Fix fmt: skip failing to parse multiline case statements with backslash continuation#5123
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ParamChordiya wants to merge 5 commits intopsf:mainfrom
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Fix fmt: skip failing to parse multiline case statements with backslash continuation#5123ParamChordiya wants to merge 5 commits intopsf:mainfrom
ParamChordiya wants to merge 5 commits intopsf:mainfrom
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…sh continuation When # fmt: skip appears on a multiline case pattern using backslash line continuation (e.g. case A \ | B: # fmt: skip), the node traversal in _generate_ignored_nodes_from_fmt_skip stopped prematurely. The while loop used "\n" not in prefix to detect line boundaries, but the | token's prefix contains \<newline> (a line continuation), which was misread as a real line break. Only the second half of the or-pattern was collected, producing garbled output that failed to re-parse on the second formatting pass. Fix by adding _prefix_has_real_newline() which treats a newline preceded by a backslash as a continuation rather than a boundary. The traversal now walks back through the entire or-pattern and collects all nodes correctly. Fixes psf#5122
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Summary
casestatement with# fmt: skip#5122:black >= 26crashes withCannot parsewhen# fmt: skipis applied to a multilinecasepattern using backslash line continuation (\)_prefix_has_real_newline()helper to distinguish real newlines from backslash-continued ones_generate_ignored_nodes_from_fmt_skipto use the new helperfmtskip14.pycovering the reported scenario and multiple backslash continuationsRoot cause
_generate_ignored_nodes_from_fmt_skipwalks backward through the CST to collect all nodes on the same logical line as# fmt: skip. The while condition used"\n" not in current_node.prefixto detect a line boundary and stop.For a multiline
casepattern like:the
|token has prefix' \\\n '(backslash + newline). The old check treated this as a line boundary, so traversal stopped after collecting only the second group and the colon — missing the first group entirely. The resultingSTANDALONE_COMMENTwas malformed, and the second formatting pass crashed with a parse error.Fix
_prefix_has_real_newline(prefix)returnsTrueonly for bare newlines (not preceded by\). The while loop now continues through backslash continuations and collects the entire or-pattern correctly.Test plan
python -m pytest tests/test_format.py -q— 212 passed (includes newfmtskip14)python -m pytest tests/test_black.py -q --deselect tests/test_black.py::BlackTestCase::test_code_option_safe— 158 passed (pre-existing failure excluded)casestatement with# fmt: skip#5122 is left unchanged byblack