Add ExUnit.TmpDir.tmp_dir/0

Inspired by golang/go#35998.

lib/ex_unit/lib/ex_unit/case.ex

@@ -513,6 +513,8 @@ defmodule ExUnit.Case do
 
  test = %ExUnit.Test{name: name, case: mod, tags: tags, module: mod}
  Module.put_attribute(mod, :ex_unit_tests, test)
+ Module.put_attribute(mod, :ex_unit_test, test)
+ Module.put_attribute(mod, :ex_unit_tmp_dirs, [])
 
  for attribute <- Module.get_attribute(mod, :ex_unit_registered_test_attributes) do
  Module.delete_attribute(mod, attribute)

lib/ex_unit/lib/ex_unit/tmp_dir.ex

@@ -0,0 +1,33 @@
+defmodule ExUnit.TmpDir do
+ @doc """
+ Returns a path to a temporary directory for the current test.
+
+ The directory is lazily created on the first access and is automatically
+ removed once the test finishes (regardless if the test suceeds or fails).
+ """
+ defmacro tmp_dir do
+ test = Module.get_attribute(__CALLER__.module, :ex_unit_test)
+
+ unless test do
+ raise "cannot invoke tmp_dir/0 outside of a test. Please make sure you have invoked " <>
+ "\"use ExUnit.Case\" in the current module"
+ end
+
+ path = Path.join([System.tmp_dir(), "#{inspect(test.module)}_#{test.name}"])
+ tmp_dirs = Module.get_attribute(__CALLER__.module, :ex_unit_tmp_dirs)
+
+ if test.name in tmp_dirs do
+ quote do
+ unquote(path)
+ end
+ else
+ Module.put_attribute(__CALLER__.module, :ex_unit_tmp_dirs, [test.name | tmp_dirs])
+
+ quote bind_quoted: [path: path] do
+ File.mkdir_p!(path)
+ on_exit(fn -> File.rm_rf!(path) end)
+ path
+ end
+ end
+ end
+end

lib/mix/test/mix/shell_test.exs

@@ -2,6 +2,7 @@ Code.require_file("../test_helper.exs", __DIR__)
 
 defmodule Mix.ShellTest do
  use MixTest.Case
+ import ExUnit.TmpDir
 
  defp capture_io(fun) do
  fun |> ExUnit.CaptureIO.capture_io() |> String.replace("\r\n", "\n")
@@ -20,12 +21,10 @@ defmodule Mix.ShellTest do
 
  test "with :cd" do
  Mix.shell(Mix.Shell.IO)
- tmp_dir = System.tmp_dir()
- File.mkdir_p!(tmp_dir)
- {pwd, 0} = System.cmd("pwd", [], cd: tmp_dir)
+ {pwd, 0} = System.cmd("pwd", [], cd: tmp_dir())
 
  assert ExUnit.CaptureIO.capture_io(fn ->
- Mix.shell().cmd("pwd", cd: tmp_dir)
+ Mix.shell().cmd("pwd", cd: tmp_dir())
  end) == pwd
  after
  Mix.shell(Mix.Shell.Process)