Re: [Monotone-devel] long RFC: "contexts"

[graydon hoare]

Jon Bright wrote:

> manifest: <manifest-sha1>
> edge: <first-parent-context-sha1> {
>   renames: [<oldfilename>, <filename>] ...
>   adds: [<filename>, <file-sha1>] ...
>   dels: <filename> ...
>   changes: [<filename> <file-sha1>] ...
> }
> edge: <second-parent-context-sha1> {
>   renames: [<oldfilename>, <filename>] ...
>   adds: [<filename>, <file-sha1>] ...
>   dels: <filename> ...
>   changes: [<filename> <file-sha1>] ...
> }
>
> We've:
>
>  - renamed parent to edge
>  - renamed patches to changes (though we're not sure about that name 
> either)
>  - clarified that the filename in "changes" is the filename *after* any 
> renames have taken place

that all sounds good, and I can accept the logic of keeping 
author/date/comment/log as certs (possibly bundled), though I'm not 
*certain* it's better or worse. however:

>  - Removed the first <file-sha1> from the "changes" description.  With 
> the clarification about which filename the changes are acting upon, the 
> previous SHA1 isn't necessary - you know what SHA1 the parent's file of 
> that name had, so you know what you've gone from, you just need to 
> represent where you went to.

this change (and removing the edge parent's manifest sha1) I think I 
object to. the reason for preserving the pre-state content identifiers 
is that you can synthesize the manifest and file deltas without 
reconstructing and analyzing the pre-state manifest. that's an 
efficiency argument, but imo an important one (especially during 
networking), and I don't think it introduces any variable noise. i.e. I 
think the "extra" explicit information of file and manifest pre-states 
is identical to the synthetic information one would get by analyzing 
predecessor changes and manifests, in all cases, so the object is not 
any more semantically "minimal" without it, just takes fewer bytes. I'd 
argue for the presence of those extra bytes.

otherwise I think we're converging on a proposal. shall we discuss 
concrete syntax next? there are a dozen conflicting pressures there :)

-graydon