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From Daniel Shahaf <...@daniel.shahaf.name>
Subject Re: No-op changes no longer dumped by 'svnadmin dump' in 1.9
Date Wed, 23 Sep 2015 13:54:47 GMT
Daniel Shahaf wrote on Wed, Sep 23, 2015 at 13:07:31 +0000:
> Julian Foad wrote on Tue, Sep 22, 2015 at 12:54:58 +0200:
> > Daniel Shahaf wrote:
> > > Johan Corveleyn wrote:
> > >> [...], revision N-1 contains a real
> > >> change, but only a short log message; and revision N has a no-op
> > >> change to that same path, and a very informative log message [...]
> > >
> > > The FreeBSD project used to intentionally make no-op commits (they term it
> > > "forced commits") as part of their new committer workflow.  I don't know
> > > whether they still do that.
> > 
> > We need to be careful with terminology. We're not talking about a
> > no-op commit, we're talking about a path that is marked as 'changed'
> > within a commit, but whose content did not change. (The same commit
> > might or might not also contain other paths that have real changes.)
> > 
> 
> Yes, that is what I was referring to.
> 
> > In fact, I think one of the first things we need to do is a precise
> > analysis of the issue:
> > 
> >   * What exactly are the existing possible forms of 'no-op change'
> > that any part of Subversion can represent?
> >     - Text-change?
> 
> There's another hair to split here: a "no-op text change" can take two
> forms: either an _empty_ delta — that is, an svndiff stream with no
> windows — or a non-empty delta that, when applied to the source file,
> produces the source file again.
> 
> The former is conceptually
>     --- iota
>     +++ iota
>     [no hunks]
> 
> The latter is conceptually
>     --- iota
>     +++ iota
>     @@ -1 +1 @@
>     -This is the file 'iota'.
>     +This is the file 'iota'.
> 

Both of these are semantically equivalent, of course.  My point is that
we can't _detect_ no-op changes by looking for "an svndiff stream with
no windows", since such a test wouldn't catch all no-op changes: it
would be 100% specific but not 100% sensitive.

Cheers,

Daniel

> (saying "conceptually" because text deltas are _not_ unidiffs)
> 
> Cheers,
> 
> Daniel
> 
> >     - Props-change?
> >     - Whole-node-change?
> >     - Commit? (not so interesting in the current issue)
> >     - Only certain combinations of those?
> > 
> >   * At which APIs can each those changes be (a) made and (b) seen?
> >     - FS API?
> >     - Repos API?
> >     - RA and client-side APIs?
> >     - svnadmin dump/load?
> >     - svnrdump dump/load?
> >     - svnsync?
> > 
> > - Julian

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