Revert partial_proxy (#5445)

In #5366 we removed partial_proxy. But @doronz88 [found the
case](https://xonsh.zulipchat.com/#narrow/stream/435525-xonsh-xontrib/topic/.E2.9C.94.20xontrib-z.20and.20maybe.20other.20break.20in.20master)
where this functionality is good and needed. In xontrib-z there is a
[handler](a40abb4d8b/xontrib/z.py (L225-L227))
that requires partial_proxy. So I bring partial_proxy back because it
looks useful.

## 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>

tests/procs/test_specs.py

@@ -308,3 +308,15 @@ def test_redirect_to_substitution(xession):
         ["echo", "hello", (">", ["file"])]
     )
     assert s.stdout.name == "file"
+
+
+def test_partial_args_from_classmethod(xession):
+    class Class:
+        @classmethod
+        def alias(cls, args, stdin, stdout):
+            print("ok", file=stdout)
+            return 0
+
+    xession.aliases["alias_with_partial_args"] = Class.alias
+    out = run_subproc([["alias_with_partial_args"]], captured="stdout")
+    assert out == "ok"

tests/test_history_json.py

@@ -340,7 +340,7 @@ def test_parser_show(args, session, slice, numerate, reverse, mocker, hist, xess
     from xonsh.history import main as mod
 
     main = HistoryAlias()
-    spy = mocker.spy(mod.xcli, "_dispatch_func")
+    spy = mocker.spy(mod.xcli, "run_with_partial_args")
 
     # action
     main(shlex.split(args))

xonsh/cli_utils.py

@@ -366,8 +366,8 @@ class ArgParser(ap.ArgumentParser):
         return super()._parse_known_args(arg_strings, namespace)
 
 
-def _dispatch_func(func: tp.Callable, ns: dict[str, tp.Any]):
+def run_with_partial_args(func: tp.Callable, ns: dict[str, tp.Any]):
-    """Final dispatch to the function based on signature."""
+    """Run function based on signature. Filling the arguments will be based on the values in ``ns``."""
     sign = inspect.signature(func)
     kwargs = {}
     for name, param in sign.parameters.items():
@@ -408,7 +408,7 @@ def dispatch(parser: ap.ArgumentParser, args=None, lenient=False, **ns):
 
     if _FUNC_NAME in ns:
         func = ns[_FUNC_NAME]
-        return _dispatch_func(func, ns)
+        return run_with_partial_args(func, ns)
 
 
 class ArgparseCompleter:

xonsh/procs/proxies.py

@@ -20,6 +20,7 @@ import xonsh.lazyimps as xli
 import xonsh.platform as xp
 import xonsh.tools as xt
 from xonsh.built_ins import XSH
+from xonsh.cli_utils import run_with_partial_args
 from xonsh.procs.readers import safe_fdclose
 
 
@@ -466,7 +467,17 @@ class ProcProxyThread(threading.Thread):
                 xt.redirect_stderr(STDERR_DISPATCHER),
                 XSH.env.swap(self.env, __ALIAS_STACK=alias_stack),
             ):
-                r = self.f(self.args, sp_stdin, sp_stdout, sp_stderr, spec, spec.stack)
+                r = run_with_partial_args(
+                    self.f,
+                    {
+                        "args": self.args,
+                        "stdin": sp_stdin,
+                        "stdout": sp_stdout,
+                        "stderr": sp_stderr,
+                        "spec": spec,
+                        "stack": spec.stack,
+                    },
+                )
         except SystemExit as e:
             r = e.code if isinstance(e.code, int) else int(bool(e.code))
         except OSError:
@@ -767,7 +778,17 @@ class ProcProxy:
         # run the actual function
         try:
             with XSH.env.swap(self.env):
-                r = self.f(self.args, stdin, stdout, stderr, spec, spec.stack)
+                r = run_with_partial_args(
+                    self.f,
+                    {
+                        "args": self.args,
+                        "stdin": stdin,
+                        "stdout": stdout,
+                        "stderr": stderr,
+                        "spec": spec,
+                        "stack": spec.stack,
+                    },
+                )
         except Exception:
             xt.print_exception(source_msg="Exception in " + get_proc_proxy_name(self))
             r = 1