edit_validation.py

"""A narrow editing contract, not a security sandbox for hostile Python."""

import ast
import builtins


BUILTINS = {name: getattr(builtins, name) for name in (
    "all", "any", "bool", "dict", "enumerate", "float", "int", "len", "list",
    "max", "min", "range", "reversed", "set", "sorted", "str", "sum", "tuple",
    "zip", "Exception", "RuntimeError", "ValueError", "AssertionError")}
METHODS = frozenset({
    "get_child_instance", "get_child_instances", "get_leaf_children", "get_term",
    "get_terms", "get_net", "get_nets", "get_upper_net", "get_lower_net",
    "get_bits", "get_bit", "get_name", "get_model_name", "get_direction",
    "is_input", "is_output", "is_inout", "is_leaf", "is_sequential",
    "create_net", "create_child_instance", "connect_upper_net", "disconnect",
    "delete", "rename", "get", "items", "keys", "values", "append", "extend",
    "add", "update", "pop", "copy", "index", "count",
})


def validate_script(source):
    """Permit pure helper definitions and calls on the provided candidate only."""
    if not isinstance(source, str) or len(source.encode()) > 1024 * 1024:
        raise ValueError("Edit script must be text no larger than 1 MiB")
    tree = ast.parse(source, filename="candidate-edit.py")
    functions = {node.name for node in tree.body if isinstance(node, ast.FunctionDef)}
    edits = [node for node in tree.body if isinstance(node, ast.FunctionDef) and node.name == "edit"]
    if (len(edits) != 1 or len(edits[0].args.args) != 1 or edits[0].args.posonlyargs
            or edits[0].args.kwonlyargs or edits[0].args.vararg or edits[0].args.kwarg):
        raise ValueError("Define exactly one edit(top) function")
    for node in tree.body:
        if isinstance(node, ast.Expr) and isinstance(node.value, ast.Constant) and isinstance(node.value.value, str):
            continue
        if not isinstance(node, ast.FunctionDef):
            raise ValueError("Only function definitions are allowed at module level; no imports/load/reset/export")
    forbidden = (ast.Import, ast.ImportFrom, ast.Global, ast.Nonlocal, ast.ClassDef,
                 ast.AsyncFunctionDef, ast.Await, ast.Yield, ast.YieldFrom, ast.With, ast.AsyncWith)
    for node in ast.walk(tree):
        if isinstance(node, forbidden):
            raise ValueError(f"Unsupported editing construct: {type(node).__name__}")
        if isinstance(node, ast.FunctionDef):
            if node.decorator_list or node.args.defaults or node.args.kw_defaults or node.returns:
                raise ValueError("Edit helpers cannot have decorators, defaults or return annotations")
        if isinstance(node, ast.arg) and (node.annotation or (node.arg.startswith("_") and node.arg != "_")):
            raise ValueError("Private names and annotations are not allowed")
        if isinstance(node, ast.Name) and node.id.startswith("_") and node.id != "_":
            raise ValueError("Private names are not allowed")
        if isinstance(node, ast.Attribute) and node.attr not in METHODS:
            raise ValueError(f"Unsupported editing attribute: {node.attr}")
        if isinstance(node, ast.Call):
            if isinstance(node.func, ast.Name) and node.func.id not in functions | BUILTINS.keys():
                raise ValueError(f"Unsupported editing call: {node.func.id}")
            if not isinstance(node.func, (ast.Name, ast.Attribute)):
                raise ValueError("Indirect editing calls are not allowed")
    return compile(tree, "candidate-edit.py", "exec", optimize=0)


def editing_function(source):
    code = validate_script(source)
    namespace = {"__builtins__": dict(BUILTINS)}
    exec(code, namespace)
    return namespace["edit"]