Allow field conditions without then clause

Ref. #95

doc/Language-Reference.md

@@ -83,6 +83,7 @@ A message type is a collection components. Additional then clauses allow to defi
 *message_definition* ::= __message__ [ *null_component* ] *component* { *component* } __end message__ | __null message__
 
 *component* ::= *component_name* __:__ *component_type*
+                   [__if__ *condition*]
                    { *then_clause* } __;__
 
 *null_component* ::= __null__
@@ -108,7 +109,7 @@ A message type is a collection components. Additional then clauses allow to defi
 
 #### Static Semantics
 
-A message type specifies the message format of a protocol. Each component corresponds to one field in a message. A then clause of a component allows to define which field follows. If no then clause is given, it is assumed that always the next component of the message follows. If no further component follows, it is assumed that the message ends with this field. The end of a message can also be denoted explicitly by adding a then clause to __null__. Optionally a then clause can contain a condition under which the corresponding field follows and aspects which allow to define the length of the next field and the location of its first bit. The condition can refer to previous fields (including the component containing the then clause). If required, a null component can be used to specify the length of the first field in the message. An empty message can be represented by a null message.
+A message type specifies the message format of a protocol. Each component corresponds to one field in a message. A then clause of a component allows to define which field follows. If no then clause is given, it is assumed that always the next component of the message follows. If no further component follows, it is assumed that the message ends with this field. The end of a message can also be denoted explicitly by adding a then clause to __null__. Optionally a then clause can contain a condition under which the corresponding field follows and aspects which allow to define the length of the next field and the location of its first bit. The condition can refer to previous fields (including the component containing the then clause). A condition can also be added to a component. A component condition is equivalent to adding a condition to all incoming then clauses. If a component condition as well as a condition at an incoming then clause exists, both conditions are combined by a logical conjunction. If required, a null component can be used to specify the length of the first field in the message. An empty message can be represented by a null message.
 
 #### Example
 

rflx/model/message.py

@@ -3,7 +3,7 @@
 from abc import abstractmethod
 from collections import defaultdict
 from copy import copy
-from dataclasses import dataclass
+from dataclasses import dataclass, field as dataclass_field
 from typing import Any, Dict, List, Mapping, Optional, Sequence, Set, Tuple
 
 import rflx.typing_ as rty
@@ -52,7 +52,7 @@ class Link(Base):
     condition: expr.Expr = expr.TRUE
     length: expr.Expr = expr.UNDEFINED
     first: expr.Expr = expr.UNDEFINED
-    location: Optional[Location] = None
+    location: Optional[Location] = dataclass_field(default=None, repr=False)
 
     def __str__(self) -> str:
         condition = indent_next(

rflx/specification/ast.py

@@ -41,11 +41,16 @@ def __eq__(self, other: object) -> bool:
 
 class Component(SyntaxTree):
     def __init__(
-        self, name: StrID = None, type_name: StrID = None, thens: List[Then] = None
+        self,
+        name: StrID = None,
+        type_name: StrID = None,
+        thens: List[Then] = None,
+        condition: Expr = TRUE,
     ) -> None:
         self.name = ID(name) if name else None
         self.type_name = ID(type_name) if type_name else None
         self.thens = thens or []
+        self.condition = condition
 
 
 @dataclass

rflx/specification/grammar.py

@@ -442,11 +442,12 @@ def message_type_definition() -> Token:
         - unqualified_identifier()
         + Literal(":")
         - qualified_identifier()
+        - Optional(if_condition(restricted=True), TRUE)
         - then_list
         - semicolon()
     )
     component_item.setParseAction(
-        lambda t: Component(t[0], t[2], t[3]) if len(t) >= 4 else Component(t[0], t[2])
+        lambda t: Component(t[0], t[2], t[4], t[3]) if len(t) >= 5 else Component(t[0], t[2])
     )
     component_item.setName("Component")
     null_component_item = Keyword("null") - then - semicolon()

rflx/specification/parser.py

@@ -5,6 +5,7 @@
 
 from pyparsing import ParseException, ParseFatalException
 
+import rflx.expression as expr
 from rflx.error import (
     RecordFluxError,
     Severity,
@@ -14,7 +15,6 @@
     pop_source,
     push_source,
 )
-from rflx.expression import UNDEFINED
 from rflx.identifier import ID
 from rflx.model import (
     BUILTIN_TYPES,
@@ -267,6 +267,8 @@ def create_message(
     skip_verification: bool,
     cache: Cache,
 ) -> Message:
+    # pylint: disable=too-many-locals
+
     components = list(message.components)
 
     if components and components[0].name:
@@ -296,7 +298,7 @@ def create_message(
                         then.first.location,
                     )
                     for then in component.thens
-                    if then.first != UNDEFINED
+                    if then.first != expr.UNDEFINED
                 ]
             )
 
@@ -307,6 +309,15 @@ def create_message(
             target_node = Field(name) if name else FINAL
             structure.append(Link(source_node, target_node))
 
+        if component.condition != expr.TRUE:
+            for l in structure:
+                if l.target.identifier == component.name:
+                    l.condition = (
+                        expr.And(component.condition, l.condition, location=l.condition.location)
+                        if l.condition != expr.TRUE
+                        else component.condition
+                    )
+
         for then in component.thens:
             target_node = Field(then.name) if then.name else FINAL
             if then.name and target_node not in field_types.keys():

tests/unit/specification/parser_test.py

@@ -9,10 +9,13 @@
 from rflx import expression as expr, model
 from rflx.error import Location, RecordFluxError, Severity, Subsystem, fail
 from rflx.identifier import ID
+from rflx.model import FINAL, INITIAL, Field, Link, Message, ModularInteger
 from rflx.specification import ast, cache, parser
 from tests.const import EX_SPEC_DIR, SPEC_DIR
 from tests.data import models
 
+T = ModularInteger("Test::T", expr.Number(256))
+
 
 def assert_specifications_files(
     filenames: Sequence[str], specifications: Mapping[str, ast.Specification]
@@ -1120,3 +1123,67 @@ def test_create_model_checksum() -> None:
             )
         ],
     }
+
+
+@pytest.mark.parametrize(
+    "spec",
+    [
+        """
+               type M is
+                  message
+                     A : T
+                        then B
+                           if A < 100;
+                     B : T
+                        if A > 10;
+                  end message;
+            """,
+        """
+               type M is
+                  message
+                     A : T;
+                     B : T
+                        if A > 10 and A < 100;
+                  end message;
+            """,
+        """
+               type M is
+                  message
+                     A : T
+                        then B
+                           if A > 10 and A < 100;
+                     B : T;
+                  end message;
+            """,
+    ],
+)
+def test_message_field_condition(spec: str) -> None:
+    assert_messages_string(
+        f"""
+            package Test is
+
+               type T is mod 256;
+
+               {spec}
+
+            end Test;
+        """,
+        [
+            Message(
+                "Test::M",
+                [
+                    Link(INITIAL, Field("A")),
+                    Link(
+                        Field("A"),
+                        Field("B"),
+                        condition=expr.And(
+                            expr.Greater(expr.Variable("A"), expr.Number(10)),
+                            expr.Less(expr.Variable("A"), expr.Number(100)),
+                        ),
+                    ),
+                    Link(Field("B"), FINAL),
+                ],
+                {Field("A"): T, Field("B"): T},
+            ),
+        ],
+    )