[llvm-dev] New LLVM git repository conversion prototype
David Jones via llvm-dev
llvm-dev at lists.llvm.org
Fri Nov 16 14:46:32 PST 2018
Hi James,
I've started working with the prototype layout in context of Google's
internal infrastructure. With deep apologies, I have a (very late, I know)
pair of requests that have only recently solidified for me.
1. Could you add annotated tags after the cut point of each release? (I
think this would probably be easy.)
2. Could you mark branch/tag operations somehow other than a annotated tag
on master? (This seems less trivial, but my reasoning is below.)
The overall goal is for `git describe` to give a reasonable default output.
Reasoning for request #1:
Example: add a tag after the cut point of the 7.0 release:
$ git log --oneline $(git merge-base HEAD origin/release_70)..HEAD | tail -1
63297479398 Bump the trunk version to 8.0.0svn
$ git tag -m 'Begin development of 8.0.0.' '8.0.0svn' 63297479398
Then, `git describe` can give a useful result that would be stable(-ish
[*]):
$ git describe --match=\*svn
8.0.0svn-7878-gfdb08034fd8
([*] Subject to the normal caveat for git-describe: the trailing short hash
may become non-unique over time. This is mentioned in the git help.)
Again, I think these tags could probably be added later, but it would be
nice to have a single source of truth (especially since the tag annotation
is itself a commit).
I think we could also probably come up with better than than '8.0.0svn';
although whatever the choice, they probably need to be suitable for
--match, because...
Reasoning for request #2:
Since many other branch/tag operations are stored as annotated tags, they
are currently used by git-describe:
$ git describe
google/stable/2018-10-04-3473-gfdb08034fd8
This doesn't seem as generally useful to me as the release-cut based
revisions... describing a commit as "the 7878th of 8.0.0 development" seems
more generally helpful than saying "the 3473rd after a google/stable
release."
A very similar approach might be to drop the existing annotated tags, and
add the unchanged branches as no-change commits (i.e., the equivalent of
`git commit --allow-empty`), with a lightweight tag.
Unfortunately, this seems (to me) to be harder to fix than #1. The "similar
approach" seems like it could be added safely without recreating the entire
history, but it seems like this would need to be done before folks start
depending on the existing tags.
(Of course, it's possible I've completely missed something obvious or
somehow fouled up my clone of the repo, and this is already supposed to
work... let me know if I've missed something, or if you have a better
approach.)
On Fri, Nov 16, 2018 at 1:11 PM James Y Knight via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Yes, I believe all the known issues are resolved and that we're ready to
> go, whenever the other thread (on whether to abandon this monorepo, and
> zipper-commit the existing gitrepositories) is concluded.
>
> On Thu, Nov 15, 2018 at 4:09 PM Tom Stellard <tstellar at redhat.com> wrote:
>
>> On 10/11/2018 03:27 PM, James Y Knight via llvm-dev wrote:
>> > TLDR: https://github.com/llvm-git-prototype/ exists as a read-only
>> mirror of SVN, and is being updated continuously with a script running on
>> an llvm-project AWS VM.
>> >
>>
>> Hi James,
>>
>> What is the current status of the monorepo, have you resolved all the
>> known issues with the history? Are there any other changes that need
>> to be made before it can be finalized?
>>
>> -Tom
>>
>> > Let me know what you think.
>> >
>> > I had meant to get this prototype finalized 6 months ago, and I must
>> apologize for the delay. I hope this is close to final for what we want our
>> git repository to look like, and that we can move forward with the
>> remainder of the work to convert to git.
>> >
>> > At this point, there's no guarantee that the repository won't be
>> rebuilt from scratch with new hashes, if some problem is discovered which
>> requires changing something way back in history. But I hope we're now close
>> to being able to declare a conversion final -- and let people start
>> depending on the hashes being stable.
>> >
>> > This conversion uses the "flat monorepo" layout, like the previous
>> existing git monorepo, and as discussed previously. The process generating
>> it is different, which allows a more faithful conversion, including
>> branches. I've also converted a bunch of the auxiliary repositories.
>> >
>> > I would request that other people help take charge of the remainder of
>> the work. Most importantly -- making a plan for implementing the *rest* of
>> the migration. We have https://llvm.org/docs/Proposals/GitHubMove.html,
>> but I think it'll need significant fleshing out and updating. I'm happy to
>> assist with the rest of the migration, but I'd like to _not_ be primarily
>> responsible for other parts beyond svn->git repository conversion.
>> >
>> > Some things that could be discussed in such a plan:
>> > * Verifying that this conversion is good, what we want, and declaring
>> it final (at which point the hashes can be relied upon not to change).
>> > * Any particular steps wanted here?
>> > * Converting buildbots to use git.
>> > * Phabricator changes?
>> > * How do email notifications get sent for commits?
>> > * Gathering github accounts for all committers, adding them to a
>> github team.
>> > * Deciding upon and announcing a timeline for switching over.
>> > * Proposing, implementing, and testing new workflows for direct git
>> usage:
>> > * Github pull requests instead of (or in addition to?) phabricator?
>> > * Github Protected Branch configuration options?
>> > * E.g. -- direct pushing to git without any restriction, or,
>> require that pull requests be created first?
>> > * Automated Pre-commit testing? Do we setup CI (e.g.
>> travis-ci.org <http://travis-ci.org>) to do some testing on pull
>> requests, to reduce avoidable tree breakages?
>> > * Any other github configuration options that need to be decided
>> upon?
>> > * ....other things I forgot about at the moment...
>> > * Timeline for switchover.
>> >
>> >
>> >
>> > Anyways, what's been done _so far_ is a full SVN->Git repository
>> conversion. This conversion:
>> > * Places the SVN revision number into the commit message, as
>> "llvm-svn=1234"
>> >
>> > * Automatically preserves all branches from the SVN repository (it
>> merges the branches named /$project/branches/$name into a single "$name"
>> branch, attempting, as much as possible, to make the branch-creation
>> commits not look insane).
>> >
>> > * Attempts to convert the svn branches in the "tags" subdir into
>> annotated git tags pointing to the proper commit on the parent branch,
>> where feasible. Sometimes this is impossible, since the "tags" have had
>> modifications after their creation. (They're just branches in SVN, so you
>> can do that, although you shouldn't). If so, they're preserved as a branch
>> named "svntag/$name", instead.
>> >
>> > * Preserves the svn id -> email mapping that was in-use at the time
>> of each SVN commit, as far as is known.
>> >
>> > * Fixes a bunch of -- but not all -- the CVS->SVN conversion errors
>> (due, e.g., to files being renamed directly in the CVS repository).
>> >
>> >
>> >
>> > Most of the SVN directories are migrated into sub-directories inside
>> the main "llvm" mono-repository:
>> > * cfe (renamed to clang in the conversion)
>> > * clang-tools-extra
>> > * compiler-rt
>> > * debuginfo-tests
>> > * dragonegg (also "gcc-plugin", the original name)
>> > * libclc
>> > * libcxx
>> > * libcxxabi
>> > * libunwind
>> > * lld
>> > * lldb
>> > * llgo
>> > * llvm
>> > * openmp
>> > * parallel-libs
>> > * polly
>> > * pstl
>> > * stacker (deleted after r40406)
>> > (Additionally, files added to the "monorepo-root/trunk" directory in
>> SVN end up at the root of this repository).
>> >
>> > Some SVN projects are still active, but not part of the LLVM codebase.
>> These get migrated to their own separate git repositories:
>> > * lnt
>> > * test-suite
>> > * www
>> > * www-pubs
>> > * www-releases ## TODO. Not done yet as it requires the use of
>> git-lfs, due to large files.
>> > * zorg
>> >
>> > A couple inactive projects which are somewhat related to the LLVM
>> codebase, migrated to separate repos:
>> > * poolalloc
>> > * safecode
>> >
>> > Legacy projects that are not particularly interesting, migrated to a
>> single separate git repository named "archive":
>> > * clang-tests # Copy of GCC 4.2 testsuite, modified to work with clang
>> > * clang-tests-external # Copy of GDB testsuite
>> > * llvm-gcc-4.0 # GCC 4.0, modified for llvm
>> > * llvm-gcc-4.2 # GCC 4.2, modified for llvm
>> > * llvm-gcc-4-2 # (merge with above)
>> > * java
>> > * vmkit
>> > * nightly-test-server
>> > * llbrowse # An LLVM bitcode GUI browser
>> > * television # A different LLVM GUI browser; shows effects of
>> transforms, etc
>> > * website # 2007-era snapshot of website, not actually maintained
>> here.
>> > * core, llvm-top, sample, support, hlvm # from the "HLVM" refactoring
>> attempt.
>> >
>> > Projects _not_ migrated from SVN in this conversion, since they're
>> elsewhere already:
>> > * giri # Never actually developed here; actually
>> https://github.com/liuml07/giri
>> > * klee # Already migrated to github with history;
>> https://github.com/klee/klee
>> >
>> >
>> >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >
>>
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