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authorLibravatar Jeff King <peff@peff.net>2020-09-30 07:52:40 -0400
committerLibravatar Junio C Hamano <gitster@pobox.com>2020-09-30 13:35:24 -0700
commit957876f17d75b5cd0e94b85d3df843bb1e9ae110 (patch)
tree71222615b3cd83c2268a57622b34278a257a5ad8 /t
parentGit 2.28 (diff)
downloadtgif-957876f17d75b5cd0e94b85d3df843bb1e9ae110.tar.xz
combine-diff: handle --find-object in multitree code path
When doing combined diffs, we have two possible code paths: - a slower one which independently diffs against each parent, applies any filters, and then intersects the resulting paths - a faster one which walks all trees simultaneously When the diff options specify that we must do certain filters, like pickaxe, then we always use the slow path, since the pickaxe code only knows how to handle filepairs, not the n-parent entries generated for combined diffs. But there are two problems with the slow path: 1. It's slow. Running: git rev-list HEAD | git diff-tree --stdin -r -c in git.git takes ~3s on my machine. But adding "--find-object" to that increases it to ~6s, even though find-object itself should incur only a few extra oid comparisons. On linux.git, it's even worse: 35s versus 215s. 2. It doesn't catch all cases where a particular path is interesting. Consider a merge with parent blobs X and Y for a particular path, and end result Z. That should be interesting according to "-c", because the result doesn't match either parent. And it should be interesting even with "--find-object=X", because "X" went away in the merge. But because we perform each pairwise diff independently, this confuses the intersection code. The change from X to Z is still interesting according to --find-object. But in the other parent we went from Y to Z, so the diff appears empty! That causes the intersection code to think that parent didn't change the path, and thus it's not interesting for "-c". This patch fixes both by implementing --find-object for the multitree code. It's a bit unfortunate that we have to duplicate some logic from diffcore-pickaxe, but this is the best we can do for now. In an ideal world, all of the diffcore code would stop thinking about filepairs and start thinking about n-parent sets, and we could use the multitree walk with all of it. Until then, there are some leftover warts: - other pickaxe operations, like -S or -G, still suffer from both problems. These would be hard to adapt because they rely on having a diff_filespec() for each path to look at content. And we'd need to define what an n-way "change" means in each case (probably easy for "-S", which can compare counts, but not so clear for -G, which is about grepping diffs). - other options besides --find-object may cause us to use the slow pairwise path, in which case we'll go back to producing a different (wrong) answer for the X/Y/Z case above. We may be able to hack around these, but I think the ultimate solution will be a larger rewrite of the diffcore code. For now, this patch improves one specific case but leaves the rest. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 't')
-rwxr-xr-xt/t4064-diff-oidfind.sh55
1 files changed, 55 insertions, 0 deletions
diff --git a/t/t4064-diff-oidfind.sh b/t/t4064-diff-oidfind.sh
index 3bdf317af8..6d8c8986fc 100755
--- a/t/t4064-diff-oidfind.sh
+++ b/t/t4064-diff-oidfind.sh
@@ -65,4 +65,59 @@ test_expect_success 'find a submodule' '
test_cmp expect actual
'
+test_expect_success 'set up merge tests' '
+ test_commit base &&
+
+ git checkout -b boring base^ &&
+ echo boring >file &&
+ git add file &&
+ git commit -m boring &&
+
+ git checkout -b interesting base^ &&
+ echo interesting >file &&
+ git add file &&
+ git commit -m interesting &&
+
+ blob=$(git rev-parse interesting:file)
+'
+
+test_expect_success 'detect merge which introduces blob' '
+ git checkout -B merge base &&
+ git merge --no-commit boring &&
+ echo interesting >file &&
+ git commit -am "introduce blob" &&
+ git diff-tree --format=%s --find-object=$blob -c --name-status HEAD >actual &&
+ cat >expect <<-\EOF &&
+ introduce blob
+
+ AM file
+ EOF
+ test_cmp expect actual
+'
+
+test_expect_success 'detect merge which removes blob' '
+ git checkout -B merge interesting &&
+ git merge --no-commit base &&
+ echo boring >file &&
+ git commit -am "remove blob" &&
+ git diff-tree --format=%s --find-object=$blob -c --name-status HEAD >actual &&
+ cat >expect <<-\EOF &&
+ remove blob
+
+ MA file
+ EOF
+ test_cmp expect actual
+'
+
+test_expect_success 'do not detect merge that does not touch blob' '
+ git checkout -B merge interesting &&
+ git merge -m "untouched blob" base &&
+ git diff-tree --format=%s --find-object=$blob -c --name-status HEAD >actual &&
+ cat >expect <<-\EOF &&
+ untouched blob
+
+ EOF
+ test_cmp expect actual
+'
+
test_done