Callable alias: fixed capturing stdout in case of redirect (#5527)

### Motivation

Closes #5512. 
The issue was introduced in #4445. It's needed to add checking the
redirect case.

### Before

```xsh
cd /tmp
@aliases.register('a')
def _a():
    print("1-hello")
    echo 2-hello
a > o.txt
# 2-hello
cat o.txt
# 1-hello
```

### After

```xsh
cd /tmp
@aliases.register('a')
def _a():
    print("1-hello")
    echo 2-hello
a > o.txt
cat o.txt
# 1-hello
# 2-hello
```

## For community
⬇️ **Please click the 👍 reaction instead of leaving a `+1` or 👍
comment**

---------

Co-authored-by: a <1@1.1>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

news/callias_capture_redirect.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* Callable alias: fixed capturing stdout in case of redirect e.g. `a > file` (#5527).
+
+**Security:**
+
+* <news item>

tests/procs/test_specs.py

@@ -150,6 +150,25 @@ def test_capture_always(
     assert exp in capfd.readouterr().out
 
 
+@skip_if_on_windows
+@pytest.mark.flaky(reruns=3, reruns_delay=2)
+def test_callias_captured_redirect(xonsh_session, tmpdir):
+    @xonsh_session.aliases.register("a")
+    def _a(a, i, o, e):
+        print("print_stdout")
+        xonsh_session.subproc_captured_stdout(["echo", "cap_stdout"])
+        xonsh_session.subproc_captured_object(["echo", "cap_object"])
+        xonsh_session.subproc_captured_hiddenobject(["echo", "hiddenobject"])
+        xonsh_session.subproc_uncaptured(["echo", "uncaptured"])
+        print("print_error", file=e)
+
+    f = tmpdir / "capture.txt"
+    cmd = (["a", (">", str(f))],)
+    specs = cmds_to_specs(cmd, captured="hiddenobject")
+    _run_command_pipeline(specs, cmd).end()
+    assert f.read_text(encoding="utf-8") == "print_stdout\nhiddenobject\n"
+
+
 @skip_if_on_windows
 @pytest.mark.parametrize("captured", ["stdout", "object"])
 @pytest.mark.parametrize("interactive", [True, False])

xonsh/procs/specs.py

@@ -1021,19 +1021,30 @@ def cmds_to_specs(cmds, captured=False, envs=None):
 
     # Apply boundary conditions
     if not XSH.env.get("XONSH_CAPTURE_ALWAYS"):
-        # Make sure sub-specs are always captured.
-        # I.e. ![some_alias | grep x] $(some_alias)
-        specs_to_capture = specs if captured in STDOUT_CAPTURE_KINDS else specs[:-1]
-        for spec in specs_to_capture:
-            if spec.env is None:
-                spec.env = {"XONSH_CAPTURE_ALWAYS": True}
-            else:
-                spec.env.setdefault("XONSH_CAPTURE_ALWAYS", True)
+        # Make sure sub-specs are always captured in case:
+        # `![some_alias | grep x]`, `$(some_alias)`, `some_alias > file`.
+        last = spec
+        is_redirected_stdout = bool(last.stdout)
+        specs_to_capture = (
+            specs
+            if captured in STDOUT_CAPTURE_KINDS or is_redirected_stdout
+            else specs[:-1]
+        )
+        _set_specs_capture_always(specs_to_capture)
 
     _update_last_spec(specs[-1])
     return specs
 
 
+def _set_specs_capture_always(specs_to_capture):
+    """Set XONSH_CAPTURE_ALWAYS for all specs."""
+    for spec in specs_to_capture:
+        if spec.env is None:
+            spec.env = {"XONSH_CAPTURE_ALWAYS": True}
+        else:
+            spec.env.setdefault("XONSH_CAPTURE_ALWAYS", True)
+
+
 def _shell_set_title(cmds):
     if XSH.env.get("XONSH_INTERACTIVE") and XSH.shell is not None:
         # context manager updates the command information that gets