entry: lazy load subcommands

src/nomad_tools/entry.py

@@ -3,26 +3,9 @@
 import clickforward
 from click.shell_completion import BashComplete
 
-from . import (
-    entry_constrainteval,
-    entry_cp,
-    entry_dockers,
-    entry_downloadrelease,
-    entry_githubrunner,
-    entry_gitlab_runner,
-    entry_go,
-    entry_listattributes,
-    entry_listnodeattributes,
-    entry_nodenametoid,
-    entry_port,
-    entry_task,
-    entry_info,
-    entry_vardir,
-    entry_watch,
-)
+from .lazygroup import LazyGroup
 from .common_click import EPILOG, common_options, main_options
 from .common_nomad import namespace_option
-from .aliasedgroup import AliasedGroup
 
 clickforward.init()
 
@@ -60,10 +43,30 @@
     %(complete_func)s_setup;
 """
 
+subcommands = """
+    constrainteval
+    cp
+    dockers
+    downloadrelease
+    githubrunner
+    gitlab_runner
+    go
+    listattributes
+    listnodeattributes
+    nodenametoid
+    port
+    task
+    info
+    vardir
+    watch
+    """.split()
+
+
 
 @click.command(
     "nomadtools",
-    cls=AliasedGroup,
+    cls=LazyGroup,
+    lazy_subcommands={cmd: f"{__package__}.entry_{cmd}.cli" for cmd in subcommands},
     help="Collection of useful tools for HashiCorp Nomad.",
     epilog=EPILOG,
 )
@@ -74,23 +77,6 @@ def cli():
     pass
 
 
-cli.add_command(entry_constrainteval.cli)
-cli.add_command(entry_cp.cli)
-cli.add_command(entry_dockers.cli)
-cli.add_command(entry_downloadrelease.cli)
-cli.add_command(entry_githubrunner.cli)
-cli.add_command(entry_gitlab_runner.cli)
-cli.add_command(entry_go.cli)
-cli.add_command(entry_listattributes.cli)
-cli.add_command(entry_listnodeattributes.cli)
-cli.add_command(entry_nodenametoid.cli)
-cli.add_command(entry_port.cli)
-cli.add_command(entry_info.cli)
-cli.add_command(entry_task.cli)
-cli.add_command(entry_vardir.cli)
-cli.add_command(entry_watch.cli)
-
-
 def main():
     cli(max_content_width=9999)
 

src/nomad_tools/lazygroup.py

@@ -0,0 +1,40 @@
+# https://click.palletsprojects.com/en/8.1.x/complex/#defining-the-lazy-group
+import importlib
+import click
+from .aliasedgroup import AliasedGroup
+
+
+class LazyGroup(AliasedGroup):
+    def __init__(self, *args, lazy_subcommands=None, **kwargs):
+        super().__init__(*args, **kwargs)
+        # lazy_subcommands is a map of the form:
+        #
+        #   {command-name} -> {module-name}.{command-object-name}
+        #
+        self.lazy_subcommands = lazy_subcommands or {}
+
+    def list_commands(self, ctx):
+        base = super().list_commands(ctx)
+        lazy = sorted(self.lazy_subcommands.keys())
+        return base + lazy
+
+    def get_command(self, ctx, cmd_name):
+        if cmd_name in self.lazy_subcommands:
+            return self._lazy_load(cmd_name)
+        return super().get_command(ctx, cmd_name)
+
+    def _lazy_load(self, cmd_name):
+        # lazily loading a command, first get the module name and attribute name
+        import_path = self.lazy_subcommands[cmd_name]
+        modname, cmd_object_name = import_path.rsplit(".", 1)
+        # do the import
+        mod = importlib.import_module(modname)
+        # get the Command object from that module
+        cmd_object = getattr(mod, cmd_object_name)
+        # check the result to make debugging easier
+        if not isinstance(cmd_object, click.BaseCommand):
+            raise ValueError(
+                f"Lazy loading of {import_path} failed by returning "
+                "a non-command object"
+            )
+        return cmd_object