[BUG] GetJsonObject removes leading space characters

[revans2]

Describe the bug
Spark and https://jsonpath.com/ agree that white space should not be stripped from the path. Our implementation treats $. a and $.a the same, but no other implementation I have found does that. What is more, even if the string is quoted we still end up doing the same thing $[' b'] is the same as $['b'].

[thirtiseven]

Ran some tests on current plugin with 3.4.1, gpu's results look the same as https://jsonpath.com/ 's, but not the same as cpu's, which treats $. a and $.a the same:

scala> val df = Seq("""{" a":"b","b":"c"}""", """{"a":"b","b":"c"}""", """{"a":"b"," a":"c"}""").toDF("value")
df: org.apache.spark.sql.DataFrame = [value: string]

scala> df.write.mode("overwrite").parquet("json_obj_data")

scala> val df2 = spark.read.parquet("json_obj_data")
df2: org.apache.spark.sql.DataFrame = [value: string]

scala> df2.selectExpr("value", "get_json_object(value, '$[\\\' a\\\']') as ba", "get_json_object(value, '$. a') as sa", "get_json_object(value, '$.a') as a").show()
+------------------+----+----+----+
|             value|  ba|  sa|   a|
+------------------+----+----+----+
|{" a":"b","b":"c"}|null|null|null|
|{"a":"b"," a":"c"}|   b|   b|   b|
| {"a":"b","b":"c"}|   b|   b|   b|
+------------------+----+----+----+


scala> spark.conf.set("spark.rapids.sql.enabled", true)

scala> spark.conf.set("spark.rapids.sql.expression.GetJsonObject", true)

scala> df2.selectExpr("value", "get_json_object(value, '$[\\\' a\\\']') as ba", "get_json_object(value, '$. a') as sa", "get_json_object(value, '$.a') as a").show()
24/02/22 14:50:49 WARN GpuOverrides:
!Exec <CollectLimitExec> cannot run on GPU because the Exec CollectLimitExec has been disabled, and is disabled by default because Collect Limit replacement can be slower on the GPU, if huge number of rows in a batch it could help by limiting the number of rows transferred from GPU to CPU. Set spark.rapids.sql.exec.CollectLimitExec to true if you wish to enable it
  @Partitioning <SinglePartition$> could run on GPU
  *Exec <ProjectExec> will run on GPU
    *Expression <Alias> get_json_object(value#94, $[' a']) AS ba#133 will run on GPU
      *Expression <GetJsonObject> get_json_object(value#94, $[' a']) will run on GPU
    *Expression <Alias> get_json_object(value#94, $. a) AS sa#134 will run on GPU
      *Expression <GetJsonObject> get_json_object(value#94, $. a) will run on GPU
    *Expression <Alias> get_json_object(value#94, $.a) AS a#135 will run on GPU
      *Expression <GetJsonObject> get_json_object(value#94, $.a) will run on GPU
    *Exec <FileSourceScanExec> will run on GPU

+------------------+----+----+----+
|             value|  ba|  sa|   a|
+------------------+----+----+----+
|{" a":"b","b":"c"}|   b|   b|null|
|{"a":"b"," a":"c"}|   c|   c|   b|
| {"a":"b","b":"c"}|null|null|   b|
+------------------+----+----+----+

Not sure if it's a bug of spark, we can match it in cudf as another get_json_object_options or do a pre-processing in plugin.