better variable cycle detection

src/ytdl_sub/script/functions/array_functions.py

@@ -47,6 +47,8 @@ class ArrayFunctions:
         """
         return Array(list(reversed(array.value)))
 
+    # pylint: disable=unused-argument
+
     @staticmethod
     def array_apply(array: Array, lambda_function: Lambda) -> Array:
         """
@@ -63,3 +65,5 @@ class ArrayFunctions:
         return ResolvedArray(
             [ResolvedArray([Integer(idx), val]) for idx, val in enumerate(array.value)]
         )
+
+    # pylint: enable=unused-argument

src/ytdl_sub/script/script.py

@@ -6,8 +6,11 @@ from ytdl_sub.script.parser import parse
 from ytdl_sub.script.types.resolvable import Resolvable
 from ytdl_sub.script.types.syntax_tree import SyntaxTree
 from ytdl_sub.script.types.variable import Variable
+from ytdl_sub.script.utils.exceptions import UNREACHABLE
 from ytdl_sub.script.utils.exceptions import CycleDetected
 
+# pylint: disable=missing-raises-doc
+
 
 class Script:
     """
@@ -28,6 +31,32 @@ class Script:
         """
         return function_key[1:]
 
+    def _traverse_variable_dependencies(
+        self,
+        variable_name: str,
+        variable_dependency: SyntaxTree,
+        deps: List[str],
+    ) -> None:
+        for dep in variable_dependency.variables:
+            if variable_name in deps + [dep.name]:
+                cycle_deps = [variable_name] + deps + [dep.name]
+                cycle_deps_str = " -> ".join(cycle_deps)
+                raise CycleDetected(f"Cycle detected within these variables: {cycle_deps_str}")
+
+            self._traverse_variable_dependencies(
+                variable_name=variable_name,
+                variable_dependency=self._variables[dep.name],
+                deps=deps + [dep.name],
+            )
+
+    def _ensure_no_variable_cycles(self):
+        for variable_name, variable_definition in self._variables.items():
+            self._traverse_variable_dependencies(
+                variable_name=variable_name,
+                variable_dependency=variable_definition,
+                deps=[],
+            )
+
     def _traverse_custom_function_dependencies(
         self,
         custom_function_name: str,
@@ -38,7 +67,9 @@ class Script:
             if custom_function_name in deps + [dep.name]:
                 cycle_deps = [custom_function_name] + deps + [dep.name]
                 cycle_deps_str = " -> ".join([f"%{name}" for name in cycle_deps])
-                raise CycleDetected(f"Custom functions contain a cycle: {cycle_deps_str}")
+                raise CycleDetected(
+                    f"Cycle detected within these custom functions: {cycle_deps_str}"
+                )
 
             self._traverse_custom_function_dependencies(
                 custom_function_name=custom_function_name,
@@ -72,6 +103,7 @@ class Script:
         }
 
         self._ensure_no_custom_function_cycles()
+        self._ensure_no_variable_cycles()
 
     def resolve(
         self, pre_resolved_variables: Optional[Dict[Variable, Resolvable]] = None
@@ -109,9 +141,8 @@ class Script:
                     unresolved_variables.remove(variable)
 
             if len(unresolved_variables) == unresolved_count:
-                raise CycleDetected(
-                    f"Cycle detected within these variables: "
-                    f"{', '.join(sorted([var.name for var in unresolved_variables]))}"
-                )
+                # Implies a cycle within the variables. Should never reach
+                # since cycles are detected in __init__
+                raise UNREACHABLE
 
         return {variable.name: resolvable for variable, resolvable in resolved_variables.items()}

src/ytdl_sub/script/types/function.py

@@ -7,13 +7,10 @@ from inspect import FullArgSpec
 from typing import Callable
 from typing import Dict
 from typing import List
-from typing import Optional
-from typing import Set
 from typing import Type
 from typing import Union
 
 from ytdl_sub.script.functions import Functions
-from ytdl_sub.script.types.array import Array
 from ytdl_sub.script.types.array import ResolvedArray
 from ytdl_sub.script.types.array import UnresolvedArray
 from ytdl_sub.script.types.resolvable import Argument
@@ -30,7 +27,6 @@ from ytdl_sub.script.types.variable import Variable
 from ytdl_sub.script.types.variable_dependency import VariableDependency
 from ytdl_sub.script.utils.exception_formatters import FunctionArgumentsExceptionFormatter
 from ytdl_sub.script.utils.exceptions import UNREACHABLE
-from ytdl_sub.script.utils.exceptions import CycleDetected
 from ytdl_sub.script.utils.exceptions import FunctionDoesNotExist
 from ytdl_sub.script.utils.exceptions import FunctionRuntimeException
 from ytdl_sub.script.utils.exceptions import UserThrownRuntimeError

src/ytdl_sub/script/types/map.py

@@ -2,7 +2,6 @@ import itertools
 from dataclasses import dataclass
 from typing import Dict
 from typing import List
-from typing import Set
 
 from ytdl_sub.script.types.resolvable import AnyArgument
 from ytdl_sub.script.types.resolvable import Argument

tests/unit/script/test_script.py

@@ -1,7 +1,10 @@
+import re
+
 import pytest
 
 from ytdl_sub.script.script import Script
 from ytdl_sub.script.types.resolvable import String
+from ytdl_sub.script.utils.exceptions import CycleDetected
 from ytdl_sub.utils.exceptions import StringFormattingException
 
 
@@ -38,9 +41,15 @@ class TestSyntaxTree:
         }
 
     def test_simple_cycle(self):
-        with pytest.raises(StringFormattingException):
+        with pytest.raises(
+            CycleDetected,
+            match=re.escape("Cycle detected within these variables: " "a -> b -> a"),
+        ):
             Script({"a": "{b}", "b": "{a}"}).resolve()
 
     def test_simple_cycle_with_function(self):
-        with pytest.raises(StringFormattingException):
+        with pytest.raises(
+            CycleDetected,
+            match=re.escape("Cycle detected within these variables: " "b -> b_ -> b"),
+        ):
             Script({"b": "{%capitalize(b_)}", "b_": "{b}"}).resolve()

tests/unit/script/types/test_custom_function.py

@@ -29,7 +29,8 @@ class TestCustomFunction:
         with pytest.raises(
             CycleDetected,
             match=re.escape(
-                "Custom functions contain a cycle: %cycle_func1 -> %cycle_func0 -> %cycle_func1"
+                "Cycle detected within these custom functions: "
+                "%cycle_func1 -> %cycle_func0 -> %cycle_func1"
             ),
         ):
             Script(
@@ -44,7 +45,7 @@ class TestCustomFunction:
         with pytest.raises(
             CycleDetected,
             match=re.escape(
-                "Custom functions contain a cycle: "
+                "Cycle detected within these custom functions: "
                 "%cycle_func4 -> "
                 "%cycle_func0 -> "
                 "%cycle_func1 -> "