Mini Shell

# Copyright 2016 Grist Labs, 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.

import ast
import collections
import io
import sys
import token
import tokenize
from abc import ABCMeta
from ast import Module, expr, AST
from functools import lru_cache
from typing import (
    Callable,
    Dict,
    Iterable,
    Iterator,
    List,
    Optional,
    Tuple,
    Union,
    cast,
    Any,
    TYPE_CHECKING,
    Type,
)

if TYPE_CHECKING:  # pragma: no cover
  from .astroid_compat import NodeNG

  # Type class used to expand out the definition of AST to include fields added by this library
  # It's not actually used for anything other than type checking though!
  class EnhancedAST(AST):
    # Additional attributes set by mark_tokens
    first_token = None  # type: Token
    last_token = None  # type: Token
    lineno = 0  # type: int

  AstNode = Union[EnhancedAST, NodeNG]

  TokenInfo = tokenize.TokenInfo


def token_repr(tok_type, string):
  # type: (int, Optional[str]) -> str
  """Returns a human-friendly representation of a token with the given type and string."""
  # repr() prefixes unicode with 'u' on Python2 but not Python3; strip it out for consistency.
  return '%s:%s' % (token.tok_name[tok_type], repr(string).lstrip('u'))


class Token(collections.namedtuple('Token', 'type string start end line index startpos endpos')):
  """
  TokenInfo is an 8-tuple containing the same 5 fields as the tokens produced by the tokenize
  module, and 3 additional ones useful for this module:

  - [0] .type     Token type (see token.py)
  - [1] .string   Token (a string)
  - [2] .start    Starting (row, column) indices of the token (a 2-tuple of ints)
  - [3] .end      Ending (row, column) indices of the token (a 2-tuple of ints)
  - [4] .line     Original line (string)
  - [5] .index    Index of the token in the list of tokens that it belongs to.
  - [6] .startpos Starting character offset into the input text.
  - [7] .endpos   Ending character offset into the input text.
  """
  def __str__(self):
    # type: () -> str
    return token_repr(self.type, self.string)


def match_token(token, tok_type, tok_str=None):
  # type: (Token, int, Optional[str]) -> bool
  """Returns true if token is of the given type and, if a string is given, has that string."""
  return token.type == tok_type and (tok_str is None or token.string == tok_str)


def expect_token(token, tok_type, tok_str=None):
  # type: (Token, int, Optional[str]) -> None
  """
  Verifies that the given token is of the expected type. If tok_str is given, the token string
  is verified too. If the token doesn't match, raises an informative ValueError.
  """
  if not match_token(token, tok_type, tok_str):
    raise ValueError("Expected token %s, got %s on line %s col %s" % (
      token_repr(tok_type, tok_str), str(token),
      token.start[0], token.start[1] + 1))


def is_non_coding_token(token_type):
  # type: (int) -> bool
  """
  These are considered non-coding tokens, as they don't affect the syntax tree.
  """
  return token_type in (token.NL, token.COMMENT, token.ENCODING)


def generate_tokens(text):
  # type: (str) -> Iterator[TokenInfo]
  """
  Generates standard library tokens for the given code.
  """
  # tokenize.generate_tokens is technically an undocumented API for Python3, but allows us to use the same API as for
  # Python2. See http://stackoverflow.com/a/4952291/328565.
  # FIXME: Remove cast once https://github.com/python/typeshed/issues/7003 gets fixed
  return tokenize.generate_tokens(cast(Callable[[], str], io.StringIO(text).readline))


def iter_children_func(node):
  # type: (AST) -> Callable
  """
  Returns a function which yields all direct children of a AST node,
  skipping children that are singleton nodes.
  The function depends on whether ``node`` is from ``ast`` or from the ``astroid`` module.
  """
  return iter_children_astroid if hasattr(node, 'get_children') else iter_children_ast


def iter_children_astroid(node, include_joined_str=False):
  # type: (NodeNG, bool) -> Union[Iterator, List]
  if not include_joined_str and is_joined_str(node):
    return []

  return node.get_children()


SINGLETONS = {c for n, c in ast.__dict__.items() if isinstance(c, type) and
              issubclass(c, (ast.expr_context, ast.boolop, ast.operator, ast.unaryop, ast.cmpop))}


def iter_children_ast(node, include_joined_str=False):
  # type: (AST, bool) -> Iterator[Union[AST, expr]]
  if not include_joined_str and is_joined_str(node):
    return

  if isinstance(node, ast.Dict):
    # override the iteration order: instead of <all keys>, <all values>,
    # yield keys and values in source order (key1, value1, key2, value2, ...)
    for (key, value) in zip(node.keys, node.values):
      if key is not None:
        yield key
      yield value
    return

  for child in ast.iter_child_nodes(node):
    # Skip singleton children; they don't reflect particular positions in the code and break the
    # assumptions about the tree consisting of distinct nodes. Note that collecting classes
    # beforehand and checking them in a set is faster than using isinstance each time.
    if child.__class__ not in SINGLETONS:
      yield child


stmt_class_names = {n for n, c in ast.__dict__.items()
                    if isinstance(c, type) and issubclass(c, ast.stmt)}
expr_class_names = ({n for n, c in ast.__dict__.items()
                    if isinstance(c, type) and issubclass(c, ast.expr)} |
                    {'AssignName', 'DelName', 'Const', 'AssignAttr', 'DelAttr'})

# These feel hacky compared to isinstance() but allow us to work with both ast and astroid nodes
# in the same way, and without even importing astroid.
def is_expr(node):
  # type: (AstNode) -> bool
  """Returns whether node is an expression node."""
  return node.__class__.__name__ in expr_class_names

def is_stmt(node):
  # type: (AstNode) -> bool
  """Returns whether node is a statement node."""
  return node.__class__.__name__ in stmt_class_names

def is_module(node):
  # type: (AstNode) -> bool
  """Returns whether node is a module node."""
  return node.__class__.__name__ == 'Module'

def is_joined_str(node):
  # type: (AstNode) -> bool
  """Returns whether node is a JoinedStr node, used to represent f-strings."""
  # At the moment, nodes below JoinedStr have wrong line/col info, and trying to process them only
  # leads to errors.
  return node.__class__.__name__ == 'JoinedStr'


def is_expr_stmt(node):
  # type: (AstNode) -> bool
  """Returns whether node is an `Expr` node, which is a statement that is an expression."""
  return node.__class__.__name__ == 'Expr'



CONSTANT_CLASSES: Tuple[Type, ...] = (ast.Constant,)
try:
  from astroid import Const
  CONSTANT_CLASSES += (Const,)
except ImportError:  # pragma: no cover
  # astroid is not available
  pass

def is_constant(node):
  # type: (AstNode) -> bool
  """Returns whether node is a Constant node."""
  return isinstance(node, CONSTANT_CLASSES)


def is_ellipsis(node):
  # type: (AstNode) -> bool
  """Returns whether node is an Ellipsis node."""
  return is_constant(node) and node.value is Ellipsis  # type: ignore


def is_starred(node):
  # type: (AstNode) -> bool
  """Returns whether node is a starred expression node."""
  return node.__class__.__name__ == 'Starred'


def is_slice(node):
  # type: (AstNode) -> bool
  """Returns whether node represents a slice, e.g. `1:2` in `x[1:2]`"""
  # Before 3.9, a tuple containing a slice is an ExtSlice,
  # but this was removed in https://bugs.python.org/issue34822
  return (
      node.__class__.__name__ in ('Slice', 'ExtSlice')
      or (
          node.__class__.__name__ == 'Tuple'
          and any(map(is_slice, cast(ast.Tuple, node).elts))
      )
  )


def is_empty_astroid_slice(node):
  # type: (AstNode) -> bool
  return (
      node.__class__.__name__ == "Slice"
      and not isinstance(node, ast.AST)
      and node.lower is node.upper is node.step is None
  )


# Sentinel value used by visit_tree().
_PREVISIT = object()

def visit_tree(node, previsit, postvisit):
  # type: (Module, Callable[[AstNode, Optional[Token]], Tuple[Optional[Token], Optional[Token]]], Optional[Callable[[AstNode, Optional[Token], Optional[Token]], None]])   -> None
  """
  Scans the tree under the node depth-first using an explicit stack. It avoids implicit recursion
  via the function call stack to avoid hitting 'maximum recursion depth exceeded' error.

  It calls ``previsit()`` and ``postvisit()`` as follows:

  * ``previsit(node, par_value)`` - should return ``(par_value, value)``
        ``par_value`` is as returned from ``previsit()`` of the parent.

  * ``postvisit(node, par_value, value)`` - should return ``value``
        ``par_value`` is as returned from ``previsit()`` of the parent, and ``value`` is as
        returned from ``previsit()`` of this node itself. The return ``value`` is ignored except
        the one for the root node, which is returned from the overall ``visit_tree()`` call.

  For the initial node, ``par_value`` is None. ``postvisit`` may be None.
  """
  if not postvisit:
    postvisit = lambda node, pvalue, value: None

  iter_children = iter_children_func(node)
  done = set()
  ret = None
  stack = [(node, None, _PREVISIT)] # type: List[Tuple[AstNode, Optional[Token], Union[Optional[Token], object]]]
  while stack:
    current, par_value, value = stack.pop()
    if value is _PREVISIT:
      assert current not in done    # protect againt infinite loop in case of a bad tree.
      done.add(current)

      pvalue, post_value = previsit(current, par_value)
      stack.append((current, par_value, post_value))

      # Insert all children in reverse order (so that first child ends up on top of the stack).
      ins = len(stack)
      for n in iter_children(current):
        stack.insert(ins, (n, pvalue, _PREVISIT))
    else:
      ret = postvisit(current, par_value, cast(Optional[Token], value))
  return ret


def walk(node, include_joined_str=False):
  # type: (AST, bool) -> Iterator[Union[Module, AstNode]]
  """
  Recursively yield all descendant nodes in the tree starting at ``node`` (including ``node``
  itself), using depth-first pre-order traversal (yieling parents before their children).

  This is similar to ``ast.walk()``, but with a different order, and it works for both ``ast`` and
  ``astroid`` trees. Also, as ``iter_children()``, it skips singleton nodes generated by ``ast``.

  By default, ``JoinedStr`` (f-string) nodes and their contents are skipped
  because they previously couldn't be handled. Set ``include_joined_str`` to True to include them.
  """
  iter_children = iter_children_func(node)
  done = set()
  stack = [node]
  while stack:
    current = stack.pop()
    assert current not in done    # protect againt infinite loop in case of a bad tree.
    done.add(current)

    yield current

    # Insert all children in reverse order (so that first child ends up on top of the stack).
    # This is faster than building a list and reversing it.
    ins = len(stack)
    for c in iter_children(current, include_joined_str):
      stack.insert(ins, c)


def replace(text, replacements):
  # type: (str, List[Tuple[int, int, str]]) -> str
  """
  Replaces multiple slices of text with new values. This is a convenience method for making code
  modifications of ranges e.g. as identified by ``ASTTokens.get_text_range(node)``. Replacements is
  an iterable of ``(start, end, new_text)`` tuples.

  For example, ``replace("this is a test", [(0, 4, "X"), (8, 9, "THE")])`` produces
  ``"X is THE test"``.
  """
  p = 0
  parts = []
  for (start, end, new_text) in sorted(replacements):
    parts.append(text[p:start])
    parts.append(new_text)
    p = end
  parts.append(text[p:])
  return ''.join(parts)


class NodeMethods:
  """
  Helper to get `visit_{node_type}` methods given a node's class and cache the results.
  """
  def __init__(self):
    # type: () -> None
    self._cache = {} # type: Dict[Union[ABCMeta, type], Callable[[AstNode, Token, Token], Tuple[Token, Token]]]

  def get(self, obj, cls):
    # type: (Any, Union[ABCMeta, type]) -> Callable
    """
    Using the lowercase name of the class as node_type, returns `obj.visit_{node_type}`,
    or `obj.visit_default` if the type-specific method is not found.
    """
    method = self._cache.get(cls)
    if not method:
      name = "visit_" + cls.__name__.lower()
      method = getattr(obj, name, obj.visit_default)
      self._cache[cls] = method
    return method


def patched_generate_tokens(original_tokens):
    # type: (Iterable[TokenInfo]) -> Iterator[TokenInfo]
    """
    Fixes tokens yielded by `tokenize.generate_tokens` to handle more non-ASCII characters in identifiers.
    Workaround for https://github.com/python/cpython/issues/68382.
    Should only be used when tokenizing a string that is known to be valid syntax,
    because it assumes that error tokens are not actually errors.
    Combines groups of consecutive NAME, NUMBER, and/or ERRORTOKEN tokens into a single NAME token.
    """
    group = []  # type: List[tokenize.TokenInfo]
    for tok in original_tokens:
      if (
          tok.type in (tokenize.NAME, tokenize.ERRORTOKEN, tokenize.NUMBER)
          # Only combine tokens if they have no whitespace in between
          and (not group or group[-1].end == tok.start)
      ):
        group.append(tok)
      else:
        for combined_token in combine_tokens(group):
          yield combined_token
        group = []
        yield tok
    for combined_token in combine_tokens(group):
      yield combined_token

def combine_tokens(group):
    # type: (List[tokenize.TokenInfo]) -> List[tokenize.TokenInfo]
    if not any(tok.type == tokenize.ERRORTOKEN for tok in group) or len({tok.line for tok in group}) != 1:
      return group
    return [
      tokenize.TokenInfo(
        type=tokenize.NAME,
        string="".join(t.string for t in group),
        start=group[0].start,
        end=group[-1].end,
        line=group[0].line,
      )
    ]


def last_stmt(node):
  # type: (ast.AST) -> ast.AST
  """
  If the given AST node contains multiple statements, return the last one.
  Otherwise, just return the node.
  """
  child_stmts = [
    child for child in iter_children_func(node)(node)
    if is_stmt(child) or type(child).__name__ in (
      "excepthandler",
      "ExceptHandler",
      "match_case",
      "MatchCase",
      "TryExcept",
      "TryFinally",
    )
  ]
  if child_stmts:
    return last_stmt(child_stmts[-1])
  return node



@lru_cache(maxsize=None)
def fstring_positions_work():
  # type: () -> bool
  """
  The positions attached to nodes inside f-string FormattedValues have some bugs
  that were fixed in Python 3.9.7 in https://github.com/python/cpython/pull/27729.
  This checks for those bugs more concretely without relying on the Python version.
  Specifically this checks:
   - Values with a format spec or conversion
   - Repeated (i.e. identical-looking) expressions
   - f-strings implicitly concatenated over multiple lines.
   - Multiline, triple-quoted f-strings.
  """
  source = """(
    f"a {b}{b} c {d!r} e {f:g} h {i:{j}} k {l:{m:n}}"
    f"a {b}{b} c {d!r} e {f:g} h {i:{j}} k {l:{m:n}}"
    f"{x + y + z} {x} {y} {z} {z} {z!a} {z:z}"
    f'''
    {s} {t}
    {u} {v}
    '''
  )"""
  tree = ast.parse(source)
  name_nodes = [node for node in ast.walk(tree) if isinstance(node, ast.Name)]
  name_positions = [(node.lineno, node.col_offset) for node in name_nodes]
  positions_are_unique = len(set(name_positions)) == len(name_positions)
  correct_source_segments = all(
    ast.get_source_segment(source, node) == node.id
    for node in name_nodes
  )
  return positions_are_unique and correct_source_segments

def annotate_fstring_nodes(tree):
  # type: (ast.AST) -> None
  """
  Add a special attribute `_broken_positions` to nodes inside f-strings
  if the lineno/col_offset cannot be trusted.
  """
  if sys.version_info >= (3, 12):
    # f-strings were weirdly implemented until https://peps.python.org/pep-0701/
    # In Python 3.12, inner nodes have sensible positions.
    return
  for joinedstr in walk(tree, include_joined_str=True):
    if not isinstance(joinedstr, ast.JoinedStr):
      continue
    for part in joinedstr.values:
      # The ast positions of the FormattedValues/Constant nodes span the full f-string, which is weird.
      setattr(part, '_broken_positions', True)  # use setattr for mypy

      if isinstance(part, ast.FormattedValue):
        if not fstring_positions_work():
          for child in walk(part.value):
            setattr(child, '_broken_positions', True)

        if part.format_spec:  # this is another JoinedStr
          # Again, the standard positions span the full f-string.
          setattr(part.format_spec, '_broken_positions', True)