[llvm-dev] [monorepo] Much improved downstream zipping tool available

[Björn Pettersson A via llvm-dev]

> -----Original Message-----
> From: David Greene <dag at cray.com>
> Sent: den 30 januari 2019 22:44
> To: Björn Pettersson A <bjorn.a.pettersson at ericsson.com>
> Cc: llvm-dev at lists.llvm.org; cfe-dev at lists.llvm.org; openmp-
> dev at lists.llvm.org; clangd-dev at lists.llvm.org; libclc-
> dev at lists.llvm.org; libcxx-dev at lists.llvm.org; lldb-dev at lists.llvm.org
> Subject: Re: [monorepo] Much improved downstream zipping tool available
> 
> Björn Pettersson A <bjorn.a.pettersson at ericsson.com> writes:
> 
> > In llvm (split) we have:
> >
> >   UL4->UL3->UL2->UL1->UL0
> >                    \
> >          ...->DL2->DL1
> >
> > In clang (split) we have:
> >
> >   UC4->UC3->UC2->UC1->UC0
> >                    \
> >          ...->DC2->DC1
> >
> >
> > DL1 is a commit that updates the clang submodule to DC1 (and in this
> > scenario at the same time merges UL1 and DL2 in llvm).
> 
> Ok, in that case I would expect the resulting history to look like
> this:
> 
>     UL4->UC2->UL3->UL2->UL1->UL0->UC1 <- monorepo/master
>                          |         \
>                          \          `---.
>                           `------------. \
>                                         \|
>                             ... ->DL2->DL1/DC2 <- zip/master
>                                         /
>                             ... ->DC2--'
> 
> As a submodule update, DC1 is "inlined" into DL1 and its commit message
> is appended to that of DL1.  I'm presuming here that llvm never updated
> the clang submodule to DC2, so it remains an independent commit.
> 
> The inlining is done assuming that submodule updates represent a single
> logical change.  Submodule updates are assumed to be related to
> whatever
> changes happen in the umbrella so they all get smushed together into
> one
> commit.
> 
> The edge UC1->DL1 represents the use of UC1 tree for every project
> *except* llvm, because clang was a submodule of llvm (and updated to
> DC1
> which merged UC1) and no other project was a submodule in llvm.  DL1
> still has the llvm tree from UL1 plus any local changes you may have
> made.

I still do not understand how that actually works technically, but maybe
it does if you say so. But I also believe that "git log" etc on DL1/DC2
will show that commit UL0 is part of my tree (which it isn't?). This will
be really confusing when looking back at the history when debugging etc.