test_i18ngrep corrupt stderr
'
+# have_delta <obj> <expected_base>
+#
+# Note that because this relies on cat-file, it might find _any_ copy of an
+# object in the repository. The caller is responsible for making sure
+# there's only one (e.g., via "repack -ad", or having just fetched a copy).
+have_delta () {
+ echo $2 >expect &&
+ echo $1 | git cat-file --batch-check="%(deltabase)" >actual &&
+ test_cmp expect actual
+}
+
+# Create a state of history with these properties:
+#
+# - refs that allow a client to fetch some new history, while sharing some old
+# history with the server; we use branches delta-reuse-old and
+# delta-reuse-new here
+#
+# - the new history contains an object that is stored on the server as a delta
+# against a base that is in the old history
+#
+# - the base object is not immediately reachable from the tip of the old
+# history; finding it would involve digging down through history we know the
+# other side has
+#
+# This should result in a state where fetching from old->new would not
+# traditionally reuse the on-disk delta (because we'd have to dig to realize
+# that the client has it), but we will do so if bitmaps can tell us cheaply
+# that the other side has it.
+test_expect_success 'set up thin delta-reuse parent' '
+ # This first commit contains the buried base object.
+ test-tool genrandom delta 16384 >file &&
+ git add file &&
+ git commit -m "delta base" &&
+ base=$(git rev-parse --verify HEAD:file) &&
+
+ # These intermediate commits bury the base back in history.
+ # This becomes the "old" state.
+ for i in 1 2 3 4 5
+ do
+ echo $i >file &&
+ git commit -am "intermediate $i" || return 1
+ done &&
+ git branch delta-reuse-old &&
+
+ # And now our new history has a delta against the buried base. Note
+ # that this must be smaller than the original file, since pack-objects
+ # prefers to create deltas from smaller objects to larger.
+ test-tool genrandom delta 16300 >file &&
+ git commit -am "delta result" &&
+ delta=$(git rev-parse --verify HEAD:file) &&
+ git branch delta-reuse-new &&
+
+ # Repack with bitmaps and double check that we have the expected delta
+ # relationship.
+ git repack -adb &&
+ have_delta $delta $base
+'
+
+# Now we can sanity-check the non-bitmap behavior (that the server is not able
+# to reuse the delta). This isn't strictly something we care about, so this
+# test could be scrapped in the future. But it makes sure that the next test is
+# actually triggering the feature we want.
+#
+# Note that our tools for working with on-the-wire "thin" packs are limited. So
+# we actually perform the fetch, retain the resulting pack, and inspect the
+# result.
+test_expect_success 'fetch without bitmaps ignores delta against old base' '
+ test_config pack.usebitmaps false &&
+ test_when_finished "rm -rf client.git" &&
+ git init --bare client.git &&
+ (
+ cd client.git &&
+ git config transfer.unpackLimit 1 &&
+ git fetch .. delta-reuse-old:delta-reuse-old &&
+ git fetch .. delta-reuse-new:delta-reuse-new &&
+ have_delta $delta $ZERO_OID
+ )
+'
+
+# And do the same for the bitmap case, where we do expect to find the delta.
+test_expect_success 'fetch with bitmaps can reuse old base' '
+ test_config pack.usebitmaps true &&
+ test_when_finished "rm -rf client.git" &&
+ git init --bare client.git &&
+ (
+ cd client.git &&
+ git config transfer.unpackLimit 1 &&
+ git fetch .. delta-reuse-old:delta-reuse-old &&
+ git fetch .. delta-reuse-new:delta-reuse-new &&
+ have_delta $delta $base
+ )
+'
+
test_done