Add check for unsupported exponentiations

Ref. #320

rflx/model.py

@@ -667,6 +667,7 @@ def prefixed_expression(expression: Expr) -> Expr:
 
         return self.copy(structure=structure, types=types)
 
+    # pylint: disable=too-many-branches
     def __verify(self) -> None:
         type_fields = self.__types.keys() | {INITIAL, FINAL}
         structure_fields = {l.source for l in self.structure} | {l.target for l in self.structure}
@@ -756,6 +757,28 @@ def __verify(self) -> None:
                     [("duplicate link", Subsystem.MODEL, Severity.INFO, l.location,) for l in links]
                 )
 
+        for l in self.structure:
+            exponentiations = And(l.condition, l.first, l.length).findall(
+                lambda x: isinstance(x, Pow)
+            )
+            for e in exponentiations:
+                assert isinstance(e, Pow)
+                variables = e.right.findall(lambda x: isinstance(x, Variable))
+                if variables:
+                    self.error.append(
+                        f'unsupported expression in "{self.identifier}"',
+                        Subsystem.MODEL,
+                        Severity.ERROR,
+                        e.location,
+                    )
+                    for v in variables:
+                        self.error.append(
+                            f'variable "{v}" in exponent',
+                            Subsystem.MODEL,
+                            Severity.INFO,
+                            v.location,
+                        )
+
     def __verify_conditions(self) -> None:
         literals = qualified_literals(self.types, self.package)
         variables = {f.identifier for f in self.fields}

tests/test_model.py

@@ -487,6 +487,35 @@ def test_message_multiple_duplicate_links() -> None:
     )
 
 
+def test_message_unsupported_expression() -> None:
+    x = Field("X")
+
+    structure = [
+        Link(INITIAL, x),
+        Link(
+            x,
+            FINAL,
+            condition=LessEqual(
+                Pow(
+                    Number(2),
+                    Add(Variable("X", location=Location((10, 23))), Number(1)),
+                    location=Location((10, 19)),
+                ),
+                Number(1024),
+            ),
+        ),
+    ]
+
+    types = {x: MODULAR_INTEGER}
+
+    assert_message_model_error(
+        structure,
+        types,
+        '^<stdin>:10:19: model: error: unsupported expression in "P.M"\n'
+        '<stdin>:10:23: model: info: variable "X" in exponent',
+    )
+
+
 def test_message_unreachable_field() -> None:
     structure = [
         Link(INITIAL, Field("X")),