[SPARK-33690][SQL] Escape meta-characters in showString

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

This PR intends to escape meta-characters (e.g., \n and \t) in `Dataset.showString`.
Before this PR:
```
scala> Seq("aaa\nbbb\t\tccccc").toDF("value").show()
+--------------+
|         value|
+--------------+
|aaa
bbb		ccccc|
+--------------+
```
After this PR:
```
+-----------------+
|            value|
+-----------------+
|aaa\nbbb\t\tccccc|
+-----------------+
```

### Why are the changes needed?

For better output.

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

No.

### How was this patch tested?

Added a unit test.

Closes apache#30647 from maropu/EscapeMetaInShow.

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

Author: maropu

docs/sql-migration-guide.md

@@ -26,6 +26,8 @@ license: |
 
   - In Spark 3.2, `spark.sql.adaptive.enabled` is enabled by default. To restore the behavior before Spark 3.2, you can set `spark.sql.adaptive.enabled` to `false`.
 
+  - In Spark 3.2, the meta-characters `\n` and `\t` are escaped in the `show()` action. In Spark 3.1 or earlier, the two metacharacters are output as it is.
+
 ## Upgrading from Spark SQL 3.0 to 3.1
 
   - In Spark 3.1, statistical aggregation function includes `std`, `stddev`, `stddev_samp`, `variance`, `var_samp`, `skewness`, `kurtosis`, `covar_samp`, `corr` will return `NULL` instead of `Double.NaN` when `DivideByZero` occurs during expression evaluation, for example, when `stddev_samp` applied on a single element set. In Spark version 3.0 and earlier, it will return `Double.NaN` in such case. To restore the behavior before Spark 3.1, you can set `spark.sql.legacy.statisticalAggregate` to `true`.

sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala

@@ -308,7 +308,9 @@ class Dataset[T] private[sql](
         val str = cell match {
           case null => "null"
           case binary: Array[Byte] => binary.map("%02X".format(_)).mkString("[", " ", "]")
-          case _ => cell.toString
+          case _ =>
+            // Escapes meta-characters not to break the `showString` format
+            cell.toString.replaceAll("\n", "\\\\n").replaceAll("\t", "\\\\t")
         }
         if (truncate > 0 && str.length > truncate) {
           // do not show ellipses for strings shorter than 4 characters.

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

@@ -1235,6 +1235,44 @@ class DataFrameSuite extends QueryTest
     assert(df.showString(10, vertical = true) === expectedAnswer)
   }
 
+  test("SPARK-33690: showString: escape meta-characters") {
+    val df1 = Seq("aaa\nbbb\tccc").toDF("value")
+    assert(df1.showString(1, truncate = 0) ===
+      """+-------------+
+        ||value        |
+        |+-------------+
+        ||aaa\nbbb\tccc|
+        |+-------------+
+        |""".stripMargin)
+
+    val df2 = Seq(Seq("aaa\nbbb\tccc")).toDF("value")
+    assert(df2.showString(1, truncate = 0) ===
+      """+---------------+
+        ||value          |
+        |+---------------+
+        ||[aaa\nbbb\tccc]|
+        |+---------------+
+        |""".stripMargin)
+
+    val df3 = Seq(Map("aaa\nbbb\tccc" -> "aaa\nbbb\tccc")).toDF("value")
+    assert(df3.showString(1, truncate = 0) ===
+      """+--------------------------------+
+        ||value                           |
+        |+--------------------------------+
+        ||{aaa\nbbb\tccc -> aaa\nbbb\tccc}|
+        |+--------------------------------+
+        |""".stripMargin)
+
+    val df4 = Seq("aaa\nbbb\tccc").toDF("value").selectExpr("named_struct('v', value)")
+    assert(df4.showString(1, truncate = 0) ===
+      """+----------------------+
+        ||named_struct(v, value)|
+        |+----------------------+
+        ||{aaa\nbbb\tccc}       |
+        |+----------------------+
+        |""".stripMargin)
+  }
+
   test("SPARK-7319 showString") {
     val expectedAnswer = """+---+-----+
                            ||key|value|

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

@@ -261,11 +261,11 @@ class ExplainSuite extends ExplainSuiteHelper with DisableAdaptiveExecutionSuite
             "PartitionFilters: \\[isnotnull\\(k#xL\\), dynamicpruningexpression\\(k#xL " +
               "IN subquery#x\\)\\]"
           val expected_pattern3 =
-            "Location: InMemoryFileIndex \\[.*org.apache.spark.sql.ExplainSuite" +
-              "/df2/.*, ... 99 entries\\]"
+            "Location: InMemoryFileIndex \\[\\S*org.apache.spark.sql.ExplainSuite" +
+              "/df2/\\S*, ... 99 entries\\]"
           val expected_pattern4 =
-            "Location: InMemoryFileIndex \\[.*org.apache.spark.sql.ExplainSuite" +
-              "/df1/.*, ... 999 entries\\]"
+            "Location: InMemoryFileIndex \\[\\S*org.apache.spark.sql.ExplainSuite" +
+              "/df1/\\S*, ... 999 entries\\]"
           withNormalizedExplain(sqlText) { normalizedOutput =>
             assert(expected_pattern1.r.findAllMatchIn(normalizedOutput).length == 1)
             assert(expected_pattern2.r.findAllMatchIn(normalizedOutput).length == 1)