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Finish the change started in the preceding commit and allow an early return from "xdiff_emit_line_fn" callbacks, this will allows diffcore-pickaxe.c to save itself redundant work. Our xdiff interface also had the limitation of not being able to abort early since the beginning, seemaintd9ea73e056
(combine-diff: refactor built-in xdiff interface., 2006-04-05). Although at that time "xdiff_emit_line_fn" was called "xdiff_emit_consume_fn", and "xdiff_emit_hunk_fn" didn't exist yet. There was some work in this area of xdiff-interface.[ch] recently with3b40a090fd
(diff: avoid generating unused hunk header lines, 2018-11-02) and7c61e25fbf
(diff: use hunk callback for word-diff, 2018-11-02). In combination those two changes allow us to not do any work on the hunks and diff at all, but didn't change the status quo with regards to consumers that e.g. want the diff lines, but might want to abort early. Whereas now we can abort e.g. on the first "-line" of a 1000 line diff if that's all we needed. This interface is rather scary as noted in the comment to xdiff-interface.h being added here, as noted there a future change could add more exit codes, and hack xdl_emit_diff() and friends to ignore or skip things more selectively as a result. I did not see an inherent reason for why xdl_emit_{diffrec,record}() could not be changed to ferry the "xdiff_emit_line_fn" error code upwards instead of returning -1 on all "ret < 0". But doing so would require corresponding changes in xdl_emit_diff(), xdl_diff(). I didn't see any issue with narrowly doing that to accomplish what I needed here, but it would leave xdiff's own return values in an inconsistent state. Instead I've left it at returning a more conventional (for git's own codebase) 1 for an early return, and translating it (or rather, all non-zero) to -1 for xdiff's consumption. The reason for most of the "stop" complexity in xdiff_outf() is because we want to be able to abort early, but do so in a way that doesn't skip the appropriate strbuf_reset() invocations. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>


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