feat(extensions): support filtering by base

snapcraft/commands/extensions.py

@@ -28,7 +28,7 @@
 from pydantic import BaseModel
 from typing_extensions import override
 
-from snapcraft import errors, extensions, models
+from snapcraft import const, errors, extensions, models
 from snapcraft.parts.yaml_utils import (
     apply_yaml,
     extract_parse_info,
@@ -55,23 +55,45 @@ def marshal(self) -> dict[str, str]:
 
 
 class ExtensionsCommand(AppCommand):
-    """List available extensions for all supported bases."""
+    """List available extensions."""
 
     name = "extensions"
-    help_msg = "List available extensions for all supported bases."
+    help_msg = "List available extensions, optionally for a given base."
     overview = textwrap.dedent(
         """
-        List available extensions and their corresponding bases.
+        List available extensions, optionally for a given base.
         """
     )
 
+    @override
+    def fill_parser(self, parser: argparse.ArgumentParser) -> None:
+        """Add arguments specific to the extensions command."""
+        parser.add_argument(
+            "--base",
+            metavar="base",
+            type=str,
+            help="Show extensions for <base>",
+        )
+
     @override
     def run(self, parsed_args: argparse.Namespace) -> None:
+        base = getattr(parsed_args, "base", None)
+
+        if base in const.ESM_BASES:
+            raise errors.MaintenanceBase(base=base)
+
+        if base is not None and base not in const.CURRENT_BASES:
+            raise errors.SnapcraftError(f"{base} not supported")
+
         extension_presentation: dict[str, ExtensionModel] = {}
 
         for extension_name in extensions.registry.get_extension_names():
             extension_class = extensions.registry.get_extension_class(extension_name)
             extension_bases = list(extension_class.get_supported_bases())
+
+            if base is not None and base not in extension_bases:
+                continue
+
             extension_presentation[extension_name] = ExtensionModel(
                 name=extension_name, bases=extension_bases
             )

tests/unit/commands/test_list_extensions.py

@@ -57,6 +57,47 @@ def test_command(emitter, fake_app_config):
     )
 
 
+@pytest.mark.usefixtures("fake_extension")
+def test_command_base_option(emitter, fake_app_config):
+    cmd = snapcraft.commands.ExtensionsCommand(fake_app_config)
+
+    cmd.run(Namespace(base="core22"))
+
+    emitter.assert_message(
+        dedent(
+            """\
+        Extension name        Supported bases
+        --------------------  ----------------------
+        fake-extension        core22, core24, core26
+        gnome                 core22, core24
+        gpu                   core22, core24, core26
+        kde-neon              core22, core24
+        kde-neon-6            core22, core24
+        kde-neon-qt6          core22, core24
+        ros2-humble           core22
+        ros2-humble-desktop   core22
+        ros2-humble-ros-base  core22
+        ros2-humble-ros-core  core22"""
+        )
+    )
+
+
+def test_command_base_option_unsupported(fake_app_config):
+    cmd = snapcraft.commands.ExtensionsCommand(fake_app_config)
+
+    with pytest.raises(errors.SnapcraftError, match="core99 not supported"):
+        cmd.run(Namespace(base="core99"))
+
+
+def test_command_base_option_esm_base_error(fake_app_config):
+    cmd = snapcraft.commands.ExtensionsCommand(fake_app_config)
+
+    expected = re.escape("'core20' is not supported on this version of Snapcraft.")
+
+    with pytest.raises(errors.MaintenanceBase, match=expected):
+        cmd.run(Namespace(base="core20"))
+
+
 def test_list_extensions_error(fake_app_config):
     """Error on removed 'list-extensions' command."""
     cmd = snapcraft.commands.ListExtensionsCommand(fake_app_config)