Source code for launch.frontend.parse_substitution

# Copyright 2019 Open Source Robotics Foundation, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Module for parsing substitutions."""

import os
import re
from typing import Text

from ament_index_python.packages import get_package_share_directory

from lark import Lark
from lark import Token
from lark import Transformer

from .expose import instantiate_substitution
from ..substitutions import TextSubstitution
from ..utilities.type_utils import NormalizedValueType
from ..utilities.type_utils import StrSomeValueType




def replace_escaped_characters(data: Text) -> Text:
    """Search escaped characters and replace them."""
    return re.sub(r'\\(.)', r'\1', data)





class ExtractSubstitution(Transformer):
    """Extract a substitution."""



    def part(self, content):
        assert len(content) == 1
        content = content[0]
        if isinstance(content, Token):
            assert content.type.endswith('_RSTRING')
            return TextSubstitution(text=replace_escaped_characters(content.value))
        return content


    single_quoted_part = part
    double_quoted_part = part



    def value(self, parts):
        if len(parts) == 1 and isinstance(parts[0], list):
            # Deal with single and double quoted templates
            return parts[0]
        return parts


    single_quoted_value = value
    double_quoted_value = value



    def arguments(self, values):
        if len(values) > 1:
            # Deal with tail recursive argument parsing
            return [*values[0], values[1]]
        return values


    single_quoted_arguments = arguments
    double_quoted_arguments = arguments



    def substitution(self, args):
        assert len(args) >= 1
        name = args[0]
        assert isinstance(name, Token)
        assert name.type == 'IDENTIFIER'
        return instantiate_substitution(name.value, *args[1:])


    single_quoted_substitution = substitution
    double_quoted_substitution = substitution



    def fragment(self, content):
        assert len(content) == 1
        content = content[0]
        if isinstance(content, Token):
            assert content.type.endswith('_STRING')
            return TextSubstitution(text=replace_escaped_characters(content.value))
        return content


    single_quoted_fragment = fragment
    double_quoted_fragment = fragment



    def template(self, fragments):
        return fragments


    single_quoted_template = template
    double_quoted_template = template





def get_grammar_path() -> str:
    return os.path.join(
        get_package_share_directory('launch'), 'frontend', 'grammar.lark')



_parser = None




def parse_substitution(string_value):
    global _parser
    if not string_value:
        # Grammar cannot deal with zero-width expressions.
        return [TextSubstitution(text=string_value)]
    if _parser is None:
        with open(get_grammar_path(), 'r') as h:
            _parser = Lark(h, start='template')
    tree = _parser.parse(string_value)
    transformer = ExtractSubstitution()
    return transformer.transform(tree)





def parse_if_substitutions(
    value: StrSomeValueType
) -> NormalizedValueType:
    """
    Parse substitutions in `value`, if there are any, and return a normalized value type.

    If `value` is a `str`, substitutions will be interpolated in it.
    If `value` is any other scalar type, it will be returned as-is.
    If `value` is a list, the two rules above will be applied to each item.
    When interpolating substitutions in a string, `TextSubstitution` instances are resolved
    and the original `str` is left.

    :raise: `ValueError` if the result cannot be parsed into a valid type.
    """
    data_types = set()

    def _parse_if(value):
        if isinstance(value, str):
            output = parse_substitution(value)
            if len(output) == 1 and isinstance(output[0], TextSubstitution):
                data_types.add(str)
                return output[0].text
            return output
        data_types.add(type(value))
        return value
    if isinstance(value, list):
        output = [_parse_if(x) for x in value]
    else:
        output = _parse_if(value)
    if len(data_types) > 1:
        raise ValueError('The result is a non-uniform list')
    return output