ei-scanner: Expose interface_arg, and also provide interface_arg_for

To make this practical to use in a template, we want relations in both
directions. And at least for consistency with other things, these fields
should contain the `Argument` instead of just its name string.

So we need to do this after are the arguments in the message have been
initially parsed. Adding these fields when parsing the request/event
close tag seems to work well enough.

Co-authored-by: Peter Hutterer <peter.hutterer@who-t.net>

proto/ei-scanner

@@ -17,7 +17,7 @@ Opcodes for events and request are assigned in order as they
 appear in the XML file.
 """
 
-from typing import Any, List, Optional, Tuple, Union
+from typing import Any, Dict, List, Optional, Tuple, Union
 from pathlib import Path
 from textwrap import dedent
 
@@ -72,6 +72,16 @@ class Argument:
     summary: str = attr.ib()
     enum: Optional["Enum"] = attr.ib()
     interface: Optional["Interface"] = attr.ib()
+    interface_arg: Optional["Argument"] = attr.ib(default=None)
+    """
+    For an argument with "interface_arg", this field points to the argument that
+    contains the interface name.
+    """
+    interface_arg_for: Optional["Argument"] = attr.ib(default=None)
+    """
+    For an argument referenced by another argument through "interface_name", this field
+    points to the other argument that references this argument.
+    """
 
     @property
     def signature(self) -> str:
@@ -165,6 +175,12 @@ class Message:
     def camel_name(self) -> str:
         return snake2camel(self.name)
 
+    def find_argument(self, name: str) -> Optional[Argument]:
+        for a in self.arguments:
+            if a.name == name:
+                return a
+        return None
+
 
 @attr.s
 class Request(Message):
@@ -447,6 +463,8 @@ class ProtocolParser(xml.sax.handler.ContentHandler):
     current_interface: Optional[Interface] = attr.ib(init=False, default=None)
     current_message: Optional[Union[Message, Enum]] = attr.ib(init=False, default=None)
     current_description: Optional[Description] = attr.ib(init=False, default=None)
+    # A dict of arg name to interface_arg name mappings
+    current_interface_arg_names: Dict[str, str] = attr.ib(init=False, default=attr.Factory(dict))  # type: ignore
 
     _run_counter: int = attr.ib(init=False, default=0, repr=False)
 
@@ -658,6 +676,13 @@ class ProtocolParser(xml.sax.handler.ContentHandler):
                 interface = self.interface_by_name(interface_name)
             else:
                 interface = None
+
+            # interface_arg is set to the name of some other arg that specifies the actual
+            # interface name for this argument
+            interface_arg_name = attrs.get("interface_arg", None)
+            if interface_arg_name is not None:
+                self.current_interface_arg_names[name] = interface_arg_name
+
             enum_name = attrs.get("enum", None)
             enum = None
             if enum_name is not None:
@@ -734,6 +759,21 @@ class ProtocolParser(xml.sax.handler.ContentHandler):
         if self._run_counter <= 2:
             return
 
+        # Populate `interface_arg` and `interface_arg_for`, now we have all arguments
+        if name in ["request", "event"]:
+            assert isinstance(self.current_message, Message)
+            # obj is the argument of type object that the interface applies to
+            # iname is the argument of type "interface_name" that specifies the interface
+            for obj, iname in self.current_interface_arg_names.items():
+                obj_arg = self.current_message.find_argument(obj)
+                iname_arg = self.current_message.find_argument(iname)
+
+                assert obj_arg is not None
+                assert iname_arg is not None
+
+                obj_arg.interface_arg = iname_arg
+                iname_arg.interface_arg_for = obj_arg
+            self.current_interface_arg_names = {}
         if name == "request":
             assert isinstance(self.current_message, Request)
             self.current_message = None

test/test_scanner.py

@@ -45,6 +45,19 @@ class TestScanner:
         assert "connection" in [i.plainname for i in protocol.interfaces]
         assert "button" in [i.plainname for i in protocol.interfaces]
 
+    @pytest.mark.parametrize("component", ("ei",))
+    def test_interface_arg(self, protocol: Protocol):
+        intf = next((i for i in protocol.interfaces if i.name == "ei_device"))
+        event = next((e for e in intf.events if e.name == "interface"))
+
+        obj, interface_name, version = event.arguments
+        assert obj.interface_arg == interface_name
+        assert obj.interface_arg_for is None
+        assert interface_name.interface_arg_for == obj
+        assert interface_name.interface_arg is None
+        assert version.interface_arg is None
+        assert version.interface_arg_for is None
+
     @pytest.mark.parametrize("method", ("yamlfile", "jsonfile", "string"))
     def test_cli_extra_data(self, tmp_path, method):
         result_path = tmp_path / "result"