delta-find: add a test checking various simple behavior

There are enough work happening in this area that it is worth having a dedicated
test for it. So far we add to small test checking that the "best" parent is
picked as the delta base and that this behavior can be controlled during commit
and unbundle.

tests/test-revlog-delta-find.t

@@ -0,0 +1,193 b''
+==========================================================
+Test various things around delta computation within revlog
+==========================================================
+
+
+basic setup
+-----------
+
+  $ cat << EOF >> $HGRCPATH
+  > [debug]
+  > revlog.debug-delta=yes
+  > EOF
+  $ cat << EOF >> sha256line.py
+  > # a way to quickly produce file of significant size and poorly compressable content.
+  > import hashlib
+  > import sys
+  > for line in sys.stdin:
+  >     print(hashlib.sha256(line.encode('utf8')).hexdigest())
+  > EOF
+
+  $ hg init base-repo
+  $ cd base-repo
+
+create a "large" file
+
+  $ $TESTDIR/seq.py 1000 | $PYTHON $TESTTMP/sha256line.py > my-file.txt
+  $ hg add my-file.txt
+  $ hg commit -m initial-commit
+  DBG-DELTAS: FILELOG:my-file.txt: rev=0: delta-base=0 * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+
+Add more change at the end of the file
+
+  $ $TESTDIR/seq.py 1001 1200 | $PYTHON $TESTTMP/sha256line.py >> my-file.txt
+  $ hg commit -m "large-change"
+  DBG-DELTAS: FILELOG:my-file.txt: rev=1: delta-base=0 * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+
+Add small change at the start
+
+  $ hg up 'desc("initial-commit")' --quiet
+  $ mv my-file.txt foo
+  $ echo "small change at the start" > my-file.txt
+  $ cat foo >> my-file.txt
+  $ rm foo
+  $ hg commit -m "small-change"
+  DBG-DELTAS: FILELOG:my-file.txt: rev=2: delta-base=0 * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  created new head
+
+
+  $ hg log -r 'head()' -T '{node}\n' >> ../base-heads.nodes
+  $ hg log -r 'desc("initial-commit")' -T '{node}\n' >> ../initial.node
+  $ hg log -r 'desc("small-change")' -T '{node}\n' >> ../small.node
+  $ hg log -r 'desc("large-change")' -T '{node}\n' >> ../large.node
+  $ cd ..
+
+Check delta find policy and result for merge on commit
+======================================================
+
+Check that delta of merge pick best of the two parents
+------------------------------------------------------
+
+As we check against both parents, the one with the largest change should
+produce the smallest delta and be picked.
+
+  $ hg clone base-repo test-parents --quiet
+  $ hg -R test-parents update 'nodefromfile("small.node")' --quiet
+  $ hg -R test-parents merge 'nodefromfile("large.node")' --quiet
+
+The delta base is the "large" revision as it produce a smaller delta.
+
+  $ hg -R test-parents commit -m "merge from small change"
+  DBG-DELTAS: FILELOG:my-file.txt: rev=3: delta-base=1 * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+
+Check that the behavior tested above can we disabled
+----------------------------------------------------
+
+We disable the checking of both parent at the same time. The `small` change,
+that produce a less optimal delta, should be picked first as it is "closer" to
+the new commit.
+
+  $ hg clone base-repo test-no-parents --quiet
+  $ hg -R test-no-parents update 'nodefromfile("small.node")' --quiet
+  $ hg -R test-no-parents merge 'nodefromfile("large.node")' --quiet
+
+The delta base is the "large" revision as it produce a smaller delta.
+
+  $ hg -R test-no-parents commit -m "merge from small change" \
+  > --config storage.revlog.optimize-delta-parent-choice=no
+  DBG-DELTAS: FILELOG:my-file.txt: rev=3: delta-base=2 * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+
+
+Check delta-find policy and result when unbundling
+==================================================
+
+Build a bundle with all delta built against p1
+
+  $ hg bundle -R test-parents --all --config devel.bundle.delta=p1 all-p1.hg
+  4 changesets found
+
+Default policy of trusting delta from the bundle
+------------------------------------------------
+
+Keeping the `p1` delta used in the bundle is sub-optimal for storage, but
+strusting in-bundle delta is faster to apply.
+
+  $ hg init bundle-default
+  $ hg -R bundle-default unbundle all-p1.hg --quiet
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=0: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=1: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=2: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=3: delta-base=2 * (glob)
+
+(confirm the file revision are in the same order, 2 should be smaller than 1)
+
+  $ hg -R bundle-default debugdata my-file.txt 2 | wc -l
+  \s*1001 (re)
+  $ hg -R bundle-default debugdata my-file.txt 1 | wc -l
+  \s*1200 (re)
+
+explicitly enabled
+------------------
+
+Keeping the `p1` delta used in the bundle is sub-optimal for storage, but
+strusting in-bundle delta is faster to apply.
+
+  $ hg init bundle-reuse-enabled
+  $ hg -R bundle-reuse-enabled unbundle all-p1.hg --quiet \
+  > --config storage.revlog.reuse-external-delta-parent=yes
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=0: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=1: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=2: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=3: delta-base=2 * (glob)
+
+(confirm the file revision are in the same order, 2 should be smaller than 1)
+
+  $ hg -R bundle-reuse-enabled debugdata my-file.txt 2 | wc -l
+  \s*1001 (re)
+  $ hg -R bundle-reuse-enabled debugdata my-file.txt 1 | wc -l
+  \s*1200 (re)
+
+explicitly disabled
+-------------------
+
+Not reusing the delta-base from the parent means we the delta will be made
+against the "best" parent. (so not the same as the previous two)
+
+  $ hg init bundle-reuse-disabled
+  $ hg -R bundle-reuse-disabled unbundle all-p1.hg --quiet \
+  > --config storage.revlog.reuse-external-delta-parent=no
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: CHANGELOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: MANIFESTLOG: * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=0: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=1: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=2: delta-base=0 * (glob)
+  DBG-DELTAS: FILELOG:my-file.txt: rev=3: delta-base=1 * (glob)
+
+(confirm the file revision are in the same order, 2 should be smaller than 1)
+
+  $ hg -R bundle-reuse-disabled debugdata my-file.txt 2 | wc -l
+  \s*1001 (re)
+  $ hg -R bundle-reuse-disabled debugdata my-file.txt 1 | wc -l
+  \s*1200 (re)