[SPARK-22315][SPARKR] Warn if SparkR package version doesn't match Sp…

…arkContext

## What changes were proposed in this pull request?

This PR adds a check between the R package version used and the version reported by SparkContext running in the JVM. The goal here is to warn users when they have a R package downloaded from CRAN and are using that to connect to an existing Spark cluster.

This is raised as a warning rather than an error as users might want to use patch versions interchangeably (e.g., 2.1.3 with 2.1.2 etc.)

## How was this patch tested?

Manually by changing the `DESCRIPTION` file

Author: Shivaram Venkataraman <[email protected]>

Closes apache#19624 from shivaram/sparkr-version-check.

R/pkg/R/sparkR.R

@@ -420,6 +420,18 @@ sparkR.session <- function(
                                 enableHiveSupport)
     assign(".sparkRsession", sparkSession, envir = .sparkREnv)
   }
+
+  # Check if version number of SparkSession matches version number of SparkR package
+  jvmVersion <- callJMethod(sparkSession, "version")
+  # Remove -SNAPSHOT from jvm versions
+  jvmVersionStrip <- gsub("-SNAPSHOT", "", jvmVersion)
+  rPackageVersion <- paste0(packageVersion("SparkR"))
+
+  if (jvmVersionStrip != rPackageVersion) {
+    warning(paste("Version mismatch between Spark JVM and SparkR package. JVM version was",
+                  jvmVersion, ", while R package version was", rPackageVersion))
+  }
+
   sparkSession
 }