[llvm-dev] [monorepo] Exception in migrate-downstream-fork during monorepo transition

[Nagurne, James via llvm-dev]

Our team decided to try out the conversion process utilizing the tool from https://llvm.org/docs/Proposals/GitHubMove.html#basic-migration

However, we're currently blocked by an issue that I'd hope at least one other group who had used this script would have run into. I'm wondering if we've missed something fundamental, or if there's a new, more robust process in place and the documentation is out of date.

When running the script, I get the exception:

...
  File "../llvm-git-migration/migrate-downstream-fork.py", line 151, in commit_filter
    candidate_upstreams = [self.svn_to_newrev[p[0]] for p in parent_svn_info]
KeyError: 181274

svn_to_newrev is the mapping which help bridge the gap between old and new repos using the common svn revision.

In the monorepo, there's commit 2f2aeb9b. It seems to be an amalgamation of 3 svn revisions.
The log for this commit contains:

llvm-svn: 181277
llvm-svn: 181274
llvm-svn: 181273

However, when dumping out the svn_to_newrev map, I only get one reference to this commit:

181273: '2f2aeb9b6912046e9ea21ae259932c103333c444',

181274 is not present at all. This is a problem for commits whose parents include clang mirror commit f9abf237
https://github.com/llvm-mirror/clang/commit/f9abf23757fd6d417e20f1862dcf9a2794c76f16

The apparent assumption is that 1 monorepo commit is 1 svn revision, but this commit seems to break that assumption.
Any information or help is greatly appreciated! I loathe to attempt applying all of our changes manually, and would be happy to patch the script if there is in fact an error :)

I haven't tested it, but I'd bet the way to reproduce this would be:


1)      Checkout the llvm-mirror for clang

2)      Make a branch off of f9abf2375 and make a commit or two

3)      Attempt to use the migration script to move that branch onto the monorepo

Because that seems to be precisely what we did to cause the error.

Regards,
J.B. Nagurne
Code Generation
Texas Instruments
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