Make require_testthat helper function (#2587)

* Make require_testthat helper function

* Update NEWS.md

* Add back testthat scopeing

* Roxygenise

* Add space in stop message

* Add a default to require_testthat

* avoid using linter_auto_name, add tests

* move NEWS entry

* I am in the wrong project. Notes is right indeed :)

* delint

* nolint false positive

---------

Co-authored-by: Michael Chirico <[email protected]>
Co-authored-by: Michael Chirico <[email protected]>

Author: F-Noelle

NEWS.md

@@ -10,6 +10,10 @@
    + Linters `closed_curly_linter()`, `open_curly_linter()`, `paren_brace_linter()`, and `semicolon_terminator_linter()`.
    + `linter=` argument of `Lint()`.
 
+## Notes
+
+* `expect_lint_free()` and other functions that rely on the {testthat} framework now have a consistent error message. (#2585, @F-Noelle).
+
 # lintr 3.2.0
 
 ## Deprecations & breaking changes

R/expect_lint.R

@@ -42,14 +42,8 @@
 #' )
 #' @export
 expect_lint <- function(content, checks, ..., file = NULL, language = "en") {
-  if (!requireNamespace("testthat", quietly = TRUE)) {
-    # nocov start
-    cli_abort(
-      # nolint next: line_length_linter.
-      "{.fun expect_lint} and {.fun expect_no_lint} are designed to work within the {.pkg testthat} testing framework, which is not installed."
-    )
-    # nocov end
-  }
+  require_testthat()
+
   old_lang <- set_lang(language)
   on.exit(reset_lang(old_lang))
 
@@ -123,6 +117,7 @@ expect_lint <- function(content, checks, ..., file = NULL, language = "en") {
 #' @rdname expect_lint
 #' @export
 expect_no_lint <- function(content, ..., file = NULL, language = "en") {
+  require_testthat()
   expect_lint(content, NULL, ..., file = file, language = language)
 }
 
@@ -135,6 +130,8 @@ expect_no_lint <- function(content, ..., file = NULL, language = "en") {
 #' @param ... arguments passed to [lint_package()]
 #' @export
 expect_lint_free <- function(...) {
+  require_testthat()
+
   testthat::skip_on_cran()
   testthat::skip_on_covr()
 
@@ -152,3 +149,16 @@ expect_lint_free <- function(...) {
 
   invisible(result)
 }
+
+# Helper function to check if testthat is installed.
+require_testthat <- function() {
+  parent_call <- sys.call(-1L)[[1L]]
+  # supported: foo() or lintr::foo(). Undefined behavior otherwise.
+  # nolint next: object_usage_linter. TODO(#2252): Remove this.
+  name <- as.character(if (is.name(parent_call)) parent_call else parent_call[[3L]])
+  if (!requireNamespace("testthat", quietly = TRUE)) {
+    cli_abort(
+      "{.fun {name}} is designed to work within the {.pkg testthat} testing framework, which could not be loaded."
+    )
+  }
+}

R/lintr-package.R

@@ -21,5 +21,8 @@ NULL
 
 # make binding available for mock testing
 # ref: https://testthat.r-lib.org/dev/reference/local_mocked_bindings.html#base-functions
+# nolint start: object_name_linter. These will be copied from base style.
+requireNamespace <- NULL
 unlink <- NULL
 quit <- NULL
+# nolint end: object_name_linter.

tests/testthat/test-expect_lint.R

@@ -70,3 +70,13 @@ test_that("expect_lint doesn't change language", {
     expect_identical(Sys.getenv("LANGUAGE"), "mr")
   })
 })
+
+test_that("execution without testthat gives the right errors", {
+  local_mocked_bindings(requireNamespace = function(...) FALSE)
+  lint_msg <- function(nm) rex::rex("`", nm, "()` is designed to work", anything, "testthat")
+
+  expect_error(expect_lint(), lint_msg("expect_lint"))
+  expect_error(lintr::expect_lint(), lint_msg("expect_lint"))
+  expect_error(expect_no_lint(), lint_msg("expect_no_lint"))
+  expect_error(expect_lint_free(), lint_msg("expect_lint_free"))
+})