Fail fast and informatively for nonexistent file (r-lib#261)

* Initiate a snapshot test (non-informative failure)

* Fail early with a better message

* Explicitly check if `file` was provided

* Reveal the filepath that we can't find

* NEWS

Co-authored-by: Romain Francois <romain@rstudio.com>

Author: jennybc

NEWS.md

@@ -1,5 +1,7 @@
 # cpp11 (development version)
 
+* `cpp_source()` errors on non-existent file (#261). 
+
 # cpp11 0.4.2
 
 * Romain François is now the maintainer.

R/source.R

@@ -67,6 +67,9 @@
 #' @export
 cpp_source <- function(file, code = NULL, env = parent.frame(), clean = TRUE, quiet = TRUE, cxx_std = Sys.getenv("CXX_STD", "CXX11"), dir = tempfile()) {
   stop_unless_installed(c("brio", "callr", "cli", "decor", "desc", "glue", "tibble", "vctrs"))
+  if (!missing(file) && !file.exists(file)) {
+    stop("Can't find `file` at this path:\n", file, "\n", call. = FALSE)
+  }
 
   dir.create(dir, showWarnings = FALSE, recursive = TRUE)
   dir.create(file.path(dir, "R"), showWarnings = FALSE)

tests/testthat/_snaps/source.md

@@ -0,0 +1,8 @@
+# cpp_source fails informatively for nonexistent file
+
+    Code
+      cpp_source(i_do_not_exist)
+    Error <simpleError>
+      Can't find `file` at this path:
+      {NON_EXISTENT_FILEPATH}
+

tests/testthat/test-source.R

@@ -217,3 +217,13 @@ test_that("cpp_source(d) functions work after sourcing file more than once", {
   cpp11::cpp_source(test_path("single.cpp"), clean = TRUE)
   expect_equal(foo(), 1)
 })
+
+test_that("cpp_source fails informatively for nonexistent file", {
+  i_do_not_exist <- tempfile(pattern = "nope-", fileext = ".cpp")
+  expect_false(file.exists(i_do_not_exist))
+  expect_snapshot(
+    error = TRUE,
+    cpp_source(i_do_not_exist),
+    transform = ~ sub("^.+[.]cpp$", "{NON_EXISTENT_FILEPATH}", .x)
+  )
+})