[WIP] testing subcommands with pluggy

dvc/cli/parser.py

@@ -200,6 +200,13 @@ def get_main_parser():
         type=str,
     )
 
+    parser.add_argument(
+        "--plugins",
+        metavar="<path>",
+        default=None,
+        help="Path to a plugins directory",
+    )
+
     # Sub commands
     subparsers = parser.add_subparsers(
         title="Available Commands",
@@ -215,4 +222,9 @@ def get_main_parser():
     for cmd in COMMANDS:
         cmd.add_parser(subparsers, parent_parser)
 
+    from dvc.plugins import plugin_manager
+
+    plugin_manager.hook.register_command(  # pylint: disable=no-member
+        parser=subparsers, parent=parent_parser
+    )
     return parser

dvc/env.py

@@ -10,3 +10,4 @@
 DVC_EXP_GIT_REMOTE = "DVC_EXP_GIT_REMOTE"
 DVC_EXP_AUTO_PUSH = "DVC_EXP_AUTO_PUSH"
 DVC_NO_ANALYTICS = "DVC_NO_ANALYTICS"
+DVC_PLUGINS_DIR = "DVC_PLUGINS_DIR"

dvc/hookspecs.py

@@ -0,0 +1,9 @@
+from pluggy import HookimplMarker, HookspecMarker
+
+hookspec = HookspecMarker("dvc")
+hookimpl = HookimplMarker("dvc")
+
+
+@hookspec
+def register_command(parser, parent):  # pylint: disable=unused-argument
+    pass

dvc/plugins.py

@@ -0,0 +1,66 @@
+import glob
+import os
+import sys
+from typing import List
+
+import pluggy
+
+from . import hookspecs
+from .env import DVC_PLUGINS_DIR
+
+
+def import_file(name, file):
+    import importlib.util
+
+    spec = importlib.util.spec_from_file_location(name, file)
+    mod = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(mod)
+    return mod
+
+
+class PluginManager(pluggy.PluginManager):
+    def add_files_from_dir(self, directory: str) -> None:
+        if not os.path.isdir(directory):
+            return
+        path = os.path.join(directory, "*.py")
+        for file in filter(os.path.isfile, glob.glob(path)):
+            mod = import_file(os.path.basename(file)[:-3], file)
+            try:
+                self.register(mod)
+            except ValueError:
+                pass
+
+    def load_from_env(self, env: str = DVC_PLUGINS_DIR) -> None:
+        if env in os.environ:
+            self.add_files_from_dir(os.environ[env])
+
+    def load_from_args(
+        self, args: List[str] = None, opt_name: str = "--plugins"
+    ) -> None:
+        args = sys.argv[1:] if args is None else args
+        i = 0
+        n = len(args)
+        while i < n:
+            opt = args[i]
+            i += 1
+            if isinstance(opt, str):
+                if opt == opt_name:
+                    try:
+                        parg = args[i]
+                    except IndexError:
+                        return
+                    i += 1
+                elif opt.startswith(f"{opt_name}="):
+                    parg = opt[len(f"{opt_name}=") :]
+                else:
+                    continue
+                self.add_files_from_dir(parg)
+
+
+plugin_manager = PluginManager("dvc")
+plugin_manager.add_hookspecs(hookspecs)
+
+if "DVC_TEST" not in os.environ:  # we don't want to run this on tests
+    plugin_manager.load_setuptools_entrypoints("dvc")
+    plugin_manager.load_from_args()
+    plugin_manager.load_from_env()

plugins/hello.py

@@ -0,0 +1,21 @@
+from argparse import Namespace
+from dataclasses import dataclass
+
+from dvc.hookspecs import hookimpl
+
+
+@dataclass
+class HelloCommand:
+    args: Namespace
+
+    def do_run(self):
+        print("Hello, world!")
+        return 0
+
+
+@hookimpl
+def register_command(parser, parent):
+    hello_world = parser.add_parser(
+        "hello", parents=[parent], help="print hello world"
+    )
+    hello_world.set_defaults(func=HelloCommand)

setup.cfg

@@ -76,6 +76,7 @@ install_requires =
     diskcache>=5.2.1
     jaraco.windows>=5.7.0; python_version < '3.8' and sys_platform == 'win32'
     scmrepo==0.0.7
+    pluggy>=1,<2
 
 [options.extras_require]
 all =