feat(provider): list provider instances

Fixes #639

craft_providers/lxd/lxd_instance.py

@@ -78,6 +78,9 @@ def __init__(
         else:
             self.lxc = lxc
 
+    def __repr__(self) -> str:
+        return f"{self.__class__.__name__}(name={self.name!r}, default_command_environment={self.default_command_environment!r}, project={self.project!r}, remote={self.remote!r})"
+
     def _set_instance_name(self) -> None:
         """Convert a name to a LXD-compatible name.
 

craft_providers/lxd/lxd_provider.py

@@ -19,6 +19,7 @@
 import contextlib
 import logging
 import pathlib
+from collections.abc import Collection
 from datetime import timedelta
 from typing import Iterator
 
@@ -87,6 +88,15 @@ def is_provider_installed(cls) -> bool:
         """
         return is_installed()
 
+    def list_instances(self) -> Collection[LXDInstance]:
+        """Get a collection of existing instances for this LXD provider."""
+        return [
+            LXDInstance(name=name, project=self.lxd_project, remote=self.lxd_remote)
+            for name in self.lxc.list_names(
+                project=self.lxd_project, remote=self.lxd_remote
+            )
+        ]
+
     def create_environment(self, *, instance_name: str) -> Executor:
         """Create a bare environment for specified base.
 

craft_providers/multipass/multipass_instance.py

@@ -79,6 +79,9 @@ def __init__(
         else:
             self._multipass = Multipass()
 
+    def __repr__(self) -> str:
+        return f"{self.__class__.__name__}(name={self.name!r})"
+
     def _create_temp_file(self) -> str:
         """Create a temporary file inside the instance owned by the `ubuntu` user.
 

craft_providers/multipass/multipass_provider.py

@@ -19,6 +19,7 @@
 import contextlib
 import logging
 import pathlib
+from collections.abc import Collection
 from dataclasses import dataclass
 from enum import Enum
 from typing import Dict, Iterator
@@ -164,6 +165,13 @@ def ensure_provider_is_available(cls) -> None:
             install()
         ensure_multipass_is_ready()
 
+    def list_instances(self) -> Collection[MultipassInstance]:
+        """Get a collection of existing multipass VMs."""
+        return [
+            MultipassInstance(name=name, multipass=self.multipass)
+            for name in self.multipass.list()
+        ]
+
     def create_environment(self, *, instance_name: str) -> Executor:
         """Create a bare environment for specified base.
 

craft_providers/provider.py

@@ -25,6 +25,7 @@
 import logging
 import pathlib
 from abc import ABC, abstractmethod
+from collections.abc import Collection
 from typing import Generator
 
 from .base import Base
@@ -78,6 +79,10 @@ def is_provider_installed(cls) -> bool:
         :returns: True if installed.
         """
 
+    @abstractmethod
+    def list_instances(self) -> Collection[Executor]:
+        """Get a collection of existing instances for this provider."""
+
     @abstractmethod
     def create_environment(self, *, instance_name: str) -> Executor:
         """Create a bare environment for specified base.