[llvm-dev] New LLVM git repository conversion prototype

Tue Oct 16 15:16:34 PDT 2018

On Mon, Oct 15, 2018 at 7:58 AM Danila Malyutin <
danila.malyutin at synopsys.com> wrote:

> Great to hear!
>
> Are there some migrations strategies for those who are using llvm-mirror
> repositories?
>
>
It'd be great if someone wrote down some exact step-by-step instructions
for this. :)

But, basically -- if you're migrating from another monorepo repository with
the same layout, but different hashes, I find the easiest procedure is to
simply add the new upstream into your existing repository and then rebase
your branches onto the new upstream.

An alternative scheme, which has the advantage of also working if you're
converting from separate repositories to a monorepo, is to run something
like "git format-patch --stdout origin/master..mybranch > mybranch.patch",
for each of your branches you want to save, and then, in a new repo, create
new branches, and use "git am" to apply your patch. If you're converting
from non-monorepo, then you can use the "--directory" argument to "git am"
to apply the patch onto a subdirectory of the repository.

> I’ve noticed that some projects in llvm git prototype not only have
> different commit SHAs (which is expected, since the commit messages are
> slightly different due to llvm-svn=N), but also different histories (first
> lnt commit in llvm-mirror is 2 years older than in prototype).
>
>
I hadn't noticed that difference in the lnt history before -- looking into
it now, I see that this is due to the initial checkin of /lnt/trunk being
an svn copy of /zorg/trunk/lnt.

Because git-svn effectively runs "svn log llvm-project/lnt/trunk" to
populate its copy, and that follows the history of trunk across the initial
copy-from, that migration gets the history from before the copy. The new
conversion uses path-based filtering of the entire tree, rather than
following one path's log.

LNT is the only project which has this particular property. My inclination
is to leave this as is -- to leave the previous history in the zorg
repository. But it would also be possible to remove zorg/trunk/lnt from the
zorg repository history, and instead put it into the LNT git history.

*From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *James
> Y Knight via llvm-dev
>
*Sent:* Friday, October 12, 2018 01:28
> *To:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* [llvm-dev] New LLVM git repository conversion prototype
>
>
>
> TLDR: https://github.com/llvm-git-prototype/
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_llvm-2Dgit-2Dprototype_&d=DwMFaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=YgdxWMcdqQPlU9EdetI-xI79G7ouw9_Us0dFsZnFQYU&m=N77kJ4LaWGbhMLDMsmsaWXefS9f6W0IZTDHibv5dCkc&s=K66CatS6_rX7Z84fG40bYi-BFdj1EH-Ge7BuasqHwaQ&e=> 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
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_docs_Proposals_GitHubMove.html&d=DwMFaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=YgdxWMcdqQPlU9EdetI-xI79G7ouw9_Us0dFsZnFQYU&m=N77kJ4LaWGbhMLDMsmsaWXefS9f6W0IZTDHibv5dCkc&s=qS4wDBMYZgiJajPClPRreKzuXJVsb2635t3auD50xhk&e=>,
> 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
> <https://urldefense.proofpoint.com/v2/url?u=http-3A__travis-2Dci.org&d=DwMFaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=YgdxWMcdqQPlU9EdetI-xI79G7ouw9_Us0dFsZnFQYU&m=N77kJ4LaWGbhMLDMsmsaWXefS9f6W0IZTDHibv5dCkc&s=DeqmBM4n_BBYesAelEv-fMXEE5koKo0ZQVco3Pt2kOI&e=>)
> 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
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_liuml07_giri&d=DwMFaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=YgdxWMcdqQPlU9EdetI-xI79G7ouw9_Us0dFsZnFQYU&m=N77kJ4LaWGbhMLDMsmsaWXefS9f6W0IZTDHibv5dCkc&s=_CpoeuN6AI232B9eqd28X5dAI8MoTC6_t5vDWz8f_2c&e=>
>
>   * klee # Already migrated to github with history;
> https://github.com/klee/klee
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_klee_klee&d=DwMFaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=YgdxWMcdqQPlU9EdetI-xI79G7ouw9_Us0dFsZnFQYU&m=N77kJ4LaWGbhMLDMsmsaWXefS9f6W0IZTDHibv5dCkc&s=UTwnvwghVXONKHDJjon3lvCG3ZRJT-xZDJmAb3whxIw&e=>
>
>
>
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