nac3-spec/toy-impl/top_level.py

import ast
from type_def import *
from helper import *


def parse_type(ctx: Context, ty):
    if ty is None:
        return None, set()
    elif isinstance(ty, ast.Name):
        # we should support string either, but no need for toy implementation
        if ty.id in ctx.types:
            return ctx.types[ty.id], set()
        elif ty.id in ctx.variables:
            return ctx.variables[ty.id], {ty.id}
        else:
            raise CustomError(f"Unbounded Type {ty.id}")
    elif isinstance(ty, ast.Subscript):
        if isinstance(ty.value, ast.Name):
            generic = ty.value.id
        else:
            raise CustomError(f"Unknown Generic Type {ty.value}")
        if not isinstance(ty.slice, ast.Name) and not isinstance(ty.slice, ast.Tuple) \
                and not isinstance(ty.slice, ast.Subscript):
            raise CustomError(f"Generic Type of the form {ty.slice} is not supported")
        if generic == 'tuple':
            if not isinstance(ty.slice, ast.Tuple):
                raise CustomError(f"Generic Type of the form {ty} is not supported")
            param = []
            var = set()
            for t in ty.slice.elts:
                p, v = parse_type(ctx, t)
                param.append(p)
                var |= v
            return TupleType(param), var
        elif generic == 'list':
            param, var = parse_type(ctx, ty.slice)
            return ListType(param), var
        elif generic == 'virtual':
            param, var = parse_type(ctx, ty.slice)
            if not isinstance(param, ClassType):
                raise CustomError(f"Parameter of virtual must be a class instead of {param}")
            return VirtualClassType(param), var
        else:
            raise CustomError(f"Unknown Generic Type {ty.value}")
    else:
        raise CustomError(f"Unrecognized Type {ty}")


def parse_function(ctx: Context, base, fn: ast.FunctionDef):
    args = []
    var = set()
    for arg in fn.args.args:
        name = arg.arg
        ty, v = parse_type(ctx, arg.annotation)
        var |= v
        if name == 'self' and ty is None and base is not None:
            ty = SelfType()
        args.append(ty)
    if isinstance(fn.returns, ast.Name) and fn.returns.id == 'self'\
            and base is not None:
        result, v = SelfType(), set()
    else:
        result, v = parse_type(ctx, fn.returns)
    if len(v - var) > 0:
        raise CustomError(f"Unbounded variable in return type of {fn.name}")
    return args, result, var


def parse_class(ctx, c: ast.ClassDef):
    node = ctx.types[c.name]
    functions = []

    for base in c.bases:
        if not isinstance(base, ast.Name):
            raise CustomError(f"Base class of the form {base} is not supported")
        name = base.id
        if name not in ctx.types:
            raise CustomError(f"Unbounded base class name {base}")
        if not isinstance(ctx.types[name], ClassType):
            raise CustomError(f"Base class must be a class instead of {base}")
        node.parents.append(ctx.types[name])

    for stmt in c.body:
        if isinstance(stmt, ast.AnnAssign):
            if not isinstance(stmt.target, ast.Name):
                raise CustomError(f"Assignment of the form {stmt.target} is not supported")
            field = stmt.target.id
            if field in node.fields:
                raise CustomError(f"Duplicated fields {field} in {c.name}")
            ty, var = parse_type(ctx, stmt.annotation)
            if len(var) > 0:
                raise CustomError(f"Type variable is not allowed in class fields")
            if ty == None:
                raise CustomError(f"{field} of {c.name} is not annotated")
            node.fields[field] = ty
        elif isinstance(stmt, ast.FunctionDef):
            name = stmt.name
            if name in node.methods:
                raise CustomError(f"Duplicated method {name} in {c.name}")
            args, result, var = parse_function(ctx, node, stmt)
            node.methods[name] = (args, result, var)
            functions.append((c.name, name, stmt))
        else:
            raise CustomError(f"{stmt} is not supported")
    return functions


def parse_type_var(ctx: Context, node):
    if isinstance(node, ast.Assign):
        if not isinstance(node.value, ast.Call) or\
                not isinstance(node.value.func, ast.Name) or\
                node.value.func.id != 'TypeVar':
            return
        if not len(node.targets) == 1 or\
                not isinstance(node.targets[0], ast.Name):
            raise CustomError(
                'complicated variable assignment is not allowed',
                node)
        if len(node.value.args) == 0 or\
                not isinstance(node.value.args[0], ast.Constant) or\
                not isinstance(node.value.args[0].value, str):
            raise CustomError('call to TypeVar must at least have a name',
                              node.value)
        name = node.targets[0].id
        if name in ctx.variables:
            raise CustomError('redefining type variable is not allowed', node)
        constraints = []
        for v in node.value.args[1:]:
            value, var = parse_type(ctx, v)
            if len(var) > 0:
                raise CustomError(
                    'constraints cannot contain type variables',
                    node)
            constraints.append(value)
        ctx.variables[name] = TypeVariable(node.value.args[0].value, constraints)


def parse_top_level(ctx: Context, module: ast.Module):
    to_be_processed = []
    assignments = []
    # first pass, obtain all type names
    for element in module.body:
        if isinstance(element, ast.ClassDef):
            name = element.name
            if name in ctx.types or name in ctx.variables:
                raise CustomError(f"Duplicated class name: {name}")
            ctx.types[name] = ClassType(name)
            to_be_processed.append(element)
        elif isinstance(element, ast.FunctionDef):
            to_be_processed.append(element)
        elif isinstance(element, ast.Assign):
            assignments.append(element)

    # second pass, obtain all type variables
    for node in assignments:
        parse_type_var(ctx, node)

    # third pass, obtain all function types
    function_stmts = []
    for element in to_be_processed:
        if isinstance(element, ast.ClassDef):
            function_stmts += parse_class(ctx, element)
        elif isinstance(element, ast.FunctionDef):
            name = element.name
            if name in ctx.functions:
                raise CustomError(f"Duplicated function name {name}")
            if name in ctx.types:
                raise CustomError(f"Function name {name} clashed with type name")
            args, result, var = parse_function(ctx, None, element)
            ctx.functions[name] = (args, result, var)
            function_stmts.append((None, name, element))

    return ctx, function_stmts