From 7e826ea733f734f5df13ee4a895017f4c74f60cc Mon Sep 17 00:00:00 2001
From: Brian Connelly <bconnelly@ookla.com>
Date: Mon, 28 Aug 2023 14:26:09 -0700
Subject: [PATCH] Add `using_nix_shell()`

---
 NAMESPACE                 |  1 +
 NEWS.md                   |  2 ++
 R/nix.R                   | 36 ++++++++++++++++++++++++++++++++++++
 _pkgdown.yml              |  1 +
 man/nix.Rd                | 26 ++++++++++++++++++++++++++
 tests/testthat/test-nix.R | 27 +++++++++++++++++++++++++++
 6 files changed, 93 insertions(+)
 create mode 100644 R/nix.R
 create mode 100644 man/nix.Rd
 create mode 100644 tests/testthat/test-nix.R

diff --git a/NAMESPACE b/NAMESPACE
index 36e410f..47ecb70 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -25,6 +25,7 @@ export(using_kubernetes)
 export(using_latest_r_version)
 export(using_linux)
 export(using_macos)
+export(using_nix_shell)
 export(using_option)
 export(using_os)
 export(using_podman_container)
diff --git a/NEWS.md b/NEWS.md
index 0be4f43..32f7c49 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,7 @@
 # ami 0.1.0.9000
 
+* Added `using_nix_shell()` for detecting [Nix shell environments](https://nixos.org/manual/nix/unstable/command-ref/nix-shell.html)
+
 # ami 0.1.0
 
 * Initial public release
diff --git a/R/nix.R b/R/nix.R
new file mode 100644
index 0000000..5d497c4
--- /dev/null
+++ b/R/nix.R
@@ -0,0 +1,36 @@
+#' @rdname nix
+#' @title Detect `Nix` Shell
+#'
+#' @description `using_nix_shell()` checks whether code is running within an
+# nolint start
+#' environment defined by a [Nix expression](https://nixos.org/manual/nix/unstable/command-ref/nix-shell.html).
+# nolint end
+#'
+#' @param pure Whether or not the environment is pure, meaning most environment
+#'   variables have been cleared before the shell started.
+#'
+#' @return A logical value
+#' @export
+#'
+#' @examples
+#' # Check for Nix
+#' using_nix_shell()
+#'
+#' # Check for Nix in a pure environment
+#' using_nix_shell(pure = TRUE)
+using_nix_shell <- function(pure = NULL) {
+  if (!rlang::is_logical(pure, n = 1) && !rlang::is_null(pure)) {
+    rlang::abort(
+      message = "`pure` should be a logical scalar",
+      class = "arg_not_scalar_logical"
+    )
+  }
+
+  if (isTRUE(pure)) {
+    using_envvar("IN_NIX_SHELL", "pure")
+  } else if (isFALSE(pure)) {
+    using_envvar("IN_NIX_SHELL", "impure")
+  } else {
+    using_envvar("IN_NIX_SHELL")
+  }
+}
diff --git a/_pkgdown.yml b/_pkgdown.yml
index fc69e6f..d229013 100644
--- a/_pkgdown.yml
+++ b/_pkgdown.yml
@@ -73,4 +73,5 @@ reference:
     desc: Additional checks
     contents:
     - using_databricks
+    - using_nix_shell
 
diff --git a/man/nix.Rd b/man/nix.Rd
new file mode 100644
index 0000000..edf1294
--- /dev/null
+++ b/man/nix.Rd
@@ -0,0 +1,26 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/nix.R
+\name{using_nix_shell}
+\alias{using_nix_shell}
+\title{Detect \code{Nix} Shell}
+\usage{
+using_nix_shell(pure = NULL)
+}
+\arguments{
+\item{pure}{Whether or not the environment is pure, meaning most environment
+variables have been cleared before the shell started.}
+}
+\value{
+A logical value
+}
+\description{
+\code{using_nix_shell()} checks whether code is running within an
+environment defined by a \href{https://nixos.org/manual/nix/unstable/command-ref/nix-shell.html}{Nix expression}.
+}
+\examples{
+# Check for Nix
+using_nix_shell()
+
+# Check for Nix in a pure environment
+using_nix_shell(pure = TRUE)
+}
diff --git a/tests/testthat/test-nix.R b/tests/testthat/test-nix.R
new file mode 100644
index 0000000..f42cd36
--- /dev/null
+++ b/tests/testthat/test-nix.R
@@ -0,0 +1,27 @@
+test_that("using_nix_shell validates input properly", {
+  expect_error(using_nix_shell(pure = NA_character_))
+  expect_error(using_nix_shell(pure = 1))
+  expect_error(using_nux_shell(pure = "pure"))
+  expect_error(using_nix_shell(pure = c(TRUE, TRUE)))
+})
+
+test_that("using_nix_shell works as expected when `IN_NIX_SHELL` not set", {
+  withr::local_envvar(list("IN_NIX_SHELL" = NA))
+  expect_false(using_nix_shell())
+  expect_false(using_nix_shell(pure = TRUE))
+  expect_false(using_nix_shell(pure = FALSE))
+})
+
+test_that("using_nix_shell works as expected in pure environment", {
+  withr::local_envvar(list("IN_NIX_SHELL" = "pure"))
+  expect_true(using_nix_shell())
+  expect_true(using_nix_shell(pure = TRUE))
+  expect_false(using_nix_shell(pure = FALSE))
+})
+
+test_that("using_nix_shell works as expected in impure environment", {
+  withr::local_envvar(list("IN_NIX_SHELL" = "impure"))
+  expect_true(using_nix_shell())
+  expect_false(using_nix_shell(pure = TRUE))
+  expect_true(using_nix_shell(pure = FALSE))
+})