark-sql (default)> CREATE DATABASE db1;
+++
+||
+++
+++
+
+Time taken: 31 ms
+spark-sql (default)> USE db1;
+++
+||
+++
+++
+
+Time taken: 27 ms
+spark-sql (db1)> CREATE TABLE t1 AS SELECT * FROM RANGE(10);
+++
+||
+++
+++
+
+Time taken: 99 ms
+spark-sql (db1)> SELECT * FROM t1;
++---+
+| id|
++---+
+|  1|
+|  5|
+|  3|
+|  0|
+|  6|
+|  9|
+|  4|
+|  8|
+|  7|
+|  2|
++---+
+
+Time taken: 80 ms
+spark-sql (db1)> USE default;
+++
+||
+++
+++
+
+Time taken: 26 ms
+spark-sql (default)> DROP DATABASE db1 CASCADE;
+++
+||
+++
+++
+spark-sql (default)> exit;
+```

Sources/SparkSQLRepl/main.swift

@@ -0,0 +1,52 @@
+//
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+//
+
+import Foundation
+import SparkConnect
+
+let statement = /([^;]*);/
+
+let spark = try await SparkSession.builder.getOrCreate()
+print("Connected to Apache Spark \(await spark.version) Server")
+
+var isRunning = true
+while isRunning {
+  print("spark-sql (\(try await spark.catalog.currentDatabase()))> ", terminator: "")
+  guard let input = readLine() else {
+    isRunning = false
+    break
+  }
+
+  let matches = input.matches(of: statement)
+  for match in matches {
+    switch match.1 {
+    case "exit":
+      isRunning = false
+      break
+    default:
+      do {
+        try await spark.time(spark.sql(String(match.1)).show)
+      } catch {
+        print("Error: \(error)")
+      }
+    }
+  }
+}
+
+await spark.stop()