Change !() to also capture background subprocesses (#4406)

* Change !() to also capture background subprocesses

* Add test

* Add news

* Simplify logic

news/capture-object-background.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* Changed !() to also capture background subprocesses
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>

tests/procs/test_specs.py

@@ -102,6 +102,23 @@ def test_capture_always(capfd, thread_subprocs, capture_always):
     assert exp in capfd.readouterr().out
 
 
+@skip_if_on_windows
+@pytest.mark.parametrize(
+    "captured, exp_is_none",
+    [
+        ("object", False),
+        ("stdout", True),
+        ("hiddenobject", True),
+        (False, True),
+    ],
+)
+def test_run_subproc_background(captured, exp_is_none):
+
+    cmds = (["echo", "hello"], "&")
+    return_val = run_subproc(cmds, captured)
+    assert (return_val is None) == exp_is_none
+
+
 @pytest.mark.parametrize("thread_subprocs", [False, True])
 def test_callable_alias_cls(thread_subprocs, xession):
     class Cls:

xonsh/procs/specs.py

@@ -892,15 +892,14 @@ def run_subproc(cmds, captured=False, envs=None):
         # sure that the shell doesn't hang. This `pause_call_resume` invocation
         # does this
         pause_call_resume(proc, int)
-    # create command or return if backgrounding.
-    if background:
+    # now figure out what we should return
+    if captured == "object":
+        return command  # object can be returned even if backgrounding
+    elif background:
         return
-    # now figure out what we should return.
-    if captured == "stdout":
+    elif captured == "stdout":
         command.end()
         return command.output
-    elif captured == "object":
-        return command
     elif captured == "hiddenobject":
         command.end()
         return command