fix: install gpg and dirmngr in core24 builds

This commit mimicks the behavior for core22<= builds where gpg and dirmngr
are installed at runtime for projects with package-repositories. The trigger
for this commit is the fact that the environment where Snapcraft builds in
Launchpad do _not_ have the 'dirmngr' package installed.

Unfortunately the strategy of bundling 'gpg' and 'dirmngr' as stage-packages
in Snapcraft's own snap didn't work because gpg has the expected path to the
'dirmngr' executable hardcoded (always trying to call '/usr/bin/dirmngr').

Fixes #4740

snapcraft/services/lifecycle.py

@@ -25,6 +25,7 @@
 from craft_application import AppMetadata, LifecycleService, ServiceFactory
 from craft_application.models import BuildInfo
 from craft_parts import ProjectInfo, StepInfo
+from craft_parts.packages import Repository as Repo
 from overrides import overrides
 
 from snapcraft import __version__, errors, models, os_release, parts, utils
@@ -60,6 +61,14 @@ def __init__(  # noqa: PLR0913 (too many arguments)
     def setup(self) -> None:
         project = cast(models.Project, self._project)
 
+        if project.package_repositories:
+            # Note: we unfortunately need to handle missing gpg/dirmngr binaries
+            # ourselves here, as this situation happens in Launchpad (where
+            # builds are executed destructively).
+            required_packages = ["gpg", "dirmngr"]
+            if any(p for p in required_packages if not Repo.is_package_installed(p)):
+                Repo.install_packages(required_packages, refresh_package_cache=False)
+
         # Have the lifecycle install the base snap, and look into it when
         # determining the package cutoff.
         self._manager_kwargs.update(

tests/spread/core24/package-repositories/task.yaml

@@ -10,7 +10,14 @@ environment:
   SNAP/test_foreign_armhf: test-foreign-armhf
   SNAP/test_foreign_i386: test-foreign-i386
 
+prepare: |
+  # Remove the currently installed "gpg" and "dirmngr" packages to ensure that
+  # Snapcraft itself is installing them when necessary.
+  sudo dpkg --remove --force-depends gpg dirmngr
+
 restore: |
+  sudo apt install -y gpg dirmngr
+
   cd "$SNAP"
   rm -f ./*.snap
   snapcraft clean

tests/unit/services/test_lifecycle.py

@@ -23,6 +23,7 @@
 
 import pytest
 import pytest_subprocess
+from craft_parts.packages import Repository
 
 from snapcraft import __version__, models, os_release, utils
 
@@ -198,3 +199,24 @@ def test_lifecycle_prime_dirs(lifecycle_service):
     lifecycle_service.setup()
 
     assert lifecycle_service.prime_dirs == {None: lifecycle_service._work_dir / "prime"}
+
+
+@pytest.fixture()
+def package_repositories_params(extra_project_params):
+    """Add package-repositories configuration to the default project."""
+    extra_project_params["package_repositories"] = [{"type": "apt", "ppa": "test/ppa"}]
+
+
+@pytest.mark.usefixtures("package_repositories_params", "default_project")
+def test_lifecycle_installs_gpg_dirmngr(lifecycle_service, mocker):
+    mock_is_installed = mocker.patch.object(
+        Repository, "is_package_installed", return_value=False
+    )
+    mock_install = mocker.patch.object(Repository, "install_packages")
+
+    lifecycle_service.setup()
+
+    assert mock_is_installed.called
+    mock_install.assert_called_once_with(
+        ["gpg", "dirmngr"], refresh_package_cache=False
+    )