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Michael Montalbo
f5488427a3
The diff-hunks store has a writer, but nothing fills it. Teach
builtin_diffstat() to do so: on a warming run (a writer is attached), a
modified pair's stat is produced by collecting the pair's hunk
coordinates instead of emitting text, the counts are summed from those
hunks, and the pair is recorded. A run without a writer is unchanged,
and nothing reads the store yet; the read side arrives next.
The store records one context-free entry per pair, and only for a
trim-stable pair: one whose zero-context trimmed diff (what blame will
read) and untrimmed diff (whose counts a nonzero-context stat matches)
are identical. The warming path computes both and hands them to
diff_hunks_writer_record_stable(), new here, which records only when
they agree; a divergent pair is never recorded and every consumer
computes it. The warming run displays the counts it shows a store-less
run: the trimmed ones, since xdi_diff trims at zero context, while the
untrimmed counts serve only the stability comparison.
Not everything the stat path computes may be recorded.
--ignore-blank-lines is part of the key, but it coalesces hunks
differently between the text-emitting and coordinate-callback paths, so
a recorded entry would not match a store-less run's --stat. -I
patterns, --anchored, and break detection (-B) shape the diff outside
the key entirely; the guard for those three sits in this consumer for
now and moves into the store's own provider when it registers, next. A
"log -L" range-scoped stat is not the whole-pair diff the key describes,
so it does not record. Recording also requires both sides to be valid
regular files whose blobs the key can name: a working-tree side,
textconv output, or a gitlink has no usable id.
"git diff", "git log", "git show", and "git diff-tree" with the --stat,
--numstat, and --shortstat formats attach a writer when writing is
enabled and flush it when the traversal finishes, so a warming run such
as
GIT_DIFF_HUNKS_WRITE=1 git log --all --stat >/dev/null
fills the cache as a side effect of the diff work the command already
does. Writing is controlled by diffHunks.write and GIT_DIFF_HUNKS_WRITE.
Add the write half of t4220:
- ordinary commands never create the store, and creation is gated off
by default, the environment overriding the config;
- a warming run builds a store that verifies, and a second refreshes it
in place;
- a warming run displays parity at zero context on a trim-divergent
pair, committed as a fixture (small synthetic pairs cannot diverge:
minimal diffs add and delete equal counts, and trimming preserves
that);
- binary and mode-only pairs do not break the writer;
- a corrupt store is discarded at seed;
- verify and clear run against the files a warming run builds.
Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
56 lines
2.1 KiB
Plaintext
56 lines
2.1 KiB
Plaintext
t4220 diff-hunks test fixtures
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==============================
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trim-divergent-old, trim-divergent-new
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--------------------------------------
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Two revisions of a single real file, used by t4220-diff-hunks.sh to
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exercise a "trim-divergent" blob pair: one whose diff hunk counts change
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with the amount of context, so the trimmed and untrimmed results
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disagree.
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They are two versions of git's own t/t6002-rev-list-bisect.sh, taken from
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git.git history around:
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090af9957c ("t6002: fix use of `expr` with `set -e`",
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Patrick Steinhardt, 2026-04-21)
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which rewrites `$(expr ...)` arithmetic as `$((...))` and reformats a few
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test_expect_success blocks.
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trim-divergent-old = 090af9957c^:t/t6002-rev-list-bisect.sh (blob daa009c9a1)
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trim-divergent-new = 090af9957c :t/t6002-rev-list-bisect.sh (blob f2de40b5ed)
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To regenerate them from any git.git checkout:
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git show 090af9957c^:t/t6002-rev-list-bisect.sh >trim-divergent-old
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git show 090af9957c:t/t6002-rev-list-bisect.sh >trim-divergent-new
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Why this pair
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-------------
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The diff-hunks store records only "trim-stable" pairs: those whose hunks
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are identical whether or not xdiff trims the common head and tail (which
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it does at zero context, in trim_common_tail). This pair is deliberately
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NOT trim-stable:
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diff -U0 reports 9 added / 6 deleted
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diff -U3 reports 10 added / 7 deleted
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Because the counts diverge with context, the writer must refuse to record
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this pair and every command must recompute it from the blobs. t4220 uses
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it to prove that the displayed counts stay correct at each context, and
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that a divergent pair is never served from the store. See
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t4220-diff-hunks.sh ("a trim-divergent file is correct at each context"
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and the store-poison test).
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Why not a synthesized fixture
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-----------------------------
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The divergence needs real content that makes xdiff's common-tail trimming
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shift a hunk boundary while the added/deleted balance stays equal. A
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minimal hand-written file that reliably triggers the -U0 vs -U3 count
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disagreement has not been found yet; until one is, this real pair is kept
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verbatim. If you synthesize a smaller equivalent, replace these two files
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and delete this note.
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