Re: Restoring detached HEADs after Git operations

From: Stefan Beller <sbeller@google.com>
Date: Jun 19, 2017, 19:21 UTC
Message-ID: <CAGZ79kYB__LOK5MhK_OrXYL1xYgYW0Hk5XfjYfRWAcH_AJ78uQ@mail.gmail.com>
In-Reply-To: <0092CDD27C5F9D418B0F3E9B5D05BE0801028B70@SBS2011.opfingen.plc2.de>

On Mon, Jun 19, 2017 at 11:09 AM, Patrick Lehmann <Patrick.Lehmann@plc2.de> wrote:

Show 5 quoted lines

> Hello Stefan,
>
> the use case is as follows:
>
> The projects consists of circa 18 IP cores. Each IP core is represented by a Git repository. Think of an IP core as of a lonestanding DLL or SO file project. Each IP core references 2 submodules, which bring the verification environments for testing the IP core standalone.

So phrased differently: You are using submodules to avoid "DLL hell" (sharing a lib, with ease of versioning as the submodules in the different IP cores may be pointing at different versions).

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>
> These 18 IP cores are grouped to bigger IP cores, referencing the low-level IP cores and each again the 2 verification submodules. Finally, the main project references the bigger IP cores and again the 2 verification cores.
>
> TOPLEVEL
>   o- IP1
>        o- UVVM
>        o- VUnit
>   o- IP2
>        o- UVVM
>        o- VUnit
>   o- IP3
>        o- UVVM
>        o- VUnit
>   o- IP4
>        o- UVVM
>        o- VUnit
>        o- IP5
>            o- UVVM
>            o- VUnit
>        o- IP6
>            o- UVVM
>            o- VUnit
>        o- IP7
>            o- UVVM
>            o- VUnit
>   o- IP8
>        o- UVVM
>        o- VUnit
>        o- IP9
>            o- UVVM
>            o- VUnit
>        o- IP10
>            o- UVVM
>            o- VUnit
>   o- IP11
>        o- UVVM
>        o- VUnit
>        o- IP9
>            o- UVVM
>            o- VUnit
>        o- IP12
>            o- UVVM
>            o- VUnit
>    o- UVVM
>    o- VUnit
>
> That's the simplified structure. I can't write more, because it's a closed source project. You can find other usecases e.g. in my other open source projects. E.g. The PoC-Library or The PicoBlaze-Library and the corresponding PoC-Examples repository.
>
> Example: PoC
> Pile of Cores includes 4 Git submodules and is itself an IP core library.
> So PoC-Examples again references PoC. This looks like this tree:
>
> PoC-Examples
>   |- lib/
>        o- PoC
>             |- lib
>                 o- Cocotb
>                 o- OSVVM
>                 o- VUnit
>                      o- .... OSVVM
>                 o- UVVM
>
> The library VUnit itself already includes OSVVM as a library.
>
> ----------------------
> Forcast:
> I'll write a new question / idea about multiple equal submodules and the memory footprint soon...
> Here is my original question posted on StackOverflow: https://stackoverflow.com/questions/44585425/how-to-reduce-the-memory-footprint-for-multiple-submodules-of-the-same-source
> ----------------------
>
> Do you need more use cases?
>

Well this use case points out a different issue than I hoped for. ;) From the stackoverflow post and from looking at the layout here, one of the major questions is how to deduplicate the submodule object store for example.

By use case I rather meant a sales pitch for your initial email:

    I use this bash script because it fits in my workflow because
    I need branches instead of detached HEADS, because $REASONS

and I'd be interested in these $REASONS, which I assumed to be
* easier to work with branches than detached HEADS (it aids the workflow)
* we're not challenging the underlying mental model of tracking sha1s in
  the superproject rather than branches.

At least I gave these reasons in the "reattach HEAD" stuff that I wrote, but maybe there are others? (I know the code base of submodules very well, but I do not work with submodules on a day-to-day basis myself...)