[SPARK-19130][SPARKR] Support setting literal value as column implicitly

## What changes were proposed in this pull request?

```
df$foo <- 1
```

instead of
```
df$foo <- lit(1)
```

## How was this patch tested?

unit tests

Author: Felix Cheung <felixcheung_m@hotmail.com>

Closes apache#16510 from felixcheung/rlitcol.

Author: felixcheung

R/pkg/R/DataFrame.R

@@ -1727,14 +1727,21 @@ setMethod("$", signature(x = "SparkDataFrame"),
             getColumn(x, name)
           })
 
-#' @param value a Column or \code{NULL}. If \code{NULL}, the specified Column is dropped.
+#' @param value a Column or an atomic vector in the length of 1 as literal value, or \code{NULL}.
+#'              If \code{NULL}, the specified Column is dropped.
 #' @rdname select
 #' @name $<-
 #' @aliases $<-,SparkDataFrame-method
 #' @note $<- since 1.4.0
 setMethod("$<-", signature(x = "SparkDataFrame"),
           function(x, name, value) {
-            stopifnot(class(value) == "Column" || is.null(value))
+            if (class(value) != "Column" && !is.null(value)) {
+              if (isAtomicLengthOne(value)) {
+                value <- lit(value)
+              } else {
+                stop("value must be a Column, literal value as atomic in length of 1, or NULL")
+              }
+            }
 
             if (is.null(value)) {
               nx <- drop(x, name)
@@ -1947,10 +1954,10 @@ setMethod("selectExpr",
 #'
 #' @param x a SparkDataFrame.
 #' @param colName a column name.
-#' @param col a Column expression.
+#' @param col a Column expression, or an atomic vector in the length of 1 as literal value.
 #' @return A SparkDataFrame with the new column added or the existing column replaced.
 #' @family SparkDataFrame functions
-#' @aliases withColumn,SparkDataFrame,character,Column-method
+#' @aliases withColumn,SparkDataFrame,character-method
 #' @rdname withColumn
 #' @name withColumn
 #' @seealso \link{rename} \link{mutate}
@@ -1963,11 +1970,16 @@ setMethod("selectExpr",
 #' newDF <- withColumn(df, "newCol", df$col1 * 5)
 #' # Replace an existing column
 #' newDF2 <- withColumn(newDF, "newCol", newDF$col1)
+#' newDF3 <- withColumn(newDF, "newCol", 42)
 #' }
 #' @note withColumn since 1.4.0
 setMethod("withColumn",
-          signature(x = "SparkDataFrame", colName = "character", col = "Column"),
+          signature(x = "SparkDataFrame", colName = "character"),
           function(x, colName, col) {
+            if (class(col) != "Column") {
+              if (!isAtomicLengthOne(col)) stop("Literal value must be atomic in length of 1")
+              col <- lit(col)
+            }
             sdf <- callJMethod(x@sdf, "withColumn", colName, col@jc)
             dataFrame(sdf)
           })

R/pkg/R/utils.R

@@ -863,3 +863,7 @@ basenameSansExtFromUrl <- function(url) {
   # then, strip extension by the last '.'
   sub("([^.]+)\\.[[:alnum:]]+$", "\\1", filename)
 }
+
+isAtomicLengthOne <- function(x) {
+  is.atomic(x) && length(x) == 1
+}

R/pkg/inst/tests/testthat/test_sparkSQL.R

@@ -1001,6 +1001,17 @@ test_that("select operators", {
   expect_equal(columns(df), c("name", "age", "age2"))
   expect_equal(count(where(df, df$age2 == df$age * 2)), 2)
 
+  df$age2 <- 21
+  expect_equal(columns(df), c("name", "age", "age2"))
+  expect_equal(count(where(df, df$age2 == 21)), 3)
+
+  df$age2 <- c(22)
+  expect_equal(columns(df), c("name", "age", "age2"))
+  expect_equal(count(where(df, df$age2 == 22)), 3)
+
+  expect_error(df$age3 <- c(22, NA),
+              "value must be a Column, literal value as atomic in length of 1, or NULL")
+
   # Test parameter drop
   expect_equal(class(df[, 1]) == "SparkDataFrame", T)
   expect_equal(class(df[, 1, drop = T]) == "Column", T)
@@ -1778,6 +1789,13 @@ test_that("withColumn() and withColumnRenamed()", {
   expect_equal(length(columns(newDF)), 2)
   expect_equal(first(filter(newDF, df$name != "Michael"))$age, 32)
 
+  newDF <- withColumn(df, "age", 18)
+  expect_equal(length(columns(newDF)), 2)
+  expect_equal(first(newDF)$age, 18)
+
+  expect_error(withColumn(df, "age", list("a")),
+              "Literal value must be atomic in length of 1")
+
   newDF2 <- withColumnRenamed(df, "age", "newerAge")
   expect_equal(length(columns(newDF2)), 2)
   expect_equal(columns(newDF2)[1], "newerAge")