Context extension fix #20
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`opcodes_to_edit_linenums()` now accepts a `context_lines` argument which specifies how many extra lines before and after a non-equal diff chunk should be included in the list of line numbers. This re-introduces the inadvertently broken support for expanding the application of reformatting around edited chunks in case the AST of reformatted code doesn't match the original.
It didn't make sense to try to mark more surrounding lines as edited than there are lines of text in the file. Remove the 1000-line hard cap for the number of extra context lines. Theoretically this could prolong the run time for very long pathological files whose AST partial reformatting fails to maintain unchanged. Good luck trying to come up with such a case, though. If this should happen, it would most probably reveal a bug in Black instead.
This was referenced Jul 8, 2020
Closed
`opcodes_to_edit_linenums()` now limits the last chunk to end at the last line of the file even if the number of context lines is large.
Mystic-Mirage
approved these changes
Jul 9, 2020
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When
git diffwas replaced withdifflib.SequenceMatcherin #11, I failed to also re-implement "context expansion". The equivalent ofgit diff -U<number-of-context-lines>is now properly implemented indiff_and_get_opcodes()again. Additionally, the number of extra context lines can no longer grow beyond the number of lines in the processed file.What context expansion does is:
In case the AST of the original edited file doesn't match with the AST of the partially reformatted one, darker considers one more line before and after every user-edited chunk as part of the chunk. This expansion is repeated one line at a time until the ASTs match.
Context expansion helps is rare cases of two nearby chunks of Black reformatting separated by intact lines. Sometimes applying only one of those nearby chunks causes the AST to change, and context expansion will eventually cause them to be applied together.