Address comments.

Author: viirya

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala

@@ -1409,7 +1409,7 @@ class AstBuilder(conf: SQLConf) extends SqlBaseBaseVisitor[AnyRef] with Logging
    * Special characters can be escaped by using Hive/C-style escaping.
    */
   private def createString(ctx: StringLiteralContext): String = {
-    if (conf.noUnescapedStringLiteral) {
+    if (conf.escapedStringLiterals) {
       ctx.STRING().asScala.map(stringWithoutUnescape).mkString
     } else {
       ctx.STRING().asScala.map(string).mkString

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/ParserUtils.scala

@@ -70,6 +70,7 @@ object ParserUtils {
 
   /** Convert a string node into a string without unescaping. */
   def stringWithoutUnescape(node: TerminalNode): String = {
+    // STRING parser rule forces that the input always has quotes at the starting and ending.
     node.getText.slice(1, node.getText.size - 1)
   }
 

sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala

@@ -196,11 +196,11 @@ object SQLConf {
     .booleanConf
     .createWithDefault(true)
 
-  val NO_UNESCAPED_SQL_STRING = buildConf("spark.sql.noUnescapedStringLiteral")
+  val ESCAPED_STRING_LITERALS = buildConf("spark.sql.parser.escapedStringLiterals")
     .internal()
-    .doc("Since Spark 2.0, we use unescaped SQL string for string literals including regex. " +
-      "It is different than 1.6 behavior. Enabling this config can use no unescaped SQL string " +
-      "literals and mitigate migration problem.")
+    .doc("When true, string literals (including regex patterns) remains escaped in our SQL " +
+      "parser. The default is false since Spark 2.0. Setting it to true can restore the behavior " +
+      "prior to Spark 2.0.")
     .booleanConf
     .createWithDefault(false)
 
@@ -919,7 +919,7 @@ class SQLConf extends Serializable with Logging {
 
   def constraintPropagationEnabled: Boolean = getConf(CONSTRAINT_PROPAGATION_ENABLED)
 
-  def noUnescapedStringLiteral: Boolean = getConf(NO_UNESCAPED_SQL_STRING)
+  def escapedStringLiterals: Boolean = getConf(ESCAPED_STRING_LITERALS)
 
   /**
    * Returns the [[Resolver]] for the current configuration, which can be used to determine if two

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/parser/ExpressionParserSuite.scala

@@ -166,9 +166,9 @@ class ExpressionParserSuite extends PlanTest {
     assertEqual("a not regexp 'pattern%'", !('a rlike "pattern%"))
   }
 
-  test("like expressions with NO_UNESCAPED_SQL_STRING") {
+  test("like expressions with ESCAPED_STRING_LITERALS = true") {
     val conf = new SQLConf()
-    conf.setConfString("spark.sql.noUnescapedStringLiteral", "true")
+    conf.setConfString("spark.sql.parser.escapedStringLiterals", "true")
     val parser = new CatalystSqlParser(conf)
     assertEqual("a rlike '^\\x20[\\x20-\\x23]+$'", 'a rlike "^\\x20[\\x20-\\x23]+$", parser)
     assertEqual("a rlike 'pattern\\\\'", 'a rlike "pattern\\\\", parser)
@@ -462,9 +462,9 @@ class ExpressionParserSuite extends PlanTest {
     assertEqual("'\\u0057\\u006F\\u0072\\u006C\\u0064\\u0020\\u003A\\u0029'", "World :)")
   }
 
-  test("strings with NO_UNESCAPED_SQL_STRING") {
+  test("strings with ESCAPED_STRING_LITERALS = true") {
     val conf = new SQLConf()
-    conf.setConfString("spark.sql.noUnescapedStringLiteral", "true")
+    conf.setConfString("spark.sql.parser.escapedStringLiterals", "true")
     val parser = new CatalystSqlParser(conf)
 
     // Single Strings.

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

@@ -1171,7 +1171,7 @@ class DatasetSuite extends QueryTest with SharedSQLContext {
   }
 
   test("do not unescaped regex pattern string") {
-    withSQLConf(SQLConf.NO_UNESCAPED_SQL_STRING.key -> "true") {
+    withSQLConf(SQLConf.ESCAPED_STRING_LITERALS.key -> "true") {
       val data = Seq("\u0020\u0021\u0023", "abc")
       val df = data.toDF()
       val rlike1 = df.filter("value rlike '^\\x20[\\x20-\\x23]+$'")