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# Copyright (c) Meta Platforms, Inc. and affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
#
import itertools
import re
from typing import Callable, cast, List, Sequence
import libcst as cst
import libcst.matchers as m
from libcst.codemod import VisitorBasedCodemodCommand
USE_FSTRING_SIMPLE_EXPRESSION_MAX_LENGTH = 30
def _match_simple_string(node: cst.CSTNode) -> bool:
if isinstance(node, cst.SimpleString) and not node.prefix.lower().startswith("b"):
# SimpleString can be a bytes and fstring don't support bytes
return re.fullmatch("[^%]*(%s[^%]*)+", node.raw_value) is not None
return False
def _gen_match_simple_expression(module: cst.Module) -> Callable[[cst.CSTNode], bool]:
def _match_simple_expression(node: cst.CSTNode) -> bool:
# either each element in Tuple is simple expression or the entire expression is simple.
if (
isinstance(node, cst.Tuple)
and all(
len(module.code_for_node(elm.value))
< USE_FSTRING_SIMPLE_EXPRESSION_MAX_LENGTH
for elm in node.elements
)
) or len(module.code_for_node(node)) < USE_FSTRING_SIMPLE_EXPRESSION_MAX_LENGTH:
return True
return False
return _match_simple_expression
class EscapeStringQuote(cst.CSTTransformer):
def __init__(self, quote: str) -> None:
self.quote = quote
super().__init__()
def leave_SimpleString(
self, original_node: cst.SimpleString, updated_node: cst.SimpleString
) -> cst.SimpleString:
if self.quote == original_node.quote:
for quo in ["'", '"', "'''", '"""']:
if quo != original_node.quote and quo not in original_node.raw_value:
escaped_string = cst.SimpleString(
original_node.prefix + quo + original_node.raw_value + quo
)
if escaped_string.evaluated_value != original_node.evaluated_value:
raise ValueError(
f"Failed to escape string:\n original:{original_node.value}\n escaped:{escaped_string.value}"
)
else:
return escaped_string
raise ValueError(
f"Cannot find a good quote for escaping the SimpleString: {original_node.value}"
)
return original_node
class ConvertPercentFormatStringCommand(VisitorBasedCodemodCommand):
DESCRIPTION: str = "Converts simple % style string format to f-string."
def leave_BinaryOperation(
self, original_node: cst.BinaryOperation, updated_node: cst.BinaryOperation
) -> cst.BaseExpression:
expr_key = "expr"
extracts = m.extract(
original_node,
m.BinaryOperation(
# pyre-fixme[6]: Expected `Union[m._matcher_base.AllOf[typing.Union[m...
left=m.MatchIfTrue(_match_simple_string),
operator=m.Modulo(),
# pyre-fixme[6]: Expected `Union[m._matcher_base.AllOf[typing.Union[m...
right=m.SaveMatchedNode(
m.MatchIfTrue(_gen_match_simple_expression(self.module)),
expr_key,
),
),
)
if extracts:
exprs = extracts[expr_key]
exprs = (exprs,) if not isinstance(exprs, Sequence) else exprs
parts = []
simple_string = cst.ensure_type(original_node.left, cst.SimpleString)
innards = simple_string.raw_value.replace("{", "{{").replace("}", "}}")
tokens = innards.split("%s")
token = tokens[0]
if len(token) > 0:
parts.append(cst.FormattedStringText(value=token))
expressions: List[cst.CSTNode] = list(
*itertools.chain(
(
[elm.value for elm in expr.elements]
if isinstance(expr, cst.Tuple)
else [expr]
)
for expr in exprs
)
)
escape_transformer = EscapeStringQuote(simple_string.quote)
i = 1
while i < len(tokens):
if i - 1 >= len(expressions):
# the %-string doesn't come with same number of elements in tuple
return original_node
try:
parts.append(
cst.FormattedStringExpression(
expression=cast(
cst.BaseExpression,
expressions[i - 1].visit(escape_transformer),
)
)
)
except Exception:
return original_node
token = tokens[i]
if len(token) > 0:
parts.append(cst.FormattedStringText(value=token))
i += 1
start = f"f{simple_string.prefix}{simple_string.quote}"
return cst.FormattedString(
parts=parts, start=start, end=simple_string.quote
)
return original_node
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