Extend the interface of the isolation provider

Add the following two methods in the isolation provider:
1. `.is_available()`: Mainly used for the Container isolation provider,
   it specifies whether the container runtime is up and running. May be
   used in the future by other similar providers.
2. `.should_wait_install()`: Whether the isolation provider takes a
   while to be installed. Should be `True` only for the Container
   isolation provider, for the time being.

dangerzone/gui/main_window.py

@@ -26,12 +26,10 @@ else:
 from .. import errors
 from ..document import SAFE_EXTENSION, Document
 from ..isolation_provider.container import (
-    Container,
     NoContainerTechException,
     NotAvailableContainerTechException,
 )
-from ..isolation_provider.dummy import Dummy
-from ..isolation_provider.qubes import Qubes, is_qubes_native_conversion
+from ..isolation_provider.qubes import is_qubes_native_conversion
 from ..util import format_exception, get_resource_path, get_version
 from .logic import Alert, CollapsibleBox, DangerzoneGui, UpdateDialog
 from .updater import UpdateReport
@@ -197,14 +195,11 @@ class MainWindow(QtWidgets.QMainWindow):
         header_layout.addWidget(self.hamburger_button)
         header_layout.addSpacing(15)
 
-        if isinstance(self.dangerzone.isolation_provider, Container):
+        if self.dangerzone.isolation_provider.should_wait_install():
             # Waiting widget replaces content widget while container runtime isn't available
             self.waiting_widget: WaitingWidget = WaitingWidgetContainer(self.dangerzone)
             self.waiting_widget.finished.connect(self.waiting_finished)
-
-        elif isinstance(self.dangerzone.isolation_provider, Dummy) or isinstance(
-            self.dangerzone.isolation_provider, Qubes
-        ):
+        else:
             # Don't wait with dummy converter and on Qubes.
             self.waiting_widget = WaitingWidget()
             self.dangerzone.is_waiting_finished = True
@@ -500,8 +495,7 @@ class WaitingWidgetContainer(WaitingWidget):
         error: Optional[str] = None
 
         try:
-            assert isinstance(self.dangerzone.isolation_provider, (Dummy, Container))
-            self.dangerzone.isolation_provider.is_runtime_available()
+            self.dangerzone.isolation_provider.is_available()
         except NoContainerTechException as e:
             log.error(str(e))
             state = "not_installed"

dangerzone/isolation_provider/base.py

@@ -254,6 +254,16 @@ class IsolationProvider(ABC):
             )
         return errors.exception_from_error_code(error_code)
 
+    @abstractmethod
+    def should_wait_install(self) -> bool:
+        """Whether this isolation provider takes a lot of time to install."""
+        pass
+
+    @abstractmethod
+    def is_available(self) -> bool:
+        """Whether the backing implementation of the isolation provider is available."""
+        pass
+
     @abstractmethod
     def get_max_parallel_conversions(self) -> int:
         pass

dangerzone/isolation_provider/container.py

@@ -304,7 +304,11 @@ class Container(IsolationProvider):
         return True
 
     @staticmethod
-    def is_runtime_available() -> bool:
+    def should_wait_install() -> bool:
+        return True
+
+    @staticmethod
+    def is_available() -> bool:
         container_runtime = Container.get_runtime()
         runtime_name = Container.get_runtime_name()
         # Can we run `docker/podman image ls` without an error

dangerzone/isolation_provider/dummy.py

@@ -40,9 +40,13 @@ class Dummy(IsolationProvider):
         return True
 
     @staticmethod
-    def is_runtime_available() -> bool:
+    def is_available() -> bool:
         return True
 
+    @staticmethod
+    def should_wait_install() -> bool:
+        return False
+
     def start_doc_to_pixels_proc(self, document: Document) -> subprocess.Popen:
         cmd = [
             sys.executable,

dangerzone/isolation_provider/qubes.py

@@ -21,6 +21,14 @@ class Qubes(IsolationProvider):
     def install(self) -> bool:
         return True
 
+    @staticmethod
+    def is_available() -> bool:
+        return True
+
+    @staticmethod
+    def should_wait_install() -> bool:
+        return False
+
     def get_max_parallel_conversions(self) -> int:
         return 1
 

tests/gui/test_main_window.py

@@ -512,7 +512,7 @@ def test_not_available_container_tech_exception(
     # Setup
     mock_app = mocker.MagicMock()
     dummy = Dummy()
-    fn = mocker.patch.object(dummy, "is_runtime_available")
+    fn = mocker.patch.object(dummy, "is_available")
     fn.side_effect = NotAvailableContainerTechException(
         "podman", "podman image ls logs"
     )
@@ -536,7 +536,7 @@ def test_no_container_tech_exception(qtbot: QtBot, mocker: MockerFixture) -> Non
     dummy = mocker.MagicMock()
 
     # Raise
-    dummy.is_runtime_available.side_effect = NoContainerTechException("podman")
+    dummy.is_available.side_effect = NoContainerTechException("podman")
 
     dz = DangerzoneGui(mock_app, dummy)
     widget = WaitingWidgetContainer(dz)

tests/isolation_provider/test_container.py

@@ -27,9 +27,7 @@ def provider() -> Container:
 
 
 class TestContainer(IsolationProviderTest):
-    def test_is_runtime_available_raises(
-        self, provider: Container, fp: FakeProcess
-    ) -> None:
+    def test_is_available_raises(self, provider: Container, fp: FakeProcess) -> None:
         """
         NotAvailableContainerTechException should be raised when
         the "podman image ls" command fails.
@@ -40,18 +38,16 @@ class TestContainer(IsolationProviderTest):
             stderr="podman image ls logs",
         )
         with pytest.raises(NotAvailableContainerTechException):
-            provider.is_runtime_available()
+            provider.is_available()
 
-    def test_is_runtime_available_works(
-        self, provider: Container, fp: FakeProcess
-    ) -> None:
+    def test_is_available_works(self, provider: Container, fp: FakeProcess) -> None:
         """
         No exception should be raised when the "podman image ls" can return properly.
         """
         fp.register_subprocess(
             [provider.get_runtime(), "image", "ls"],
         )
-        provider.is_runtime_available()
+        provider.is_available()
 
     def test_install_raise_if_image_cant_be_installed(
         self, mocker: MockerFixture, provider: Container, fp: FakeProcess