[SPARK-57128][SQL][TESTS] SQLQueryTestHelper --SET parser must preserve commas in config values

What changes were proposed in this pull request?

`SQLQueryTestHelper.getSparkSettings` splits `--SET` directive values on every
comma, which conflicts with Spark configs whose values themselves contain commas
(e.g. `spark.sql.optimizer.excludedRules` accepts a comma-separated rule list).
The current parser crashes with `StringIndexOutOfBoundsException` when it
encounters such a value.

Change the split to only occur at commas that are immediately followed by what
looks like a new `key=` (word characters or dots ending in `=`). This preserves
the documented multi-setting form `--SET k1=v1,k2=v2` while allowing values to
contain commas.

Adds `SQLQueryTestHelperSuite` with focused unit tests.

Why are the changes needed?

The parser cannot currently express settings whose values contain commas,
forcing users to scope down their SET to a single value. This was hit when
trying to specify a multi-rule `excludedRules` value in Apache Gluten's spark41
SQL test workaround (apache/gluten#12165).

Does this PR introduce any user-facing change?

No. Test-framework-only change. Existing tests that rely on the documented
multi-setting form continue to parse as before.

How was this patch tested?

New `SQLQueryTestHelperSuite` with 6 cases covering: single setting, multi-
setting in one `--SET`, multiple `--SET` lines, comma-containing value,
mixed, and non-SET comments. All pass.

Author: rdtr

sql/core/src/test/scala/org/apache/spark/sql/SQLQueryTestHelper.scala

@@ -474,7 +474,12 @@ trait SQLQueryTestHelper extends SQLConfHelper with Logging {
 
   protected def getSparkSettings(comments: Array[String]): Array[(String, String)] = {
     val settingLines = comments.filter(_.startsWith("--SET ")).map(_.substring(6))
-    settingLines.flatMap(_.split(",").map { kv =>
+    // Split on commas that are followed by what looks like a new `key=`. This preserves
+    // commas inside config values such as
+    //   --SET spark.sql.optimizer.excludedRules=Rule1,Rule2
+    // while still supporting the documented multi-setting form
+    //   --SET key1=v1,key2=v2
+    settingLines.flatMap(_.split(",(?=[\\w.]+=)").map { kv =>
       val (conf, value) = kv.span(_ != '=')
       conf.trim -> value.substring(1).trim
     })

sql/core/src/test/scala/org/apache/spark/sql/SQLQueryTestHelperSuite.scala

@@ -0,0 +1,64 @@
+/*
+ * 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.
+ */
+package org.apache.spark.sql
+
+import org.apache.spark.SparkFunSuite
+
+class SQLQueryTestHelperSuite extends SparkFunSuite with SQLQueryTestHelper {
+
+  test("getSparkSettings: single key=value") {
+    val result = getSparkSettings(Array("--SET spark.sql.foo=1"))
+    assert(result.toSeq === Seq("spark.sql.foo" -> "1"))
+  }
+
+  test("getSparkSettings: multiple key=value pairs in one --SET (documented form)") {
+    val result = getSparkSettings(Array("--SET spark.sql.foo=1,spark.sql.bar=2"))
+    assert(result.toSeq === Seq("spark.sql.foo" -> "1", "spark.sql.bar" -> "2"))
+  }
+
+  test("getSparkSettings: multiple --SET statements") {
+    val result = getSparkSettings(
+      Array("--SET spark.sql.foo=1", "--SET spark.sql.bar=2"))
+    assert(result.toSeq === Seq("spark.sql.foo" -> "1", "spark.sql.bar" -> "2"))
+  }
+
+  test("getSparkSettings: value containing commas (e.g. excludedRules list)") {
+    val excludedRules =
+      "org.apache.spark.sql.catalyst.optimizer.ConvertToLocalRelation," +
+        "org.apache.spark.sql.catalyst.optimizer.ConstantFolding"
+    val result = getSparkSettings(
+      Array(s"--SET spark.sql.optimizer.excludedRules=$excludedRules"))
+    assert(result.toSeq === Seq("spark.sql.optimizer.excludedRules" -> excludedRules))
+  }
+
+  test("getSparkSettings: mixed -- multiple settings where one value contains commas") {
+    val excludedRules =
+      "org.apache.spark.sql.catalyst.optimizer.ConvertToLocalRelation," +
+        "org.apache.spark.sql.catalyst.optimizer.ConstantFolding"
+    val result = getSparkSettings(
+      Array(s"--SET spark.sql.optimizer.excludedRules=$excludedRules,spark.sql.foo=1"))
+    assert(result.toSeq === Seq(
+      "spark.sql.optimizer.excludedRules" -> excludedRules,
+      "spark.sql.foo" -> "1"))
+  }
+
+  test("getSparkSettings: ignores non --SET comments") {
+    val result = getSparkSettings(
+      Array("-- a comment", "--SET spark.sql.foo=1", "-- another"))
+    assert(result.toSeq === Seq("spark.sql.foo" -> "1"))
+  }
+}