Fix #1282

.Rbuildignore

@@ -2,6 +2,7 @@
 ^build_site.R$
 ^pkgdown$
 ^\.DS_Store
+^_drake\.R$
 ^\.drake$
 ^\.drake_history$
 ^\.future$

.gitignore

@@ -18,6 +18,7 @@ Thumbs.db
 *.synctex.gz
 *.toc
 *.vrb
+_drake.R
 .drake
 .drake_history
 .DS_Store

NAMESPACE

@@ -104,6 +104,7 @@ export(drake_plan_source)
 export(drake_progress)
 export(drake_quotes)
 export(drake_running)
+export(drake_script)
 export(drake_session)
 export(drake_slice)
 export(drake_strings)

NEWS.md

@@ -11,6 +11,10 @@
 * Strongly depend on `tidyselect` (#1274, @dernst).
 * Avoid `txtq` lockfiles (#1232, #1239, #1280, @danwwilson, @pydupont, @mattwarkentin).
 
+## New features
+
+* Add a new `drake_script()` function to write `_drake.R` files for `r_make()` (#1282).
+
 # Version 7.12.2
 
 ## Bug fixes

R/drake_script.R

@@ -0,0 +1,45 @@
+#' @title Write an example `_drake.R` script to the current working directory.
+#' @export
+#' @description A `_drake.R` file is required for [r_make()] and friends.
+#'   See the [r_make()] help file for details.
+#' @return Nothing.
+#' @param code R code to put in `_drake.R` in the current working directory.
+#'   If `NULL`, an example script is written.
+#' @examples
+#' \dontrun{
+#' isolate_example("contain side-effects", {
+#' drake_script({
+#'   library(drake)
+#'   plan <- drake_plan(x = 1)
+#'   drake_config(plan, lock_cache = FALSE)
+#' })
+#' cat(readLines("_drake.R"), sep = "\n")
+#' r_make()
+#' })
+#' }
+drake_script <- function(code = NULL) {
+  code <- substitute(code)
+  if (length(code)) {
+    text <- parse_drake_script_code(code)
+  } else {
+    text <- example_drake_script()
+  }
+  writeLines(text, "_drake.R")
+}
+
+example_drake_script <- function() {
+  path <- system.file(
+    file.path("templates", "drake_script", "example_drake.R"),
+    package = "drake",
+    mustWork = TRUE
+  )
+  readLines(path)
+}
+
+parse_drake_script_code <- function(code) {
+  if (length(code) > 1L && safe_deparse(code[[1]]) == "`{`") {
+    vcapply(code[-1], safe_deparse)
+  } else {
+    safe_deparse(code)
+  }
+}

_pkgdown.yml

@@ -74,6 +74,7 @@ reference:
   - '`read_trace`'
 - title: Reproducible R session management
   contents:
+  - '`drake_script`'
   - '`r_make`'
   - '`r_drake_build`'
   - '`r_outdated`'

inst/templates/drake_script/example_drake.R

@@ -0,0 +1,39 @@
+# This file serves the r_*() functions (e.g. r_make()) documented at
+# https://books.ropensci.org/drake/projects.html#safer-interactivity # nolint
+# and
+# https://docs.ropensci.org/drake/reference/r_make.html
+
+# Load all your packages before calling make().
+library(drake)
+library(tibble)
+
+# Custom functions are an important part of a drake workflow.
+# This is where you write them.
+# Details: https://books.ropensci.org/drake/plans.html#functions
+
+generate_data <- function() {
+  tibble(x = rnorm(1e5), y = rnorm(1e5))
+}
+
+fit_model <- function(data) {
+  summary(lm(y ~ x, data = data))
+}
+
+# This is where you write your drake plan.
+# Details: https://books.ropensci.org/drake/plans.html
+
+plan <- drake_plan(
+  data = generate_data(),
+  model = fit_model(data)
+)
+
+# You could have put all the above into separate script files and
+# source()'d them as below:
+
+# source("R/packages.R")  # Load your packages, e.g. library(drake). # nolint
+# source("R/functions.R") # Define your custom code as a bunch of functions. # nolint
+# source("R/plan.R")      # Create your drake plan. # nolint
+
+# _drake.R must end with a call to drake_config().
+# The arguments to drake_config() are basically the same as those to make().
+drake_config(plan)

tests/testthat/test-zzz-callr.R

@@ -226,3 +226,21 @@ test_with_dir("errors keep their informative messages (#969)", {
     class = "callr_error"
   )
 })
+
+test_with_dir("drake_script() can generate an example script", {
+  drake_script()
+  expect_true(length(readLines("_drake.R")) > 0L)
+})
+
+test_with_dir("drake_script() can generate a single symbol", {
+  drake_script(x)
+  expect_equal(readLines("_drake.R"), "x")
+})
+
+test_with_dir("drake_script() can generate multiple lines", {
+  drake_script({
+    x
+    y
+  })
+  expect_equal(readLines("_drake.R"), c("x", "y"))
+})