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Fix incorrect f-string tokenization (#4332)
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@JelleZijlstra
JelleZijlstra authored Apr 25, 2024
1 parent ba88fc3 commit e4aaa8a
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2 changes: 2 additions & 0 deletions CHANGES.md
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,8 @@

<!-- Changes to the parser or to version autodetection -->

- Fix regression where certain complex f-strings failed to parse (#4332)

### Performance

<!-- Changes that improve Black's performance. -->
Expand Down
163 changes: 120 additions & 43 deletions src/blib2to3/pgen2/tokenize.py
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Original file line number Diff line number Diff line change
Expand Up @@ -480,6 +480,88 @@ def _split_fstring_start_and_middle(token: str) -> Tuple[str, str]:
raise ValueError(f"Token {token!r} is not a valid f-string start")


STATE_NOT_FSTRING: Final = 0 # not in an f-string
STATE_MIDDLE: Final = 1 # in the string portion of an f-string (outside braces)
STATE_IN_BRACES: Final = 2 # between braces in an f-string
# in the format specifier (between the colon and the closing brace)
STATE_IN_COLON: Final = 3


class FStringState:
"""Keeps track of state around f-strings.
The tokenizer should call the appropriate method on this class when
it transitions to a different part of an f-string. This is needed
because the tokenization depends on knowing where exactly we are in
the f-string.
For example, consider the following f-string:
f"a{1:b{2}c}d"
The following is the tokenization of this string and the states
tracked by this class:
1,0-1,2: FSTRING_START 'f"' # [STATE_NOT_FSTRING, STATE_MIDDLE]
1,2-1,3: FSTRING_MIDDLE 'a'
1,3-1,4: LBRACE '{' # [STATE_NOT_FSTRING, STATE_IN_BRACES]
1,4-1,5: NUMBER '1'
1,5-1,6: OP ':' # [STATE_NOT_FSTRING, STATE_IN_COLON]
1,6-1,7: FSTRING_MIDDLE 'b'
1,7-1,8: LBRACE '{' # [STATE_NOT_FSTRING, STATE_IN_COLON, STATE_IN_BRACES]
1,8-1,9: NUMBER '2'
1,9-1,10: RBRACE '}' # [STATE_NOT_FSTRING, STATE_IN_COLON]
1,10-1,11: FSTRING_MIDDLE 'c'
1,11-1,12: RBRACE '}' # [STATE_NOT_FSTRING, STATE_MIDDLE]
1,12-1,13: FSTRING_MIDDLE 'd'
1,13-1,14: FSTRING_END '"' # [STATE_NOT_FSTRING]
1,14-1,15: NEWLINE '\n'
2,0-2,0: ENDMARKER ''
Notice that the nested braces in the format specifier are represented
by adding a STATE_IN_BRACES entry to the state stack. The stack is
also used if there are nested f-strings.
"""

def __init__(self) -> None:
self.stack: List[int] = [STATE_NOT_FSTRING]

def is_in_fstring_expression(self) -> bool:
return self.stack[-1] not in (STATE_MIDDLE, STATE_NOT_FSTRING)

def current(self) -> int:
return self.stack[-1]

def enter_fstring(self) -> None:
self.stack.append(STATE_MIDDLE)

def leave_fstring(self) -> None:
state = self.stack.pop()
assert state == STATE_MIDDLE

def consume_lbrace(self) -> None:
current_state = self.stack[-1]
if current_state == STATE_MIDDLE:
self.stack[-1] = STATE_IN_BRACES
elif current_state == STATE_IN_COLON:
self.stack.append(STATE_IN_BRACES)
else:
assert False, current_state

def consume_rbrace(self) -> None:
current_state = self.stack[-1]
assert current_state in (STATE_IN_BRACES, STATE_IN_COLON)
if len(self.stack) > 1 and self.stack[-2] == STATE_IN_COLON:
self.stack.pop()
else:
self.stack[-1] = STATE_MIDDLE

def consume_colon(self) -> None:
assert self.stack[-1] == STATE_IN_BRACES, self.stack
self.stack[-1] = STATE_IN_COLON


def generate_tokens(
readline: Callable[[], str], grammar: Optional[Grammar] = None
) -> Iterator[GoodTokenInfo]:
Expand All @@ -498,12 +580,10 @@ def generate_tokens(
and the line on which the token was found. The line passed is the
logical line; continuation lines are included.
"""
lnum = parenlev = fstring_level = continued = 0
lnum = parenlev = continued = 0
parenlev_stack: List[int] = []
inside_fstring_braces = False
inside_fstring_colon = False
fstring_state = FStringState()
formatspec = ""
bracelev = 0
numchars: Final[str] = "0123456789"
contstr, needcont = "", 0
contline: Optional[str] = None
Expand Down Expand Up @@ -542,13 +622,15 @@ def generate_tokens(
spos = strstart
epos = (lnum, end)
tokenline = contline + line
if fstring_level == 0 and not is_fstring_start(token):
if (
fstring_state.current() == STATE_NOT_FSTRING
and not is_fstring_start(token)
):
yield (STRING, token, spos, epos, tokenline)
endprog_stack.pop()
parenlev = parenlev_stack.pop()
else:
if is_fstring_start(token):
fstring_level += 1
fstring_start, token = _split_fstring_start_and_middle(token)
fstring_start_epos = (lnum, spos[1] + len(fstring_start))
yield (
Expand All @@ -558,6 +640,7 @@ def generate_tokens(
fstring_start_epos,
tokenline,
)
fstring_state.enter_fstring()
# increase spos to the end of the fstring start
spos = fstring_start_epos

Expand All @@ -572,7 +655,7 @@ def generate_tokens(
line,
)
yield (LBRACE, lbrace, lbrace_spos, epos, line)
inside_fstring_braces = True
fstring_state.consume_lbrace()
else:
if token.endswith(('"""', "'''")):
fstring_middle, fstring_end = token[:-3], token[-3:]
Expand All @@ -594,11 +677,9 @@ def generate_tokens(
epos,
line,
)
fstring_level -= 1
fstring_state.leave_fstring()
endprog_stack.pop()
parenlev = parenlev_stack.pop()
if fstring_level > 0:
inside_fstring_braces = True
pos = end
contstr, needcont = "", 0
contline = None
Expand All @@ -619,7 +700,11 @@ def generate_tokens(
continue

# new statement
elif parenlev == 0 and not continued and not inside_fstring_braces:
elif (
parenlev == 0
and not continued
and not fstring_state.is_in_fstring_expression()
):
if not line:
break
column = 0
Expand Down Expand Up @@ -687,7 +772,7 @@ def generate_tokens(
continued = 0

while pos < max:
if fstring_level > 0 and not inside_fstring_braces:
if fstring_state.current() == STATE_MIDDLE:
endprog = endprog_stack[-1]
endmatch = endprog.match(line, pos)
if endmatch: # all on one line
Expand Down Expand Up @@ -718,14 +803,12 @@ def generate_tokens(
(lnum, end),
line,
)
fstring_level -= 1
fstring_state.leave_fstring()
endprog_stack.pop()
parenlev = parenlev_stack.pop()
if fstring_level > 0:
inside_fstring_braces = True
else:
yield (LBRACE, "{", (lnum, end - 1), (lnum, end), line)
inside_fstring_braces = True
fstring_state.consume_lbrace()
pos = end
continue
else: # multiple lines
Expand All @@ -734,7 +817,7 @@ def generate_tokens(
contline = line
break

if inside_fstring_colon:
if fstring_state.current() == STATE_IN_COLON:
match = fstring_middle_after_colon.match(line, pos)
if match is None:
formatspec += line[pos:]
Expand All @@ -754,15 +837,19 @@ def generate_tokens(
formatspec = ""

if brace_or_nl == "{":
yield (OP, "{", (lnum, brace_start), (lnum, brace_end), line)
bracelev += 1
yield (LBRACE, "{", (lnum, brace_start), (lnum, brace_end), line)
fstring_state.consume_lbrace()
end = brace_end
elif brace_or_nl == "}":
yield (RBRACE, "}", (lnum, brace_start), (lnum, brace_end), line)
fstring_state.consume_rbrace()
end = brace_end
formatspec_start = (lnum, brace_end)

inside_fstring_colon = False
pos = end
continue

if inside_fstring_braces and parenlev == 0:
if fstring_state.current() == STATE_IN_BRACES and parenlev == 0:
match = bang.match(line, pos)
if match:
start, end = match.span(1)
Expand All @@ -774,7 +861,7 @@ def generate_tokens(
if match:
start, end = match.span(1)
yield (OP, ":", (lnum, start), (lnum, end), line)
inside_fstring_colon = True
fstring_state.consume_colon()
formatspec_start = (lnum, end)
pos = end
continue
Expand All @@ -791,7 +878,7 @@ def generate_tokens(
yield (NUMBER, token, spos, epos, line)
elif initial in "\r\n":
newline = NEWLINE
if parenlev > 0 or inside_fstring_braces:
if parenlev > 0 or fstring_state.is_in_fstring_expression():
newline = NL
elif async_def:
async_def_nl = True
Expand All @@ -813,7 +900,7 @@ def generate_tokens(
parenlev = 0
if is_fstring_start(token):
yield (FSTRING_START, token, spos, epos, line)
fstring_level += 1
fstring_state.enter_fstring()

endmatch = endprog.match(line, pos)
if endmatch: # all on one line
Expand Down Expand Up @@ -848,11 +935,9 @@ def generate_tokens(
epos,
line,
)
fstring_level -= 1
fstring_state.leave_fstring()
endprog_stack.pop()
parenlev = parenlev_stack.pop()
if fstring_level > 0:
inside_fstring_braces = True
else:
fstring_middle, lbrace = token[:-1], token[-1]
fstring_middle_epos = lbrace_spos = (lnum, end - 1)
Expand All @@ -864,7 +949,7 @@ def generate_tokens(
line,
)
yield (LBRACE, lbrace, lbrace_spos, epos, line)
inside_fstring_braces = True
fstring_state.consume_lbrace()
pos = end
else:
# multiple lines
Expand Down Expand Up @@ -919,7 +1004,7 @@ def generate_tokens(

start_epos = (lnum, start + offset)
yield (FSTRING_START, fstring_start, spos, start_epos, line)
fstring_level += 1
fstring_state.enter_fstring()
endprog = endprogs[fstring_start]
endprog_stack.append(endprog)
parenlev_stack.append(parenlev)
Expand All @@ -940,16 +1025,14 @@ def generate_tokens(
end_spos = (lnum, end_offset)
end_epos = (lnum, end_offset + 1)
yield (FSTRING_END, token[-1], end_spos, end_epos, line)
fstring_level -= 1
fstring_state.leave_fstring()
endprog_stack.pop()
parenlev = parenlev_stack.pop()
if fstring_level > 0:
inside_fstring_braces = True
else:
end_spos = (lnum, end_offset)
end_epos = (lnum, end_offset + 1)
yield (LBRACE, "{", end_spos, end_epos, line)
inside_fstring_braces = True
fstring_state.consume_lbrace()

elif initial.isidentifier(): # ordinary name
if token in ("async", "await"):
Expand Down Expand Up @@ -998,19 +1081,13 @@ def generate_tokens(
elif (
initial == "}"
and parenlev == 0
and bracelev == 0
and fstring_level > 0
and fstring_state.is_in_fstring_expression()
):
yield (RBRACE, token, spos, epos, line)
inside_fstring_braces = False
fstring_state.consume_rbrace()
formatspec_start = epos
else:
if parenlev == 0 and bracelev > 0 and initial == "}":
bracelev -= 1
# if we're still inside fstrings, we're still part of the format spec
if inside_fstring_braces:
inside_fstring_colon = True
formatspec_start = (lnum, pos)
elif initial in "([{":
if initial in "([{":
parenlev += 1
elif initial in ")]}":
parenlev -= 1
Expand Down
8 changes: 8 additions & 0 deletions tests/data/cases/pep_701.py
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Original file line number Diff line number Diff line change
Expand Up @@ -119,6 +119,10 @@
level=0,
)

f"{1:{f'{2}'}}"
f'{1:{f'{2}'}}'
f'{1:{2}d}'

f'{{\\"kind\\":\\"ConfigMap\\",\\"metadata\\":{{\\"annotations\\":{{}},\\"name\\":\\"cluster-info\\",\\"namespace\\":\\"amazon-cloudwatch\\"}}}}'

# output
Expand Down Expand Up @@ -243,4 +247,8 @@
level=0,
)

f"{1:{f'{2}'}}"
f"{1:{f'{2}'}}"
f"{1:{2}d}"

f'{{\\"kind\\":\\"ConfigMap\\",\\"metadata\\":{{\\"annotations\\":{{}},\\"name\\":\\"cluster-info\\",\\"namespace\\":\\"amazon-cloudwatch\\"}}}}'

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