[llvm-dev] New LLVM git repository conversion prototype

Tue Oct 23 11:44:12 PDT 2018

On Tue, Oct 23, 2018 at 10:07 AM NAKAMURA Takumi <geek4civic at gmail.com>
wrote:

> James,
>
> I have checked through your repo.
> I don't find any major issues, at least on trunk, for guys to play on.
>
> A couple of minor concerns.
> Note, I gave up inspecting commits older than r37632.
> I just grafted from it.
> I haven't checked branches yet. I think branches may be rewound easily.
>
>
> 1) Consistency of empty commits
>
> I didn't conclude how they are handled. Almost all of them are
> svn-specific,
> for example, to change props or to remove dirs.
> I wonder they are partial.
>
> FYI, I found almost all commits that touched particular subrepo.
> For example, r1, creating repos. I miss it!
>

It looks like what's happening is that svn2git is excluding commits
containing only directory additions and changes of directory properties.
E.g. r313601 was excluded. It doesn't exclude a commit consisting only of
deletions of empty directories, however, so e.g. r342803 was kept.

My preference is "all or nothing" :)
>

Yes, I think it's probably best to preserve the empty directory add+modify
commits. I'll fix this...

> I guess this issue would depend on svn2git.
> I gave up using svn2git.
>
>
> 2) Glitches of authors who have changed their name
>
> I found too many commits that have incompatible author filed.
> I heard from you, you have sought through commits, mailing lists.
> But I don't think all of glitches would be intentional.
>

Indeed -- oops! I managed to insert an off-by-one error into the author
mapping function, so there's a mismatch at every revision where the mapping
changes. Fixing that...

> Could you recheck? I have checked that my master repo can recreate
>
just identical commits against individual llvm.org/git.
>
> I could gather such glitches, or send you my authors.txt.
>
>
> I think the migration may be done more carefully, at least span of weeks.
> I wonder why guys are too urgent.
>

I'm going to keep iterating, as long as these sorts of issues are being
actively looked for and discovered. People are also anxious to get started
with the next steps, which depend on a finalized repo, so I'm just hoping
that doesn't go on for too long, but I'm happy as long as we're making
active progress towards that goal!

Thanks for all your great help in checking things out so far!!

ps. I realized git-fast-export was really useful for this case. :p
>

>
> Takumi
>
>
> On Fri, Oct 12, 2018 at 7:28 AM James Y Knight via llvm-dev <
> llvm-dev at lists.llvm.org> 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.
>>
>> 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)
>> 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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