Gracefully ignore bad remove-project line

Sometimes, we don't care if the remove project is referring to a
non-existing project and we can just ignore it.  This change allows us
to ignore remove-project entries if the project that they refer to
doesn't exist, making them effectively a no-op.

Because this change breaks existing configuration, we allow this to be
configuration controlled using the `optional` attribute in the
remove-project tag.

Change-Id: I6313a02983e81344eadcb4e47d7d6b037ee7420e
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/310964
Tested-by: Michael Kelly <mkelly@arista.com>
Reviewed-by: Mike Frysinger <vapier@google.com>

docs/manifest-format.md

@@ -96,6 +96,7 @@ following DTD:
 
   <!ELEMENT remove-project EMPTY>
   <!ATTLIST remove-project name  CDATA #REQUIRED>
+  <!ATTLIST remove-project optional  CDATA #IMPLIED>
 
   <!ELEMENT repo-hooks EMPTY>
   <!ATTLIST repo-hooks in-project CDATA #REQUIRED>
@@ -393,6 +394,9 @@ This element is mostly useful in a local manifest file, where
 the user can remove a project, and possibly replace it with their
 own definition.
 
+Attribute `optional`: Set to true to ignore remove-project elements with no
+matching `project` element.
+
 ### Element repo-hooks
 
 NB: See the [practical documentation](./repo-hooks.md) for using repo hooks.

manifest_xml.py

@@ -918,10 +918,7 @@ https://gerrit.googlesource.com/git-repo/+/HEAD/docs/manifest-format.md
       if node.nodeName == 'remove-project':
         name = self._reqatt(node, 'name')
 
-        if name not in self._projects:
+        if name in self._projects:
-          raise ManifestParseError('remove-project element specifies non-existent '
-                                   'project: %s' % name)
-
           for p in self._projects[name]:
             del self._paths[p.relpath]
           del self._projects[name]
@@ -930,6 +927,9 @@ https://gerrit.googlesource.com/git-repo/+/HEAD/docs/manifest-format.md
           # the repo-hooks element too.
           if self._repo_hooks_project and (self._repo_hooks_project.name == name):
             self._repo_hooks_project = None
+        elif not XmlBool(node, 'optional', False):
+          raise ManifestParseError('remove-project element specifies non-existent '
+                                   'project: %s' % name)
 
   def _AddMetaProjectMirror(self, m):
     name = None

tests/test_manifest_xml.py

@@ -638,3 +638,53 @@ class RemoteElementTests(ManifestParseTestCase):
     self.assertNotEqual(a, manifest_xml._Default())
     self.assertNotEqual(a, 123)
     self.assertNotEqual(a, None)
+
+
+class RemoveProjectElementTests(ManifestParseTestCase):
+  """Tests for <remove-project>."""
+
+  def test_remove_one_project(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="myproject" />
+  <remove-project name="myproject" />
+</manifest>
+""")
+    self.assertEqual(manifest.projects, [])
+
+  def test_remove_one_project_one_remains(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="myproject" />
+  <project name="yourproject" />
+  <remove-project name="myproject" />
+</manifest>
+""")
+
+    self.assertEqual(len(manifest.projects), 1)
+    self.assertEqual(manifest.projects[0].name, 'yourproject')
+
+  def test_remove_one_project_doesnt_exist(self):
+    with self.assertRaises(manifest_xml.ManifestParseError):
+      manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <remove-project name="myproject" />
+</manifest>
+""")
+      manifest.projects
+
+  def test_remove_one_optional_project_doesnt_exist(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <remove-project name="myproject" optional="true" />
+</manifest>
+""")
+    self.assertEqual(manifest.projects, [])