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Re: [RFC] 'External' and 'Switched': common ground

From: Paul Burba <ptburba_at_gmail.com>
Date: Fri, 20 Aug 2010 11:34:48 -0700

On Fri, Aug 20, 2010 at 10:54 AM, Julian Foad <julian.foad_at_wandisco.com> wrote:
> What's the idea?
>
>
> External means Switched
> =======================
>
> Well, not quite! But at the WC layer they have a lot in common. Let's
> take advantage of it.
>
> In both cases:
>
> * An 'external' or 'switched' WC node is a file or a directory (tree).
>
> * An 'external' or 'switched' WC node is an immediate child of a
> versioned WC directory. [3]
>
> * An 'external' or 'switched' WC node is attached to a repository
> location other than the one implied by its WC parent directory.
>
> * In and inside itself, an 'external' or 'switched' file or tree is
> indistinguishable from any other WC file or tree. [4]
>
> * Only its relationship to its WC parent directory is 'special'. The
> only operations that may see it as different are those that start at
> a higher level (outside the node) and recurse or look into it, and
> those that start inside the node and walk up the tree towards the WC
> root.
>
> * Client operations treat the node as part of its parent WC in some
> ways, and treat it as special in other ways, depending on the
> command and on user-specified options.
>
>
> By defining 'External' and 'Switched' in terms of their common ground
> and their differences, we can reduce complexity and clarify the issues
> that are currently obscure. This could be especially helpful at the
> moment for designing their WC representation.
>
> How should we represent external files and external dirs in the WC in a
> unified manner? Do we need to explicitly mark them as 'external'? What
> differences in behaviour should 'external' nodes and 'switched' nodes
> exhibit within the WC?
>
>
> Differences in WC State
> =======================
>
> This table documents the differences in WC state at a high level.
>
> +----------------------+----------------------+----------------------+
> | | switched | external |
> +----------------------+----------------------+----------------------+
> | | | |
> | WC path affected | Existing child | Non-existent child |
> | | | |
> | Target URL | Same repo | Same or other repo |
> | | | |
> | Pinned to a revision | No [2] | Optional; recorded |
> | | | in 'svn:externals' |
> | | | |
> | Initial depth | Set by "switch" cmd | Infinity |
> | | | |
> +----------------------+----------------------+----------------------+
>
> ### Anything else?
>
>
> Differences in Client Commands (Current behaviour)
> ==================================================
>
> The following differences occur when a command encounters an 'external'
> or 'switched' node during its operation. This table is to document the
> current (1.6.x) behaviour.
>
> ### We'll need some test scripts to help gather this data.
>
> +----------------------+----------------------+----------------------+
> | | switched | external |
> +----------------------+----------------------+----------------------+
> | | | |
> | recursive descent, | yes | optional |
> | in general | | |
> | | | |
> | status | report & descend | report [& descend] |
> | | | |
> | propget/list/etc. | ? | ? |
> | | | |
> | diff | ? | ? |
> | | | |
> | commit | descend | [descend?] |
> | | | |
> | update | ? | ? |
> | | | |
> | switch | Can switch a WC root | No UI exists for an |
> | | but it's not then | external outside |
> | | recorded as such. | of a WC. |
> | | | |
> | ... | | |
> | | | |
> +----------------------+----------------------+----------------------+

Hi Julian,

FWIW, merge, when merge tracking is active, should* handle switched
vs. external subtrees quite differently.

Switched subtree affected by the merge: We need to record mergeinfo
such that the "missing" subtree doesn't appear to have had the change
merged to it (e.g. through subtree mergeinfo and non-inheritable
mergeinfo).

Switched subtree untouched by the merge: We can leave it alone (in 1.7
anyhow, because we no longer blindly update subtree mergeinfo).

External: Just ignore these from a merge tracking perspective. Note
that it is possible to contrive a situation where an external from the
same repository is affected by a merge, but it is such a contrivance
that I think we can safely ignore it.

* I say "should" because everything in not quite right yet, see
http://svn.haxx.se/dev/archive-2010-08/0088.shtml

Paul

> We ought to think about the UI and design a set of useful and consistent
> behaviours. But that's out of scope here; this document focuses on the
> WC layer.
>
>
> What to Do About It?
> ====================
>
> The first practical step I can see is to write a test suite utility for
> creating a WC with all the possible states in it, and first writing
> tests that just expose the current behaviour variations, and then
> deciding which of those are intended and which are bugs or awaited
> features.
>
> Any other suggestions on how to make some practical use of this idea?
>
>
> Footnotes
> =========
>
> [2] The ability for "svn update -rX" to "pin" that part of the WC at
> rX has been requested by users and seems like a reasonable (clean,
> moderately useful) feature.
>
> [3] You can "svn switch" a WC root, and the whole WC is then based on
> the new location, but it is not normally regarded as being in a
> "switched" state. The concept of a node being in a "switched"
> state is only meaningful with respect to the expected location as
> determined from the node's parent directory in the same WC. (The
> "svnversion" command has an option to specify an expected location
> so that it can report the status of the whole WC as "switched"
> relative to that specified location.)
>
> [4] A possible exception is that "update" should obey the "pinned
> revision number" if present. But that need not necessarily be an
> exception: we might choose to define that functionality on all WC
> nodes but only use it on 'external' nodes.
>
>
> - Julian
>
>
>
Received on 2010-08-20 20:35:27 CEST

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