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@snowsignal snowsignal commented Feb 14, 2024

Summary

Fixes #9895

The cause for this panic came from an offset error in the code. When analyzing a hypothetical f-string, we attempt to re-parse it as an f-string, and use the AST data to determine, among other things, whether the format specifiers are correct. To determine the 'correctness' of a format specifier, we actually have to re-parse the format specifier, and this is where the issue lies. To get the source text for the specifier, we were taking a slice from the original file source text... even though the AST data for the specifier belongs to the standalone parsed f-string expression, meaning that the ranges are going to be way off. In a file with Unicode, this can cause panics if the slice is inside a char boundary.

To fix this, we now slice from the temporary source we created earlier to parse the literal as an f-string.

Test Plan

The RUF027 snapshot test was amended to include a string with format specifiers which we should be calling out. This is to ensure we do slice format specifiers from the source text correctly.

@snowsignal snowsignal added the bug Something isn't working label Feb 14, 2024
@snowsignal snowsignal force-pushed the jane/ruf027/slice-panic-fix branch from bd7edd0 to dee73f6 Compare February 14, 2024 20:13
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github-actions bot commented Feb 14, 2024

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

ℹ️ ecosystem check detected linter changes. (+1 -0 violations, +0 -0 fixes in 1 projects; 42 projects unchanged)

pandas-dev/pandas (+1 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview

+ pandas/io/formats/format.py:1919:26: RUF027 Possible f-string without an `f` prefix

Changes by rule (1 rules affected)

code total + violation - violation + fix - fix
RUF027 1 1 0 0 0

@snowsignal snowsignal enabled auto-merge (squash) February 16, 2024 19:57
@snowsignal snowsignal merged commit 20217e9 into main Feb 16, 2024
@snowsignal snowsignal deleted the jane/ruf027/slice-panic-fix branch February 16, 2024 20:04
nkxxll pushed a commit to nkxxll/ruff that referenced this pull request Mar 10, 2024
## Summary

Fixes astral-sh#9895 

The cause for this panic came from an offset error in the code. When
analyzing a hypothetical f-string, we attempt to re-parse it as an
f-string, and use the AST data to determine, among other things, whether
the format specifiers are correct. To determine the 'correctness' of a
format specifier, we actually have to re-parse the format specifier, and
this is where the issue lies. To get the source text for the specifier,
we were taking a slice from the original file source text... even though
the AST data for the specifier belongs to the standalone parsed f-string
expression, meaning that the ranges are going to be way off. In a file
with Unicode, this can cause panics if the slice is inside a char
boundary.

To fix this, we now slice from the temporary source we created earlier
to parse the literal as an f-string.

## Test Plan

The RUF027 snapshot test was amended to include a string with format
specifiers which we _should_ be calling out. This is to ensure we do
slice format specifiers from the source text correctly.
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Rule RUF027 cause panic

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