def _patch_special_syntax(self):
"""Takes an fstring (and its prefix, ie "f") that may contain
xonsh expressions as its field values and substitues them for
a call to __xonsh__.eval_fstring_field as needed.
"""
prelen = len(self.prefix)
quote = self.fstring[prelen]
if self.fstring[prelen + 1] == quote:
quote *= 3
template = self.fstring[prelen + len(quote) : -len(quote)]
while True:
repl = self.prefix + quote + template + quote
try:
res = pyparse(repl)
break
except SyntaxError as e:
# The e.text attribute is expected to contain the failing
# expression, e.g. "($HOME)" for f"{$HOME}" string.
if e.text is None or e.text[0] != "(":
raise
error_expr = e.text[1:-1]
epos = template.find(error_expr)
if epos < 0:
raise
# We can olny get here in the case of handled SyntaxError.
# Patch the last error and start over.
xonsh_field = (error_expr, self.filename if self.filename else None)
field_id = id(xonsh_field)
self.fields[field_id] = xonsh_field
eval_field = f"__xonsh__.eval_fstring_field({field_id})"
template = template[:epos] + eval_field + template[epos + len(error_expr) :]
self.repl = repl
self.res = res.body[0].value
def _unpatch_strings(self):
"""Reverts false-positive field matches within strings."""
reparse = False
for node in ast.walk(self.res):
if isinstance(node, ast.Constant) and isinstance(node.value, str):
value = node.value
elif isinstance(node, ast.Str):
value = node.s
else:
continue
match = RE_FSTR_FIELD_WRAPPER.search(value)
if match is None:
continue
field = self.fields.pop(int(match.group(2)), None)
if field is None:
continue
self.repl = self.repl.replace(match.group(1), field[0], 1)
reparse = True
if reparse:
self.res = pyparse(self.repl).body[0].value