Change representation of null messages

Ref. #643

CHANGELOG.md

@@ -16,8 +16,14 @@ CLI:
 
 ### Changed
 
+Specification:
+
 - Syntax for defining initial and final states of session (#700)
 
+Model:
+
+- Change representation of null messages (#643)
+
 ### Removed
 
 Specification:

rflx/graph.py

@@ -1,14 +1,13 @@
 import logging
 import re
-from copy import copy
 from pathlib import Path
 from typing import Sequence
 
 from pydotplus import Dot, Edge, Node
 
 from rflx.expression import TRUE, UNDEFINED
 from rflx.identifier import ID
-from rflx.model import FINAL, FINAL_STATE, INITIAL, AbstractSession, Link, Message
+from rflx.model import FINAL_STATE, AbstractSession, Link, Message
 
 log = logging.getLogger(__name__)
 
@@ -54,19 +53,13 @@ def _edge_label(link: Link) -> str:
             first=str(link.first) if link.first != UNDEFINED else "⋆",
         )
 
-    msg = copy(message)
-    if not msg.structure:
-        # https://github.com/Componolit/RecordFlux/issues/643
-        # pylint: disable-next = protected-access
-        msg._structure = [Link(INITIAL, FINAL)]
-
-    result = _graph_with_defaults(msg.full_name)
+    result = _graph_with_defaults(message.full_name)
     result.add_node(
         Node(name="Initial", fillcolor="#ffffff", shape="circle", width="0.5", label="")
     )
-    for f in msg.fields:
+    for f in message.fields:
         result.add_node(Node(name=f.name))
-    for i, l in enumerate(msg.structure):
+    for i, l in enumerate(message.structure):
         intermediate_node = f"intermediate_{i}"
         result.add_node(
             Node(

rflx/model/message.py

@@ -128,6 +128,9 @@ def __init__(
 
         assert len(self.identifier.parts) > 1, "type identifier must contain package"
 
+        if not structure:
+            structure = [Link(INITIAL, FINAL)]
+
         self._structure = sorted(structure)
         self._types = types
         self._paths_cache: Dict[Field, Set[Tuple[Link, ...]]] = {}
@@ -142,7 +145,7 @@ def __init__(
         self._byte_order = {}
 
         try:
-            if not state and (structure or types):
+            if not state and not self.is_null:
                 self._state.has_unreachable = self._validate()
                 self._normalize()
                 fields = self._compute_topological_sorting(self._state.has_unreachable)
@@ -184,7 +187,7 @@ def __repr__(self) -> str:
         return verbose_repr(self, ["identifier", "structure", "types", "checksums", "byte_order"])
 
     def __str__(self) -> str:
-        if not self.structure or not self.types:
+        if self.is_null:
             return f"type {self.name} is null message"
 
         parameters = "; ".join(
@@ -220,6 +223,10 @@ def __str__(self) -> str:
 
         return f"type {self.name}{parameters} is\n   message\n{indent(fields, 6)}\n   end message"
 
+    @property
+    def is_null(self) -> bool:
+        return self._structure == [Link(INITIAL, FINAL)] and not self._types
+
     @property
     def direct_dependencies(self) -> List[mty.Type]:
         return [*self._types.values(), self]
@@ -839,7 +846,7 @@ def __init__(
         self.error.propagate()
 
     def verify(self) -> None:
-        if self.structure or self.types:
+        if not self.is_null:
             self._verify_expression_types()
             self._verify_expressions()
             self._verify_checksums()
@@ -910,7 +917,7 @@ def type_(self) -> rty.Message:
                 )
                 for p in self.paths(FINAL)
             }
-            if self.structure
+            if not self.is_null
             else set(),
             {f.identifier: t.type_ for f, t in self._state.parameter_types.items()},
             {f.identifier: t.type_ for f, t in self._state.field_types.items()},
@@ -1005,7 +1012,7 @@ def typed_variable(expression: expr.Expr) -> expr.Expr:
                     self.location,
                 )
         else:
-            if not self.structure:
+            if self.is_null:
                 return expr.Number(0)
 
             fields = list(self.fields)
@@ -1164,7 +1171,7 @@ def remove_variable_prefix(expression: expr.Expr) -> expr.Expr:
         )
 
     def max_size(self) -> expr.Number:
-        if not self.structure:
+        if self.is_null:
             return expr.Number(0)
 
         if self.has_implicit_size:
@@ -1183,7 +1190,7 @@ def max_size(self) -> expr.Number:
         return max_size
 
     def max_field_sizes(self) -> Dict[Field, expr.Number]:
-        if not self.structure:
+        if self.is_null:
             return {}
 
         if self.has_implicit_size:

rflx/model/type_.py

@@ -603,7 +603,7 @@ def __init__(self, identifier: StrID, element_type: Type, location: Location = N
                 location,
             )
 
-            if not element_type.structure:
+            if element_type.is_null:
                 self.error.extend(
                     [
                         error,

rflx/pyrflx/typevalue.py

@@ -741,9 +741,7 @@ def _valid_refinement_condition(self, refinement: "RefinementValue") -> bool:
 
     def _next_link(self, source_field_name: str) -> ty.Optional[Link]:
         field = Field(source_field_name)
-        if field == FINAL or not self._type.structure:
-            # structure is empty in case of NULL message
-            # https://github.com/Componolit/RecordFlux/issues/643
+        if field == FINAL:
             return None
         for link in self._type.outgoing(field):
             if self._simplified(link.condition) == TRUE:
@@ -758,10 +756,6 @@ def _next_field(self, field_name: str, append_to_path: bool = False) -> str:
         if append_to_path and next_link is not None:
             self._path.append(next_link)
 
-        if next_link is None and field_name == INITIAL.name:
-            # the INITIAL field has no outgoing links in case of NULL message
-            # https://github.com/Componolit/RecordFlux/issues/643
-            return FINAL.name
         return next_link.target.name if next_link is not None else ""
 
     def _prev_field(self, fld: str) -> str: