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Re: multiple targets for 'svnlook propget'

From: Paul Burba <ptburba_at_gmail.com>
Date: Fri, 16 Nov 2012 13:04:31 -0500

On Fri, Nov 16, 2012 at 10:58 AM, Julian Foad
<julianfoad_at_btopenworld.com> wrote:
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> ----- Original Message -----
>> From: Johan Corveleyn <jcorvel_at_gmail.com>
>> To: Julian Foad <julianfoad_at_btopenworld.com>
>> Cc: Subversion Development <dev_at_subversion.apache.org>
>> Sent: Friday, 16 November 2012, 8:54
>> Subject: Re: multiple targets for 'svnlook propget'
>> On Fri, Nov 16, 2012 at 1:19 PM, Julian Foad <julianfoad_at_btopenworld.com>
>> wrote:
>>> Johan Corveleyn wrote:
>>>> Right now, 'svnlook propget' supports only a single
>>>> argument:
>>>> usage: 1. svnlook propget REPOS_PATH PROPNAME PATH_IN_REPOS
>>>> I think it would be useful to support multiple targets, like 'svn
>>>> propget'. That would make it much faster to gather all props set
>>>> during a transaction, for instance in a pre-commit hook:
>>>> svnlook propget -t $TXN $REPOS svn:eol-style `svnlook changed -t
>>>> $TXN $REPOS`
>>>> The only complication I see, is that the output for multiple targets
>>>> has to write the node for which the properties are shown.
>>>> Looking at 'svn propget' for inspiration, we see that it
>> doesn't
>>>> output the node when there is only one target. But it does when there
>>>> are multiple targets. I guess 'svnlook propget' could implement
>> the
>>>> same behavior, which means that the output for single target remains
>>>> backwards compatible (at the cost of slight increase of complexity for
>>>> scripts that parse that output -> they have to know if they passed
>> one
>>>> or mutiple targets).
>>>> Current output of 'svn propget':
>>>> $ svn pg svn:eol-style ^/file.txt
>>>> native
>>>> $ svn pg svn:eol-style ^/file.txt ^/binary.exe ^/file2.txt
>>>> http://my.svn.server/svn/file.txt - native
>>>> http://my.svn.server/svn/file2.txt - native
>>>> (As you can see, the it simply does not output the targets that
>> don't
>>>> have the property, and shows the actual target for every file that
>>>> does)
>>>> Or with working copy targets:
>>>> $ svn pg svn:eol-style file.txt binary.exe file2.txt
>>>> file.txt - native
>>>> file2.txt - native
>>>> Now, when we look at the output of 'svnlook propget':
>>>> $ svnlook pg repos svn:eol-style file.txt
>>>> native
>>>> We could have following multi-target output:
>>>> $ svnlook pg repos svn:eol-style file.txt binary.exe file2.txt
>>>> file.txt - native
>>>> file2.txt - native
>>>> Thoughts?
>>>> P.S.: This multi-target output isn't very parseable for multi-line
>>>> properties. Currently, 'svn propget' also has this problem, but
>> users
>>>> can use --xml to get machine-readable output.
>>> I added a "svn propget --verbose" mode (in 1.7 I think) to
>> resolve that problem. It uses the same format as "svn proplist
>> --verbose", which is like this:
>>> [[[
>>> $ svn pg -vR svn:ignore # selected bits of output are shown
>>> Properties on 'subversion/bindings/ctypes-python/csvn/ext':
>>> svn:ignore
>>> *.pyc
>>> Properties on 'subversion/mod_dav_svn/reports':
>>> svn:ignore
>>> .libs
>>> Properties on 'contrib/server-side/svnstsw/include':
>>> svn:ignore
>>> Makefile
>>> Makefile.in
>>> ]]]
>>> If the email system hasn't mangled the white space, you should be able
>> to see that the prop name is indented by two spaces and the value by four
>> spaces, and newlines in the value are preserved (with exactly one LF added to
>> ensure there is a line break in the output) so it's fully parseable.
>>>> Maybe 'svnlook propget'
>>>> should eventually also grow a --xml option to handle this. But I'd
>> say
>>>> that's yet another feature. For now, I would be happy if svnlook
>> could
>>>> already do "plain" output for multiple targets, which can
>> already be
>>>> useful/parseable for single-line properties like svn:eol-style.
>>> Given that 'svnlook' is very much expected to be used by scripts
>> ('svn' serves most human-interaction cases), I don't see
>> implementing the "plain" output is a good idea.
>>> But +1 on implementing the "svn pg -v" format.
>> Ok, but then you probably mean that I should add two things:
>> 1) Add multi-target support to 'svnlook pg'
>> 2) Add -v to 'svnlook pg', format like 'svn pg -v'
>> The combination of 1 and 2 would then give us a parseable output for
>> multiple targets.
>> But I guess I shouldn't forbid the use of 1 without 2, right? I think
>> it would be strange to say "cannot use multiple arguments without
>> --verbose" ...
>> So it seems I should also provide a format for the multi-arg case
>> without -v ... like the current format of 'svn pg' without -v.
>> I also note that the same enhancement can't easily be made for
>> proplist. Mainly because 'svnlook pl' already has a --verbose option,
>> so we can't change the output of 'svnlook pl --verbose' with a
>> single
>> target without breaking backwards compatibility.
>> - 'svn pl' always shows "Properties on 'XXX':"
>> (whether for single
>> target or multiple targets, whether verbose or not)
>> - 'svnlook pl' does not, and when used with --verbose it doesn't
>> indent multiline properties like 'svn pl' does.
>> [[[
>> $ svn pl sources --verbose
>> Properties on 'sources':
>> svn:ignore
>> .classpath
>> .settings
>> .project
>> $ svnlook pl repos trunk/sources --verbose
>> svn:ignore : .classpath
>> .settings
>> .project
>> ]]]
>> Currently I'm mainly focused on propget, so proplist doesn't bother me
>> too much. But it would of course be even better if proplist behavior
>> would match the propget behavior. If anyone has any ideas for this ...
> It seems to me that the 'svnlook pl --verbose' output is pretty useless. Well, OK, not useless, but poor. IIRC 'svn pl --verbose' was like that and I changed it to use the new format, at the same time as I changed 'svn pg --verbose' to use the new format. In terms of back-compat, however, 'svn pl --verbose' didn't exist before I added it, whereas I changed the output of 'svn pl --verbose' in an incompatible way. I simply decided that the latter was an acceptable change.
> Apart from backward compatibility concerns, I would totally go for making 'svn pg' and 'svn pl' and 'svnlook pg' and 'svnlook pl' all use the indented & parseable format, and not relate it to the '--verbose' option at all.


> I dunno, add a '--parseable' (or should that be '--parsable') option to select the new format?

I prefer the backward incompatible format change over a new option.
It's a slippery slope if, every time we want to change the format of a
command line program, we add a new option. What if we later change
the format of the optioned output?

Paul T. Burba
CollabNet, Inc. -- www.collab.net -- Enterprise Cloud Development
Skype: ptburba
> - Julian
Received on 2012-11-16 19:05:05 CET

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