The content of this blog is my personal opinion only. Although I am an employee - currently of Imagination Technologies's MIPS group, in the past of other companies such as Intellectual Ventures, Intel, AMD, Motorola, and Gould - I reveal this only so that the reader may account for any possible bias I may have towards my employer's products. The statements I make here in no way represent my employer's position, nor am I authorized to speak on behalf of my employer. In fact, this posting may not even represent my personal opinion, since occasionally I play devil's advocate.

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Thursday, August 14, 2014

Versioned Label Sets

I like labels in version control systems. Like "Compiles". "Passes Tests".  "Passes all tests except Test#44".   Status if you will.

Of course, such status must be applied to set of files+versions.  Or a repo-project-version. Whatever.  (I will not use the whole-repo-project viewpoint here, since I am trying to think about partial checkouts. Whole-repo trivially fits - it is just a single entry, the rep version.)

You can think of a label as a file itself, containing a list of files and their version numbers.   Such a label-file might also contain branch info, etc. - i.e. more metadata.

Generalize to an arbitrary package of metadata associated with a set of files+versions.  "Labels" may be such that their name is the only metadata that matters.

Such a label-or-metadata-file can itself be versioned.  Must be, should be.

In fact, just about everything we care about can be considered a set of objects+versions, in a file, itself versioned.  

Branches may be defined by rules such as a list of filenames or patterns.  Possibly with versions that are frozen in the branch. 

OK, there is a difference: branch histories are graphes.  Steps along the history are the sets of objects+versions that most closely correspond to a label set.  

I.e. there are graphs whose nodes are objects+histories.  

Anyway... : the default action is where the difference arises.

When a workspace is checked out from a branch head, when trying to check in the default is to extend the branch. 

When a workspace is checked out from a label, the default is not to extend. The label.

We can imagine interconversion: forcing a checkin to a label, making the label into a branch.


Who stores the linkages?

Label-sets may be marked inside a branch-graph file, or outside.

Outside allows non-privileged access.  Library users can label library versions.

Inside may be faster and more convenient.

It is important to be able to track the configuration of stuff that you are not allowed to write into the "home" VCS for. 

The DVCS people say "just clone", but that may not always be possible

I may want to have a local repo, linked to a master repo without incorporating all, and be able to define cross repo actions.

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