What's cooking (2020/06 #02)

todo
Junio C Hamano 2020-06-10 16:35:25 -07:00
parent a11b47e3ec
commit 210b27a8a3
1 changed files with 247 additions and 272 deletions

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@ -1,10 +1,10 @@
To: git@vger.kernel.org
Bcc: lwn@lwn.net
Subject: What's cooking in git.git (Jun 2020, #01; Wed, 3)
X-master-at: 20514004ddf1a3528de8933bc32f284e175e1012
X-next-at: ba653c62daa4884fe39d46cecbbcf7d8c13e7b61
Subject: What's cooking in git.git (Jun 2020, #02; Wed, 10)
X-master-at: 0313f36c6ebecb3bffe6f15cf25a4883100f0214
X-next-at: abb59f83a216876869f6c88d32485dc740ada78d

What's cooking in git.git (Jun 2020, #01; Wed, 3)
What's cooking in git.git (Jun 2020, #02; Wed, 10)
--------------------------------------------------

Here are the topics that have been cooking. Commits prefixed with
@ -12,27 +12,7 @@ Here are the topics that have been cooking. Commits prefixed with
'+' are in 'next'. The ones marked with '.' do not appear in any of
the integration branches, but I am still holding onto them.

Git 2.27 has been tagged, and the first batch of topics (including
the "throw protocol v2 to the experimental group of features" thing)
have been merged to the 'master' branch. I'm planning to rewind the
tip of 'next' in a not-so-distant future.

Seeing a handful of regression reports [*] immediately after a
feature release is made gives me a mixed feeling: people are eager
enough to help by reporting issues they encounter, but there are not
enough people who are eager enough to help by testing the tip of
'master' before the release. Are there things we can do to help
them become early adopters so that they do not have to scramble
after the release?

* sparse-checkout
cf. <CAD3+_6CUX0RPr-dgfUnfGDNNfqu80SYCskioYnu=MS6aJv2dEQ@mail.gmail.com>

* untracked with pathspec
cf. <CAJmdR_pG74x0Zn43MSm7zXNcoitqjjOy+WnhyGBW+oFjVFLbRQ@mail.gmail.com>

* shallow point adjustment
cf. <20200603034213.GB253041@google.com>
The tip of 'next' has been rewound and rebuilt.

You can find the changes described here in the integration branches
of the repositories listed at
@ -42,119 +22,244 @@ of the repositories listed at
--------------------------------------------------
[Graduated to "master"]

* an/merge-single-strategy-optim (2020-05-19) 1 commit
(merged to 'next' on 2020-05-20 at 8d5cacc8d1)
+ merge: optimization to skip evaluate_result for single strategy
* bc/filter-process (2020-05-21) 2 commits
(merged to 'next' on 2020-05-24 at 3d51328096)
+ t2060: add a test for switch with --orphan and --discard-changes
+ builtin/checkout: simplify metadata initialization

Code optimization for a common case.
Code simplification and test coverage enhancement.


* bk/p4-prepare-p4-only-fix (2020-05-12) 1 commit
(merged to 'next' on 2020-05-24 at c1b4644b04)
+ git-p4.py: fix --prepare-p4-only error with multiple commits
* cb/bisect-helper-parser-fix (2020-05-24) 1 commit
(merged to 'next' on 2020-05-24 at d30e10fa86)
+ bisect--helper: avoid segfault with bad syntax in `start --term-*`

The "--prepare-p4-only" option is supposed to stop after replaying
one changeset, but kept going (by mistake?)
cf. <CAE5ih797YYxsR2H0TA65w9W-1jF4jQLayja_nGjQMGtc=PB6Jw@mail.gmail.com>
The code to parse "git bisect start" command line was lax in
validating the arguments.


* cb/t5608-cleanup (2020-05-24) 1 commit
(merged to 'next' on 2020-05-24 at 2bfa581890)
+ t5608: avoid say() and use "skip_all" instead for consistency
* cb/t4210-illseq-auto-detect (2020-05-18) 2 commits
(merged to 'next' on 2020-05-24 at c03b4095fa)
+ t4210: detect REG_ILLSEQ dynamically and skip affected tests
+ t/helper: teach test-regex to report pattern errors (like REG_ILLSEQ)

Test fixup.
As FreeBSD is not the only platform whose regexp library reports
a REG_ILLSEQ error when fed invalid UTF-8, add logic to detect that
automatically and skip the affected tests.


* en/fast-import-looser-date (2020-05-31) 1 commit
(merged to 'next' on 2020-05-31 at 49de9c07c5)
+ fast-import: add new --date-format=raw-permissive format
* cc/upload-pack-data (2020-05-18) 13 commits
(merged to 'next' on 2020-05-29 at 66008d9209)
+ upload-pack: use upload_pack_data fields in receive_needs()
+ upload-pack: pass upload_pack_data to create_pack_file()
+ upload-pack: remove static variable 'stateless_rpc'
+ upload-pack: pass upload_pack_data to check_non_tip()
+ upload-pack: pass upload_pack_data to send_ref()
+ upload-pack: move symref to upload_pack_data
+ upload-pack: use upload_pack_data writer in receive_needs()
+ upload-pack: pass upload_pack_data to receive_needs()
+ upload-pack: pass upload_pack_data to get_common_commits()
+ upload-pack: use 'struct upload_pack_data' in upload_pack()
+ upload-pack: move 'struct upload_pack_data' around
+ upload-pack: move {want,have}_obj to upload_pack_data
+ upload-pack: remove unused 'wants' from upload_pack_data
(this branch is used by cc/upload-pack-data-2.)

Some repositories in the wild have commits that record nonsense
committer timezone (e.g. rails.git); "git fast-import" learned an
option to pass these nonsense timestamps intact to allow recreating
existing repositories as-is.
Code clean-up.


* jn/experimental-opts-into-proto-v2 (2020-05-21) 1 commit
(merged to 'next' on 2020-05-24 at 53cd664dfe)
+ config: let feature.experimental imply protocol.version=2
* dl/remote-curl-deadlock-fix (2020-05-24) 7 commits
(merged to 'next' on 2020-05-26 at 072714ca7f)
+ stateless-connect: send response end packet
+ pkt-line: define PACKET_READ_RESPONSE_END
+ remote-curl: error on incomplete packet
+ pkt-line: extern packet_length()
+ transport: extract common fetch_pack() call
+ remote-curl: remove label indentation
+ remote-curl: fix typo

"feature.experimental" configuration variable is to let volunteers
easily opt into a set of newer features, which use of the v2
transport protocol is now a part of.
On-the-wire protocol v2 easily falls into a deadlock between the
remote-curl helper and the fetch-pack process when the server side
prematurely throws an error and disconnects. The communication has
been updated to make it more robust.


* jx/pkt-line-doc-count-fix (2020-05-21) 1 commit
(merged to 'next' on 2020-05-24 at 7115240db4)
+ doc: fix wrong 4-byte length of pkt-line message
* ds/line-log-on-bloom (2020-05-11) 5 commits
(merged to 'next' on 2020-05-11 at 046d49d455)
+ line-log: integrate with changed-path Bloom filters
+ line-log: try to use generation number-based topo-ordering
+ line-log: more responsive, incremental 'git log -L'
+ t4211-line-log: add tests for parent oids
+ line-log: remove unused fields from 'struct line_log_data'
(this branch is used by sg/commit-graph-cleanups.)

Docfix.
"git log -L..." now takes advantage of the "which paths are touched
by this commit?" info stored in the commit-graph system.


* la/diff-relative-config (2020-05-24) 1 commit
(merged to 'next' on 2020-05-26 at b4604e6abc)
+ diff: add config option relative
* es/bugreport-shell (2020-05-12) 2 commits
(merged to 'next' on 2020-05-24 at 79c5c8308b)
+ bugreport: include user interactive shell
+ help: add shell-path to --build-options

The commands in the "diff" family learned to honor "diff.relative"
configuration variable.
"git bugreport" learns to report what shell is in use.
We may want to learn more details than just the path, but
that can come later.
cf. <20200512235924.GC6605@camp.crustytoothpaste.net>


* lo/sparse-universal-zero-init (2020-05-24) 1 commit
(merged to 'next' on 2020-05-24 at 1f4ea6b348)
+ sparse: allow '{ 0 }' to be used without warnings
* js/checkout-p-new-file (2020-05-27) 1 commit
(merged to 'next' on 2020-05-31 at 017c325bf6)
+ checkout -p: handle new files correctly

We've adopted a convention that any on-stack structure can be
initialized to have zero values in all fields with "= { 0 }", even
when the first field happens to be a pointer, but sparse complained
that a null pointer should be spelled NULL for a long time. Start
using -Wno-universal-initializer option to squelch it.
"git checkout -p" did not handle a newly added path at all.


* mt/zsh-completion-optim (2020-05-28) 1 commit
(merged to 'next' on 2020-05-31 at f5d02a5498)
+ completion: use native ZSH array pattern matching
* jt/curl-verbose-on-trace-curl (2020-05-11) 2 commits
(merged to 'next' on 2020-05-11 at 814e31b9d4)
+ http, imap-send: stop using CURLOPT_VERBOSE
+ t5551: test that GIT_TRACE_CURL redacts password
(this branch is used by jt/redact-all-cookies.)

Command line completion (incontrib/) update.
Rewrite support for GIT_CURL_VERBOSE in terms of GIT_TRACE_CURL.


* rs/checkout-b-track-error (2020-05-24) 2 commits
(merged to 'next' on 2020-05-26 at 9220e43203)
+ checkout: improve error messages for -b with extra argument
+ checkout: add tests for -b and --track
* rs/fsck-duplicate-names-in-trees (2020-05-21) 4 commits
(merged to 'next' on 2020-05-24 at 6e1d6ba087)
+ fsck: detect more in-tree d/f conflicts
+ t1450: demonstrate undetected in-tree d/f conflict
+ t1450: increase test coverage of in-tree d/f detection
+ fsck: fix a typo in a comment

The error message from "git checkout -b foo -t bar baz" was
confusing.
The check in "git fsck" to ensure that the tree objects are sorted
still had corner cases it missed unsorted entries.


* tb/commit-graph-no-check-oids (2020-05-18) 8 commits
(merged to 'next' on 2020-05-24 at 72bd1063ca)
+ commit-graph: drop COMMIT_GRAPH_WRITE_CHECK_OIDS flag
+ t5318: reorder test below 'graph_read_expect'
+ commit-graph.c: simplify 'fill_oids_from_commits'
+ builtin/commit-graph.c: dereference tags in builtin
+ builtin/commit-graph.c: extract 'read_one_commit()'
+ commit-graph.c: peel refs in 'add_ref_to_set'
+ commit-graph.c: show progress of finding reachable commits
+ commit-graph.c: extract 'refs_cb_data'

Clean-up the commit-graph codepath.


* vs/complete-stash-show-p-fix (2020-05-21) 1 commit
(merged to 'next' on 2020-05-24 at fcbff29a0f)
+ completion: don't override given stash subcommand with -p

The command line completion script (in contrib/) tried to complete
"git stash -p" as if it were "git stash push -p", but it was too
aggressive and also affected "git stash show -p", which has been
corrected.

--------------------------------------------------
[New Topics]

* jk/diff-memuse-optim-with-stat-unmatch (2020-06-02) 1 commit
- diff: discard blob data from stat-unmatched pairs
* en/sparse-checkout (2020-06-05) 1 commit
- sparse-checkout: avoid staging deletions of all files

Reduce memory usage during "diff --quiet" in a worktree with too
many stat-unmatched paths.
The behaviour of "sparse-checkout" in the state "git clone
--no-checkout" left was changed accidentally in 2.27, which has
been corrected.

Will merge to 'next'.


* js/reflog-anonymize-for-clone-and-fetch (2020-06-02) 1 commit
- clone/fetch: anonymize URLs in the reflog
* js/msvc-build-fix (2020-06-04) 1 commit
- msvc: fix "REG_STARTEND" issue

The reflog entries for "git clone" and "git fetch" did not
anonymize the URL they operated on.
Workaround breakage in MSVC build, where "curl-config --cflags"
gives settings appropriate for GCC build.

Will merge to 'next'.


* tb/t5318-cleanup (2020-06-02) 2 commits
- t5318: test that '--stdin-commits' respects '--[no-]progress'
- t5318: use 'test_must_be_empty'
* en/do-match-pathspec-fix (2020-06-05) 1 commit
- dir: fix treatment of negated pathspecs

Use of negative pathspec, while collecting paths including
untracked ones in the working tree, was broken.

Will merge to 'next'.


* jt/redact-all-cookies (2020-06-05) 1 commit
- http: redact all cookies, teach GIT_TRACE_REDACT=0

The interface to redact sensitive information in the trace output
has been simplified.

Will merge to 'next'.


* dl/python-2.7-is-the-floor-version (2020-06-08) 1 commit
- CodingGuidelines: specify Python 2.7 is the oldest version

Document that we do not support Python 2.6 or older.

Will merge to 'next'.


* dl/t-readme-spell-git-correctly (2020-06-08) 1 commit
- t/README: avoid poor-man's small caps GIT

Doc updates.

Will merge to 'next'.


* es/advertise-contribution-doc (2020-06-08) 1 commit
- docs: mention MyFirstContribution in more places

Doc updates.

Will merge to 'next'.


* es/worktree-duplicate-paths (2020-06-10) 7 commits
- worktree: make "move" refuse to move atop missing registered worktree
- worktree: generalize candidate worktree path validation
- worktree: prune linked worktree referencing main worktree path
- worktree: prune duplicate entries referencing same worktree path
- worktree: make high-level pruning re-usable
- worktree: give "should be pruned?" function more meaningful name
- worktree: factor out repeated string literal

The same worktree directory must be registered only once, but
"git worktree move" allowed this invariant to be violated, which
has been corrected.

Will merge to 'next'.


* js/fuzz-commit-graph-leakfix (2020-06-08) 1 commit
- fuzz-commit-graph: properly free graph struct

Leakfix.

Will merge to 'next'.


* sg/commit-graph-cleanups (2020-06-08) 10 commits
- commit-graph: simplify write_commit_graph_file() #2
- commit-graph: simplify write_commit_graph_file() #1
- commit-graph: simplify parse_commit_graph() #2
- commit-graph: simplify parse_commit_graph() #1
- commit-graph: clean up #includes
- diff.h: drop diff_tree_oid() & friends' return value
- commit-slab: add a function to deep free entries on the slab
- commit-graph-format.txt: all multi-byte numbers are in network byte order
- commit-graph: fix parsing the Chunk Lookup table
- tree-walk.c: don't match submodule entries for 'submod/anything'

Code cleanup.

Almost there.
cf. <20200602180403.GA4791@szeder.dev>

--------------------------------------------------
[Stalled]

@ -216,8 +321,34 @@ of the repositories listed at
--------------------------------------------------
[Cooking]

* cc/upload-pack-data-2 (2020-06-02) 14 commits
- fixup! upload-pack: change multi_ack to an enum
* jk/diff-memuse-optim-with-stat-unmatch (2020-06-02) 1 commit
- diff: discard blob data from stat-unmatched pairs

Reduce memory usage during "diff --quiet" in a worktree with too
many stat-unmatched paths.

Will merge to 'next'.


* js/reflog-anonymize-for-clone-and-fetch (2020-06-04) 1 commit
- clone/fetch: anonymize URLs in the reflog

The reflog entries for "git clone" and "git fetch" did not
anonymize the URL they operated on.

Will merge to 'next'.


* tb/t5318-cleanup (2020-06-04) 2 commits
- t5318: test that '--stdin-commits' respects '--[no-]progress'
- t5318: use 'test_must_be_empty'

Code cleanup.

Will merge to 'next'.


* cc/upload-pack-data-2 (2020-06-04) 13 commits
- upload-pack: move pack_objects_hook to upload_pack_data
- upload-pack: move allow_sideband_all to upload_pack_data
- upload-pack: move allow_ref_in_want to upload_pack_data
@ -231,29 +362,22 @@ of the repositories listed at
- upload-pack: move static vars to upload_pack_data
- upload-pack: annotate upload_pack_data fields
- upload-pack: actually use some upload_pack_data bitfields
(this branch uses cc/upload-pack-data.)

Further code clean-up.

Almost there.
Will merge to 'next'.


* js/checkout-p-new-file (2020-05-27) 1 commit
(merged to 'next' on 2020-05-31 at 017c325bf6)
+ checkout -p: handle new files correctly

"git checkout -p" did not handle a newly added path at all.

Will merge to 'master'.


* xl/upgrade-repo-format (2020-05-29) 1 commit
* xl/upgrade-repo-format (2020-06-05) 4 commits
- check_repository_format_gently(): refuse extensions for old repositories
- sparse-checkout: upgrade repository to version 1 when enabling extension
- fetch: allow adding a filter after initial clone
- repository: add a helper function to perform repository format upgrade

Allow runtime upgrade of the repository format version, which needs
to be done carefully.

Almost there.
Almost there. It does not seem to play well with hn/reftable


* jk/complete-git-switch (2020-05-28) 16 commits
@ -277,6 +401,8 @@ of the repositories listed at
The command line completion (in contrib/) learned to complete
options that the "git switch" command takes.

Is this ready?


* en/sparse-with-submodule-doc (2020-05-25) 1 commit
- git-sparse-checkout: clarify interactions with submodules
@ -286,39 +412,6 @@ of the repositories listed at
Needs review.


* bc/filter-process (2020-05-21) 2 commits
(merged to 'next' on 2020-05-24 at 3d51328096)
+ t2060: add a test for switch with --orphan and --discard-changes
+ builtin/checkout: simplify metadata initialization

Code simplification and test coverage enhancement.

Will merge to 'master'.


* cb/bisect-helper-parser-fix (2020-05-24) 1 commit
(merged to 'next' on 2020-05-24 at d30e10fa86)
+ bisect--helper: avoid segfault with bad syntax in `start --term-*`

The code to parse "git bisect start" command line was lax in
validating the arguments.

Will merge to 'master'.


* rs/fsck-duplicate-names-in-trees (2020-05-21) 4 commits
(merged to 'next' on 2020-05-24 at 6e1d6ba087)
+ fsck: detect more in-tree d/f conflicts
+ t1450: demonstrate undetected in-tree d/f conflict
+ t1450: increase test coverage of in-tree d/f detection
+ fsck: fix a typo in a comment

The check in "git fsck" to ensure that the tree objects are sorted
still had corner cases it missed unsorted entries.

Will merge to 'master'.


* ss/submodule-set-branch-in-c (2020-06-02) 1 commit
- submodule: port subcommand 'set-branch' from shell to C

@ -330,23 +423,13 @@ of the repositories listed at
cf. <1b851e49-3bb1-3b59-7f24-b903c5514391@gmail.com>


* vs/complete-stash-show-p-fix (2020-05-21) 1 commit
(merged to 'next' on 2020-05-24 at fcbff29a0f)
+ completion: don't override given stash subcommand with -p

The command line completion script (in contrib/) tried to complete
"git stash -p" as if it were "git stash push -p", but it was too
aggressive and also affected "git stash show -p", which has been
corrected.

Will merge to 'master'.


* es/config-hooks (2020-05-21) 4 commits
. hook: add --porcelain to list command
. hook: add list command
. hook: scaffolding for git-hook subcommand
. doc: propose hooks managed by the config
- hook: add --porcelain to list command
- hook: add list command
- hook: scaffolding for git-hook subcommand
- doc: propose hooks managed by the config

The "hooks defined in config" topic.


* pw/rebase-i-more-options (2020-05-27) 5 commits
@ -358,72 +441,10 @@ of the repositories listed at

"git rebase -i" learns a bit more options.

Not quite
Not quite.
cf. <nycvar.QRO.7.76.6.2005290437350.56@tvgsbejvaqbjf.bet>


* cc/upload-pack-data (2020-05-18) 13 commits
(merged to 'next' on 2020-05-29 at 66008d9209)
+ upload-pack: use upload_pack_data fields in receive_needs()
+ upload-pack: pass upload_pack_data to create_pack_file()
+ upload-pack: remove static variable 'stateless_rpc'
+ upload-pack: pass upload_pack_data to check_non_tip()
+ upload-pack: pass upload_pack_data to send_ref()
+ upload-pack: move symref to upload_pack_data
+ upload-pack: use upload_pack_data writer in receive_needs()
+ upload-pack: pass upload_pack_data to receive_needs()
+ upload-pack: pass upload_pack_data to get_common_commits()
+ upload-pack: use 'struct upload_pack_data' in upload_pack()
+ upload-pack: move 'struct upload_pack_data' around
+ upload-pack: move {want,have}_obj to upload_pack_data
+ upload-pack: remove unused 'wants' from upload_pack_data
(this branch is used by cc/upload-pack-data-2.)

Code clean-up.

Will merge to 'master'.


* dl/remote-curl-deadlock-fix (2020-05-24) 7 commits
(merged to 'next' on 2020-05-26 at 072714ca7f)
+ stateless-connect: send response end packet
+ pkt-line: define PACKET_READ_RESPONSE_END
+ remote-curl: error on incomplete packet
+ pkt-line: extern packet_length()
+ transport: extract common fetch_pack() call
+ remote-curl: remove label indentation
+ remote-curl: fix typo

On-the-wire protocol v2 easily falls into a deadlock between the
remote-curl helper and the fetch-pack process when the server side
prematurely throws an error and disconnects. The communication has
been updated to make it more robust.

Will merge to 'master'.


* cb/t4210-illseq-auto-detect (2020-05-18) 2 commits
(merged to 'next' on 2020-05-24 at c03b4095fa)
+ t4210: detect REG_ILLSEQ dynamically and skip affected tests
+ t/helper: teach test-regex to report pattern errors (like REG_ILLSEQ)

As FreeBSD is not the only platform whose regexp library reports
a REG_ILLSEQ error when fed invalid UTF-8, add logic to detect that
automatically and skip the affected tests.

Will merge to 'master'.


* jt/curl-verbose-on-trace-curl (2020-05-11) 2 commits
(merged to 'next' on 2020-05-11 at 814e31b9d4)
+ http, imap-send: stop using CURLOPT_VERBOSE
+ t5551: test that GIT_TRACE_CURL redacts password

Rewrite support for GIT_CURL_VERBOSE in terms of GIT_TRACE_CURL.

Expecting further work on optionally disabling redacting authinfo


* mt/grep-sparse-checkout (2020-06-02) 6 commits
- git.c: fix sparse warning
- config: add setting to ignore sparsity patterns in some cmds
@ -489,49 +510,6 @@ of the repositories listed at
SHA-256 migration work continues.


* es/bugreport-shell (2020-05-12) 2 commits
(merged to 'next' on 2020-05-24 at 79c5c8308b)
+ bugreport: include user interactive shell
+ help: add shell-path to --build-options

"git bugreport" learns to report what shell is in use.

Will merge to 'master'.
We may want to learn more details than just the path, but
that can come later.
cf. <20200512235924.GC6605@camp.crustytoothpaste.net>


* ds/line-log-on-bloom (2020-05-11) 5 commits
(merged to 'next' on 2020-05-11 at 046d49d455)
+ line-log: integrate with changed-path Bloom filters
+ line-log: try to use generation number-based topo-ordering
+ line-log: more responsive, incremental 'git log -L'
+ t4211-line-log: add tests for parent oids
+ line-log: remove unused fields from 'struct line_log_data'

"git log -L..." now takes advantage of the "which paths are touched
by this commit?" info stored in the commit-graph system.

Will merge to 'master'.


* tb/commit-graph-no-check-oids (2020-05-18) 8 commits
(merged to 'next' on 2020-05-24 at 72bd1063ca)
+ commit-graph: drop COMMIT_GRAPH_WRITE_CHECK_OIDS flag
+ t5318: reorder test below 'graph_read_expect'
+ commit-graph.c: simplify 'fill_oids_from_commits'
+ builtin/commit-graph.c: dereference tags in builtin
+ builtin/commit-graph.c: extract 'read_one_commit()'
+ commit-graph.c: peel refs in 'add_ref_to_set'
+ commit-graph.c: show progress of finding reachable commits
+ commit-graph.c: extract 'refs_cb_data'

Clean-up the commit-graph codepath.

Will merge to 'master'.


* jx/proc-receive-hook (2020-05-18) 11 commits
- doc: add documentation for the proc-receive hook
- transport: parse report options for tracking refs
@ -551,10 +529,8 @@ of the repositories listed at
Needs review.


* hn/refs-cleanup (2020-05-27) 7 commits
(merged to 'next' on 2020-05-27 at aada2199e1)
+ reftable doc: use link: and urlencode to avoid dead links
(merged to 'next' on 2020-05-24 at dd9b665698)
* hn/refs-cleanup (2020-06-09) 6 commits
(merged to 'next' on 2020-06-09 at abb59f83a2)
+ reftable: define version 2 of the spec to accomodate SHA256
+ reftable: clarify how empty tables should be written
+ reftable: file format documentation
@ -566,15 +542,14 @@ of the repositories listed at
Preliminary clean-ups around refs API, plus file format
specification documentation for the reftable backend.

Will merge to 'master' after squashing the fix in.
We probably would want to squash the fix at the tip to an earlier
step when we rewind the 'next' branch.
Will merge to 'master'.


* hn/reftable (2020-05-28) 13 commits
* hn/reftable (2020-06-09) 14 commits
. Add reftable testing infrastructure
. vcxproj: adjust for the reftable changes
. Add GIT_DEBUG_REFS debugging mechanism
. Hookup unittests for the reftable library.
. Reftable support for git-core
. Add reftable library
. Add .gitattributes for the reftable/ directory
@ -592,7 +567,7 @@ of the repositories listed at
has been implemented and integrated for improved performance and
atomicity.

Not quite--does not pass tests by itself.
Does not seem to build from the source.

--------------------------------------------------
[Discarded]