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parsing.py
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parsing.py
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"""
Parse Python code and perform AST validation.
"""
import ast
import platform
import sys
from typing import Iterable, Iterator, List, Set, Union, Tuple
# lib2to3 fork
from blib2to3.pytree import Node, Leaf
from blib2to3 import pygram, pytree
from blib2to3.pgen2 import driver
from blib2to3.pgen2.grammar import Grammar
from blib2to3.pgen2.parse import ParseError
from black.mode import TargetVersion, Feature, supports_feature
from black.nodes import syms
_IS_PYPY = platform.python_implementation() == "PyPy"
try:
from typed_ast import ast3, ast27
except ImportError:
# Either our python version is too low, or we're on pypy
if sys.version_info < (3, 7) or (sys.version_info < (3, 8) and not _IS_PYPY):
print(
"The typed_ast package is required but not installed.\n"
"You can upgrade to Python 3.8+ or install typed_ast with\n"
"`python3 -m pip install typed-ast`.",
file=sys.stderr,
)
sys.exit(1)
else:
ast3 = ast27 = ast
class InvalidInput(ValueError):
"""Raised when input source code fails all parse attempts."""
def get_grammars(target_versions: Set[TargetVersion]) -> List[Grammar]:
if not target_versions:
# No target_version specified, so try all grammars.
return [
# Python 3.7+
pygram.python_grammar_no_print_statement_no_exec_statement_async_keywords,
# Python 3.0-3.6
pygram.python_grammar_no_print_statement_no_exec_statement,
# Python 2.7 with future print_function import
pygram.python_grammar_no_print_statement,
# Python 2.7
pygram.python_grammar,
]
if all(version.is_python2() for version in target_versions):
# Python 2-only code, so try Python 2 grammars.
return [
# Python 2.7 with future print_function import
pygram.python_grammar_no_print_statement,
# Python 2.7
pygram.python_grammar,
]
# Python 3-compatible code, so only try Python 3 grammar.
grammars = []
# If we have to parse both, try to parse async as a keyword first
if not supports_feature(target_versions, Feature.ASYNC_IDENTIFIERS):
# Python 3.7+
grammars.append(
pygram.python_grammar_no_print_statement_no_exec_statement_async_keywords
)
if not supports_feature(target_versions, Feature.ASYNC_KEYWORDS):
# Python 3.0-3.6
grammars.append(pygram.python_grammar_no_print_statement_no_exec_statement)
# At least one of the above branches must have been taken, because every Python
# version has exactly one of the two 'ASYNC_*' flags
return grammars
def lib2to3_parse(src_txt: str, target_versions: Iterable[TargetVersion] = ()) -> Node:
"""Given a string with source, return the lib2to3 Node."""
if not src_txt.endswith("\n"):
src_txt += "\n"
for grammar in get_grammars(set(target_versions)):
drv = driver.Driver(grammar, pytree.convert)
try:
result = drv.parse_string(src_txt, True)
break
except ParseError as pe:
lineno, column = pe.context[1]
lines = src_txt.splitlines()
try:
faulty_line = lines[lineno - 1]
except IndexError:
faulty_line = "<line number missing in source>"
exc = InvalidInput(f"Cannot parse: {lineno}:{column}: {faulty_line}")
else:
raise exc from None
if isinstance(result, Leaf):
result = Node(syms.file_input, [result])
return result
def lib2to3_unparse(node: Node) -> str:
"""Given a lib2to3 node, return its string representation."""
code = str(node)
return code
def parse_single_version(
src: str, version: Tuple[int, int]
) -> Union[ast.AST, ast3.AST, ast27.AST]:
filename = "<unknown>"
# typed_ast is needed because of feature version limitations in the builtin ast
if sys.version_info >= (3, 8) and version >= (3,):
return ast.parse(src, filename, feature_version=version)
elif version >= (3,):
if _IS_PYPY:
return ast3.parse(src, filename)
else:
return ast3.parse(src, filename, feature_version=version[1])
elif version == (2, 7):
return ast27.parse(src)
raise AssertionError("INTERNAL ERROR: Tried parsing unsupported Python version!")
def parse_ast(src: str) -> Union[ast.AST, ast3.AST, ast27.AST]:
# TODO: support Python 4+ ;)
versions = [(3, minor) for minor in range(3, sys.version_info[1] + 1)]
if ast27.__name__ != "ast":
versions.append((2, 7))
first_error = ""
for version in sorted(versions, reverse=True):
try:
return parse_single_version(src, version)
except SyntaxError as e:
if not first_error:
first_error = str(e)
raise SyntaxError(first_error)
def stringify_ast(
node: Union[ast.AST, ast3.AST, ast27.AST], depth: int = 0
) -> Iterator[str]:
"""Simple visitor generating strings to compare ASTs by content."""
node = fixup_ast_constants(node)
yield f"{' ' * depth}{node.__class__.__name__}("
for field in sorted(node._fields): # noqa: F402
# TypeIgnore will not be present using pypy < 3.8, so need for this
if not (_IS_PYPY and sys.version_info < (3, 8)):
# TypeIgnore has only one field 'lineno' which breaks this comparison
type_ignore_classes = (ast3.TypeIgnore, ast27.TypeIgnore)
if sys.version_info >= (3, 8):
type_ignore_classes += (ast.TypeIgnore,)
if isinstance(node, type_ignore_classes):
break
try:
value = getattr(node, field)
except AttributeError:
continue
yield f"{' ' * (depth+1)}{field}="
if isinstance(value, list):
for item in value:
# Ignore nested tuples within del statements, because we may insert
# parentheses and they change the AST.
if (
field == "targets"
and isinstance(node, (ast.Delete, ast3.Delete, ast27.Delete))
and isinstance(item, (ast.Tuple, ast3.Tuple, ast27.Tuple))
):
for item in item.elts:
yield from stringify_ast(item, depth + 2)
elif isinstance(item, (ast.AST, ast3.AST, ast27.AST)):
yield from stringify_ast(item, depth + 2)
elif isinstance(value, (ast.AST, ast3.AST, ast27.AST)):
yield from stringify_ast(value, depth + 2)
else:
# Constant strings may be indented across newlines, if they are
# docstrings; fold spaces after newlines when comparing. Similarly,
# trailing and leading space may be removed.
# Note that when formatting Python 2 code, at least with Windows
# line-endings, docstrings can end up here as bytes instead of
# str so make sure that we handle both cases.
if (
isinstance(node, ast.Constant)
and field == "value"
and isinstance(value, (str, bytes))
):
lineend = "\n" if isinstance(value, str) else b"\n"
# To normalize, we strip any leading and trailing space from
# each line...
stripped = [line.strip() for line in value.splitlines()]
normalized = lineend.join(stripped) # type: ignore[attr-defined]
# ...and remove any blank lines at the beginning and end of
# the whole string
normalized = normalized.strip()
else:
normalized = value
yield f"{' ' * (depth+2)}{normalized!r}, # {value.__class__.__name__}"
yield f"{' ' * depth}) # /{node.__class__.__name__}"
def fixup_ast_constants(
node: Union[ast.AST, ast3.AST, ast27.AST]
) -> Union[ast.AST, ast3.AST, ast27.AST]:
"""Map ast nodes deprecated in 3.8 to Constant."""
if isinstance(node, (ast.Str, ast3.Str, ast27.Str, ast.Bytes, ast3.Bytes)):
return ast.Constant(value=node.s)
if isinstance(node, (ast.Num, ast3.Num, ast27.Num)):
return ast.Constant(value=node.n)
if isinstance(node, (ast.NameConstant, ast3.NameConstant)):
return ast.Constant(value=node.value)
return node