instanced_inf_table: Account for non-existing library instance

Due to platforms performing complex includes in their DSCs, There is a
scenario in which a library instance references a library class that
does not exist. This is not an error as the library class instance may
not be consumed by a component in the platform, so the missing
dependency is acceptable.

This commit adds the ability to handle this scenario, and will not raise
an error for a missing library instance.

edk2toollib/database/tables/instanced_inf_table.py

@@ -119,6 +119,9 @@ def _parse_inf_recursively(
 
         Will immediately return if the INF has already been visited.
         """
+        if inf is None:
+            return []
+
         logging.debug(f"  Parsing Library: [{inf}]")
         visited.append(inf)
         library_instances = []
@@ -140,6 +143,8 @@ def _parse_inf_recursively(
         for null_lib in override_dict["NULL"]:
             library_instances.append(null_lib)
 
+        library_instances = list(filter(lambda lib: lib is not None, library_instances))
+
         # Time to visit in libraries that we have not visited yet.
         to_return = []
         for library in filter(lambda lib: lib not in visited, library_instances):
@@ -216,8 +221,8 @@ def _lib_to_instance(self, library_class_name, scope, library_dict, override_dic
         logging.debug(f'scoped library contents: {library_dict}')
         logging.debug(f'override dictionary: {override_dict}')
         e = f'Cannot find library class [{library_class_name}] for scope [{scope}] when evaluating {self.dsc}'
-        logging.error(e)
-        raise RuntimeError(e)
+        logging.warn(e)
+        return None
 
     def _reduce_lib_instances(self, module: str, library_instance_list: list[str]) -> str:
         """For a DSC, multiple library instances for the same library class can exist.

tests.unit/database/test_instanced_inf_table.py

@@ -209,7 +209,7 @@ def test_scoped_libraries2(empty_tree: Tree):
         if "COMPONENT" not in row:
             assert row["NAME"].replace("Driver", "Lib") in row["LIBRARIES_USED"][0]
 
-def test_missing_library(empty_tree: Tree):
+def test_missing_library(empty_tree: Tree, caplog):
     """Test when a library is missing."""
     edk2path = Edk2Path(str(empty_tree.ws), [])
     db = Edk2DB(Edk2DB.MEM_RW, pathobj=edk2path)
@@ -227,9 +227,13 @@ def test_missing_library(empty_tree: Tree):
         "TARGET_ARCH": "IA32 X64",
         "TARGET": "DEBUG",
     })
-    with pytest.raises(RuntimeError):
+
+    with caplog.at_level(logging.WARNING):
         inf_table.parse(db)
 
+        assert len(caplog.records) == 1
+        assert 'testcls' in caplog.records[0].message
+
 def test_skip_library_with_unsupported_module_type(empty_tree: Tree):
     """Library class INFs can specify what module types they support.