Michael Montalbo 7555510bf3 diff: emit -L hunk headers via xdiff's formatter ...

The line-range filter builds its own "@@ -<old> +<new> @@" header for
each range hunk.  For a side with no lines (count 0, such as the old
side of a pure insertion), the begin should be the number of the line
before the change, per the convention git diff and xdl_emit_hunk_hdr()
follow.  The hand-rolled code's begin was one too high; in t4211 this
produced

	@@ -25,0 +18,9 @@

an old begin of 25 in a 24-line file, where git diff would give 24.

Stop hand-rolling the header.  flush_range_hunk() now formats it through
xdiff's own emitter: a new xdiff_emit_hunk_header() helper wraps
xdl_emit_hunk_hdr(), the function that produces every other diff's hunk
headers.  The count-0 begin is then correct by construction, and as a
side effect -L headers match git diff exactly, including its omission of
a count of 1 ("@@ -22 +22 @@" rather than "@@ -22,1 +22,1 @@").

xdiff's hunk callback already hands line_range_hunk_fn() a count-0 begin
decremented, so undo that when seeding the cursors and let the formatter
re-apply the convention once, at emit time.

The off-by-one predates this series, and the two regenerated fixtures
reach it from different origins: no-assertion-error has carried it since
its test was added in ab60c693a2 (line-log: fix assertion error,
2025-08-18), while vanishes-early acquired it when 86e986f166 (line-log:
route -L output through the standard diff pipeline) reshaped its tracked
line into a pure insertion.  vanishes-early also drops its count-1
counts.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2026-06-27 19:52:28 -07:00

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