package: Fail diagnostic when not able to resolve

When a package expression cannot be resolved (i.e. not installable),
add a diagnostic failure result with appropriate message.

Signed-off-by: James Valleroy <jvalleroy@mailbox.org>

plinth/package.py

@@ -56,6 +56,9 @@ class Package(PackageExpression):
         self.codename = codename
         self.architecture = architecture
 
+    def __repr__(self):
+        return self.name
+
     def __or__(self, other):
         return PackageOr(self, other)
 
@@ -79,6 +82,9 @@ class PackageOr(PackageExpression):
         self.package1 = package1
         self.package2 = package2
 
+    def __repr__(self):
+        return self.package1.name + ' | ' + self.package2.name
+
     def possible(self) -> list[str]:
         return self.package1.possible() + self.package2.possible()
 
@@ -169,8 +175,15 @@ class Packages(app.FollowerComponent):
         """Run diagnostics and return results."""
         results = super().diagnose()
         cache = apt.Cache()
-        # XXX: Needs to be able to handle missing packages.
-        for package_name in self.resolve():
+        for package_expression in self.packages:
+            try:
+                package_name = package_expression.actual()
+            except MissingPackageError:
+                message = _('Package {expression} is not available for '
+                            'install').format(expression=package_expression)
+                results.append([message, 'failed'])
+                continue
+
             result = 'warning'
             latest_version = '?'
             if package_name in cache:

plinth/tests/test_package.py

@@ -126,16 +126,24 @@ def test_diagnose(cache):
     cache.return_value = {
         'package2': Mock(candidate=Mock(version='2.0', is_installed=True)),
         'package3': Mock(candidate=Mock(version='3.0', is_installed=False)),
+        'package7': Mock(candidate=Mock(version='4.0', is_installed=True)),
     }
-    component = Packages('test-component',
-                         ['package1', 'package2', 'package3'])
+    component = Packages('test-component', [
+        'package1', 'package2', 'package3',
+        Package('package4') | Package('package5'),
+        Package('package6') | Package('package7')
+    ])
     results = component.diagnose()
-    assert '(?)' in results[0][0]
-    assert results[0][1] == 'warning'
+    assert 'not available for install' in results[0][0]
+    assert results[0][1] == 'failed'
     assert '(2.0)' in results[1][0]
     assert results[1][1] == 'passed'
     assert '(3.0)' in results[2][0]
     assert results[2][1] == 'warning'
+    assert 'not available for install' in results[3][0]
+    assert results[3][1] == 'failed'
+    assert '(4.0)' in results[4][0]
+    assert results[4][1] == 'passed'
 
 
 @patch('plinth.package.packages_installed')