Description of the relationship between each module

This repo contains the code that integrate Hudi with Spark. The repo is split into the following modules

hudi-spark hudi-spark2 hudi-spark3 hudi-spark3.1.x hudi-spark2-common hudi-spark3-common hudi-spark-common

hudi-spark is the module that contains the code that both spark2 & spark3 version would share, also contains the antlr4 file that supports spark sql on spark 2.x version.
hudi-spark2 is the module that contains the code that compatible with spark 2.x versions.
hudi-spark3 is the module that contains the code that compatible with spark 3.2.0(and above) versions。
hudi-spark3.1.x is the module that contains the code that compatible with spark3.1.x and spark3.0.x version.
hudi-spark2-common is the module that contains the code that would be reused between spark2.x versions, right now the module has no class since hudi only supports spark 2.4.4 version, and it acts as the placeholder when packaging hudi-spark-bundle module.
hudi-spark3-common is the module that contains the code that would be reused between spark3.x versions.
hudi-spark-common is the module that contains the code that would be reused between spark2.x and spark3.x versions.

Description of Time Travel

HoodieSpark3_2ExtendedSqlAstBuilder have comments in the spark3.2's code fork from org.apache.spark.sql.catalyst.parser.AstBuilder, and additional withTimeTravel method.
SqlBase.g4 have comments in the code forked from spark3.2's parser, and add SparkSQL Syntax TIMESTAMP AS OF and VERSION AS OF.

Spark3.3 support time travel syntax link SPARK-37219. Once Spark 3.3 released. The files in the following list will be removed:

hudi-spark3's HoodieSpark3_2ExtendedSqlAstBuilder.scala、HoodieSpark3_2ExtendedSqlParser.scala、TimeTravelRelation.scala、SqlBase.g4、HoodieSqlBase.g4