RemoveImportsVisitor crashes when parsing Literal["r+"]

[Hnasar]

https://peps.python.org/pep-0586/#shortening-unions-of-literals

The parser is trying to see if the string "r+" refers to some stringified-type and fails to parse it as an expression, but it should just take "r+" as a literal string.

This crashes in both the python and rust/native parser as of libcst 0.4.9

Repro:

# foo.py
from typing import Literal
x: Literal["r+"] = "r+"

# mods/mymod.py
import libcst as cst
from libcst.codemod import VisitorBasedCodemodCommand
from libcst.codemod.visitors import RemoveImportsVisitor


class CrashMod(VisitorBasedCodemodCommand):
    DESCRIPTION: str = "Crash on literal"

    def leave_AnnAssign(
        self, original_node: cst.AnnAssign, updated_node: cst.AnnAssign,
    ) -> cst.AnnAssign:
        RemoveImportsVisitor.remove_unused_import(self.context, "typing")
        return updated_node

# .libcst.codemod.yaml
generated_code_marker: '@generated'
formatter: ['black', '-']
blacklist_patterns: []
modules:
- 'mods'
repo_root: '.'

Output:

python -m libcst.tool codemod mymod.CrashMod foo.py
...
  File "libcst/codemod/visitors/_gather_string_annotation_names.py", line 65, in visit_SimpleString
    self.handle_any_string(node)
  File "libcst/codemod/visitors/_gather_string_annotation_names.py", line 74, in handle_any_string
    mod = cst.parse_module(value)
  File "libcst/_parser/entrypoints.py", line 109, in parse_module
    result = _parse(
  File "libcst/_parser/entrypoints.py", line 56, in _parse
    return _pure_python_parse(
  File "libcst/_parser/entrypoints.py", line 89, in _pure_python_parse
    result = parser.parse()
  File "libcst/_parser/base_parser.py", line 110, in parse
    self._add_token(token)
  File "libcst/_parser/base_parser.py", line 186, in _add_token
    raise ParserSyntaxError(
libcst._exceptions.ParserSyntaxError: Syntax Error @ 1:3.
Incomplete input. Unexpectedly encountered '\n'.

r+
  ^

[Hnasar]

This also fails when parsing Literal["1d", "1w"]

  File foo line 635, in transform_module
    mod = RemoveImportsVisitor(self.context).transform_module(mod)
  File "venv3.10/lib/python3.10/site-packages/libcst/codemod/_codemod.py", line 108, in transform_module
    return self.transform_module_impl(tree_with_metadata)
  File "venv3.10/lib/python3.10/site-packages/libcst/codemod/_visitor.py", line 32, in transform_module_impl
    return tree.visit(self)
  File "venv3.10/lib/python3.10/site-packages/libcst/_nodes/module.py", line 90, in visit
    result = super(Module, self).visit(visitor)
  ...
  File "venv3.10/lib/python3.10/site-packages/libcst/_nodes/base.py", line 219, in visit
    should_visit_children = visitor.on_visit(self)
  File "venv3.10/lib/python3.10/site-packages/libcst/matchers/_visitors.py", line 720, in on_visit
    return CSTVisitor.on_visit(self, node)
  File "venv3.10/lib/python3.10/site-packages/libcst/_visitors.py", line 123, in on_visit
    retval = visit_func(node)
  File "venv3.10/lib/python3.10/site-packages/libcst/codemod/visitors/_gather_unused_imports.py", line 71, in visit_Module
    node.visit(annotation_visitor)
  File "venv3.10/lib/python3.10/site-packages/libcst/_nodes/module.py", line 90, in visit
    result = super(Module, self).visit(visitor)
  ...
  File "venv3.10/lib/python3.10/site-packages/libcst/_nodes/base.py", line 228, in visit
    _CSTNodeSelfT, self._visit_and_replace_children(visitor)
  File "venv3.10/lib/python3.10/site-packages/libcst/_nodes/expression.py", line 1460, in _visit_and_replace_children
    value=visit_required(self, "value", self.value, visitor),
  File "venv3.10/lib/python3.10/site-packages/libcst/_nodes/internal.py", line 81, in visit_required
    result = node.visit(visitor)
  File "venv3.10/lib/python3.10/site-packages/libcst/_nodes/base.py", line 219, in visit
    should_visit_children = visitor.on_visit(self)
  File "venv3.10/lib/python3.10/site-packages/libcst/matchers/_visitors.py", line 720, in on_visit
    return CSTVisitor.on_visit(self, node)
  File "venv3.10/lib/python3.10/site-packages/libcst/_visitors.py", line 123, in on_visit
    retval = visit_func(node)
  File "venv3.10/lib/python3.10/site-packages/libcst/codemod/visitors/_gather_string_annotation_names.py", line 65, in visit_SimpleString
    self.handle_any_string(node)
  File "venv3.10/lib/python3.10/site-packages/libcst/codemod/visitors/_gather_string_annotation_names.py", line 74, in handle_any_string
    mod = cst.parse_module(value)
  File "venv3.10/lib/python3.10/site-packages/libcst/_parser/entrypoints.py", line 109, in parse_module
    result = _parse(
  File "venv3.10/lib/python3.10/site-packages/libcst/_parser/entrypoints.py", line 55, in _parse
    return parse(source_str)
libcst._exceptions.ParserSyntaxError: Syntax Error @ 1:1.
parser error: error at 1:2: expected one of !=, %, &, (, *, **, +, ,, -, ., /, //, ;, <, <<, <=, ==, >, >=, >>, @, NEWLINE, [, ^, and, if, in, is, not, or, |

1d
^```