Throw an error for @importFrom unknown export

NEWS.md

@@ -1,5 +1,7 @@
 # roxygen2 (development version)
 
+* A friendlier error is thrown when attempting to import non-existing
+  functions with `@importFrom` (#1409, @MichaelChirico).
 * authors in `DESCRIPTION` can now have multiple email addresses (@jmbarbone, #1487).
 
 * The `ROXYGEN_PKG` environment variable is now set up while roxygen

R/namespace.R

@@ -238,6 +238,15 @@ roxy_tag_parse.roxy_tag_importFrom <- function(x) {
 }
 #' @export
 roxy_tag_ns.roxy_tag_importFrom <- function(x, block, env, import_only = FALSE) {
+  pkg <- x$val[1L]
+  if (requireNamespace(pkg, quietly = TRUE)) {
+    importing <- x$val[-1L]
+    unknown_idx <- !importing %in% getNamespaceExports(pkg)
+    if (any(unknown_idx)) {
+      warn_roxy_tag(x, "Excluding unknown {cli::qty(sum(unknown_idx))} export{?s} in from {.package {pkg}}: {.code {importing[unknown_idx]}}")
+      x$val <- c(pkg, importing[!unknown_idx])
+    }
+  }
   repeat_first_ignore_current("importFrom", x$val)
 }
 

tests/testthat/test-namespace.R

@@ -378,3 +378,38 @@ test_that("can extract non-imports from namespace preserving source", {
   path <- withr::local_tempfile(lines = lines)
   expect_equal(namespace_exports(path), lines[c(1:3, 5)])
 })
+
+test_that("Invalid imports throw a helpful error", {
+  expect_warning(
+    expect_equal(
+      roc_proc_text(namespace_roclet(), "
+        #' @importFrom utils head InvalidUtilsFunction
+        NULL
+      "),
+      "importFrom(utils,head)"
+    ),
+    "Excluding unknown export",
+    fixed = TRUE
+  )
+
+  # pluralization
+  expect_warning(
+    expect_equal(
+      roc_proc_text(namespace_roclet(), "
+        #' @importFrom utils head InvalidUtilsFunction1 InvalidUtilsFunction2
+        NULL
+      "),
+      "importFrom(utils,head)"
+    ),
+    "Excluding unknown exports"
+  )
+
+  # If the package is not available at roxygenize() run time, nothing we can do
+  expect_equal(
+    roc_proc_text(namespace_roclet(), "
+      #' @importFrom AnUnknownUnavailablePackage Unchecked
+      NULL
+    "),
+    "importFrom(AnUnknownUnavailablePackage,Unchecked)"
+  )
+})