Add support for use_stdio option to System.shell and Mix.Shell.cmd

lib/elixir/lib/system.ex

@@ -1053,7 +1053,11 @@ defmodule System do
 
     * `:arg0` - sets the command arg0
 
-    * `:stderr_to_stdout` - redirects stderr to stdout when `true`
+    * `:stderr_to_stdout` - redirects stderr to stdout when `true`, no effect
+      if `use_stdio` is `false``.
+
+    * `:use_stdio` - `true` by default, setting it to false allows direct
+      interaction with the terminal from the callee
 
     * `:parallelism` - when `true`, the VM will schedule port tasks to improve
       parallelism in the system. If set to `false`, the VM will try to perform
@@ -1179,6 +1183,13 @@ defmodule System do
   defp cmd_opts([{:stderr_to_stdout, false} | t], opts, into, line),
     do: cmd_opts(t, opts, into, line)
 
+  defp cmd_opts([{:use_stdio, false} | t], opts, into, line),
+    do: cmd_opts(t, [:nouse_stdio | List.delete(opts, :use_stdio)], into, line)
+
+  # use_stdio is true by default, do nothing but match it
+  defp cmd_opts([{:use_stdio, true} | t], opts, into, line),
+    do: cmd_opts(t, opts, into, line)
+
   defp cmd_opts([{:parallelism, bool} | t], opts, into, line) when is_boolean(bool),
     do: cmd_opts(t, [{:parallelism, bool} | opts], into, line)
 
@@ -1192,8 +1203,12 @@ defmodule System do
   defp cmd_opts([{key, val} | _], _opts, _into, _line),
     do: raise(ArgumentError, "invalid option #{inspect(key)} with value #{inspect(val)}")
 
-  defp cmd_opts([], opts, into, line),
-    do: {into, line, opts}
+  defp cmd_opts([], opts, into, line) do
+    if :stderr_to_stdout in opts and :nouse_stdio in opts,
+      do: raise(ArgumentError, "cannot use `stderr_to_stdout: true` and `use_stdio: false`")
+
+    {into, line, opts}
+  end
 
   defp validate_env(enum) do
     Enum.map(enum, fn

lib/elixir/test/elixir/system_test.exs

@@ -110,7 +110,8 @@ defmodule SystemTest do
         env: %{"foo" => "bar", "baz" => nil},
         arg0: "echo",
         stderr_to_stdout: true,
-        parallelism: true
+        parallelism: true,
+        use_stdio: true
       ]
 
       assert {["hello\r\n"], 0} = System.cmd("cmd", ~w[/c echo hello], opts)
@@ -146,7 +147,8 @@ defmodule SystemTest do
         cd: File.cwd!(),
         env: %{"foo" => "bar", "baz" => nil},
         stderr_to_stdout: true,
-        parallelism: true
+        parallelism: true,
+        use_stdio: true
       ]
 
       assert {["bar\r\n"], 0} = System.shell("echo %foo%", opts)
@@ -167,12 +169,39 @@ defmodule SystemTest do
         env: %{"foo" => "bar", "baz" => nil},
         arg0: "echo",
         stderr_to_stdout: true,
-        parallelism: true
+        parallelism: true,
+        use_stdio: true
       ]
 
       assert {["hello\n"], 0} = System.cmd("echo", ["hello"], opts)
     end
 
+    test "cmd/3 (can't use `use_stdio: false, stderr_to_stdout: true`)" do
+      opts = [
+        into: [],
+        cd: File.cwd!(),
+        env: %{"foo" => "bar", "baz" => nil},
+        arg0: "echo",
+        stderr_to_stdout: true,
+        use_stdio: false
+      ]
+
+      message = ~r"cannot use `stderr_to_stdout: true` and `use_stdio: false`"
+
+      assert_raise ArgumentError, message, fn ->
+        System.cmd("echo", ["hello"], opts)
+      end
+    end
+
+    test "cmd/3 (`use_stdio: false`)" do
+      opts = [
+        into: [],
+        use_stdio: false
+      ]
+
+      assert {[], 0} = System.cmd("echo", ["hello"], opts)
+    end
+
     test "cmd/3 by line" do
       assert {["hello", "world"], 0} =
                System.cmd("echo", ["hello\nworld"], into: [], lines: 1024)
@@ -228,11 +257,16 @@ defmodule SystemTest do
         into: [],
         cd: File.cwd!(),
         env: %{"foo" => "bar", "baz" => nil},
-        stderr_to_stdout: true
+        stderr_to_stdout: true,
+        use_stdio: true
       ]
 
       assert {["bar\n"], 0} = System.shell("echo $foo", opts)
     end
+
+    test "shell/2 (non-interactive)" do
+      assert {[], 0} = System.shell("echo hello", into: [], use_stdio: false)
+    end
   end
 
   @tag :unix

lib/mix/lib/mix/shell.ex

@@ -103,7 +103,9 @@ defmodule Mix.Shell do
 
     * `:cd` *(since v1.11.0)* - the directory to run the command in
 
-    * `:stderr_to_stdout` - redirects stderr to stdout, defaults to true
+    * `:stderr_to_stdout` - redirects stderr to stdout, defaults to true, unless use_stdio is set to false
+
+    * `:use_stdio` - controls whether the command should use stdin / stdout / stdrr, defaults to true
 
     * `:env` - a list of environment variables, defaults to `[]`
 
@@ -119,11 +121,13 @@ defmodule Mix.Shell do
         callback
       end
 
+    use_stdio = Keyword.get(options, :use_stdio, true)
+
     options =
       options
-      |> Keyword.take([:cd, :stderr_to_stdout, :env])
+      |> Keyword.take([:cd, :stderr_to_stdout, :env, :use_stdio])
       |> Keyword.put(:into, %Mix.Shell{callback: callback})
-      |> Keyword.put_new(:stderr_to_stdout, true)
+      |> Keyword.put_new(:stderr_to_stdout, use_stdio)
 
     {_, status} = System.shell(command, options)
     status