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AST safety check fails to catch incorrect f-string change
Describe the style change
I wonder if f-strings should be formatted at all.
Examples in the current Black style
print(f"{"|".join(['a','b','c'])}")
Desired style
print(f"{"|".join(['a','b','c'])}")
[!NOTE] There's no change to the input here.
Additional context
Black formats the "|" to become " | " and that affects the output which cannot be desired.
Black formats the snippet like this currently:
print(f"{" | ".join(['a','b','c'])}")
Confirmed this bug:
% python3.12 -m black -c '''print(f"{"|".join(['a','b','c'])}")'''
print(f"{" | ".join([a,b,c])}")
This is related to our lack of nested f-string support (#3746). I suppose our parser misparses this as two strings with an | operator in between, then we reformat it to add spaces around the operator, and the AST safety check doesn't catch it because it ignores leading/trailing whitespace for docstring reasons.
Other than adding actual support for this syntax, which is tracked in #3746, we should catch this in the AST safety check by being less lenient about the whitespace changes we allow in strings.
Thank you for confirming this issue. I work around it like so:
# fmt: off
print(f"{"|".join(['a','b','c'])}")
# fmt: on
Thank you for addressing this. Can the fix be expected in 24.2.1 or what's the next version that will include the fix?
I just released 24.3.0 which includes this fix.
I still have to wrap the code to not be formatted like this:
# fmt: off
table += f"|{c}|{" | ".join(cols)}|\n"
# fmt: on
[!WARNING] error: cannot format snapshot_manager/snapshot_manager/build_status.py: INTERNAL ERROR: Black produced code that is not equivalent to the source. Please report a bug on https://github.com/psf/black/issues. This diff might be helpful: /tmp/blk_aym4688c.log
$ cat /tmp/blk_aym4688c.log
--- src
+++ dst
@@ -6797,11 +6797,11 @@
value=
Constant(
kind=
None, # NoneType
value=
- '|', # str
+ ' | ', # str
) # /Constant
) # /Attribute
keywords=
) # /Call
) # /FormattedValue