Add support for custom data

This patch implements proposal ST090. It allows to add custom
metadata into the snapcraft.yaml files without interferring
with snapcraft.

This is useful for adding extra data for tools that manage
snap files, like updatesnap.py, which searches for new versions
of the parts in a snapcraft.yaml file.

Proposal: https://docs.google.com/document/d/1QX0moP6V709D7L267pIT5AREQetbPb7KsFrpgvCLKVM

snapcraft/projects.py

@@ -32,6 +32,7 @@
     convert_architecture_deb_to_platform,
     get_effective_base,
     get_host_architecture,
+    remove_custom_data,
 )
 
 
@@ -639,6 +640,7 @@ def unmarshal(cls, data: Dict[str, Any]) -> "Project":
         if not isinstance(data, dict):
             raise TypeError("Project data is not a dictionary")
 
+        data = remove_custom_data(data)
         try:
             project = Project(**data)
         except pydantic.ValidationError as err:

snapcraft/utils.py

@@ -457,3 +457,22 @@ def process_version(version: Optional[str]) -> str:
 def is_snapcraft_running_from_snap() -> bool:
     """Check if snapcraft is running from the snap."""
     return os.getenv("SNAP_NAME") == "snapcraft" and os.getenv("SNAP") is not None
+
+def _remove_custom_data_from_dict(data):
+    prog = re.compile('^custom_data_[a-zA-Z0-9][a-zA-Z0-9_-]*$')
+    for element in list(data.keys()):
+        if prog.match(element) is not None:
+            data.pop(element)
+    return data
+
+def remove_custom_data(data):
+    # remove custom data from the root
+    data = _remove_custom_data_from_dict(data)
+
+    # remove custom data from apps, plugs, slots and parts
+    for entry_name in ["apps", "plugs", "slots", "parts"]:
+        if entry_name in data:
+            for app in list(data[entry_name].keys()):
+                data[entry_name][app] = _remove_custom_data_from_dict(
+                    data[entry_name][app])
+    return data

snapcraft_legacy/project/_project_info.py

@@ -20,14 +20,17 @@
 from snapcraft_legacy import yaml_utils
 
 from . import _schema
-
+from snapcraft.utils import (
+    remove_custom_data,
+)
 
 class ProjectInfo:
     """Information gained from the snap's snapcraft.yaml file."""
 
     def __init__(self, *, snapcraft_yaml_file_path) -> None:
         self.snapcraft_yaml_file_path = snapcraft_yaml_file_path
-        self.__raw_snapcraft = yaml_utils.load_yaml_file(snapcraft_yaml_file_path)
+        self.__raw_snapcraft = remove_custom_data(
+            yaml_utils.load_yaml_file(snapcraft_yaml_file_path))
 
         try:
             self.name = self.__raw_snapcraft["name"]