I don't like the command.com like scheme either. A scheme like that of
sh or a strict ${pattern} is far more extensible and far less likely to
collide with other use cases.
The windows scheme doesn't support anything more than ascii variable
names, while many implementations have different workarounds. And we
have more than enough escaping problems via white space paths and
quoting characters being valid in paths.
Bert From: Julian Foad
Sent: 11/06/2013 10:48
To: Daniel Shahaf
Cc: Gabriela Gibson; Gabriela Gibson; dev_at_subversion.apache.org
Subject: Re: Review of invoke-diff-cmd-feature branch
Daniel Shahaf wrote:
> Gabriela Gibson wrote on Mon, Jun 10, 2013 at 23:39:45 +0100:
>> On 6/10/13, Daniel Shahaf <danielsh_at_elego.de> wrote:
[...]
>> >> ---------- **** ------------
>> >>
>> >> + How does this parse "%%%f1%"? Is "%%f1%%" an error?
>> >>
>> >> %%%f1% becomes %%f1% and %%f1%% becomes %f1%%, neither is an error.
>> >>
>> >> However, %f1%% is parsed out as sub%, also, +%f1% ends up as +sub.
>> >
>> > I'm not sure I understand. I expect %%%f1% to become %sub and %f1%% to
>> > be either an error or sub%. Is that what is implemented?
>>
>> No. We sub only %f1% where we find it, but if it's escaped with
>> one or more %'s, we eat exactly one of those instead, so %%%f1% becomes
>> %%f1%.
>
> That's not the behaviour I would expect. What I would expect is what I
> mentioned in my question: that the string is parsed left-to-right, and
> whenever an % is seen, the next character is either % in which case a
> literal % is emitted, or 'f1%' (or one of the other five replaceables)
> in which case it is replaced; if it is anything else, the behaviour is
> undefined / not promised.
>
>> %f1%% becomes sub% as per request by Julian Foad, because some
>> diff clients accept syntax like +sub and sub+ (so, you'd use
>> +%f1% and %f1%+ respectively to get that).
>
> Okay. I would have expected '%f1%%%' were required to get 'sub%', and
> leave the case of a 'foobar%' (and '%f1%%') as undefined behaviour.
>
> What do others think about these %-escaping issues?
There are lots of variable-substitution (or 'interpolation') schemes
in the world already -- please don't invent another one. Choose an
existing scheme, look up the spec on the Internet and reference it,
and then implement (the relevant parts of) it.
If there's a scheme that we're already using in Subversion, that would
be a good choice. Is there one? If not, I don't much like the
Windows '%foo%' scheme because it's rather irregular compared to
others, but if that's what we want to use then I guess that's OK with
me, but again, find the spec on the Internet and refer to that.
- Julian
Received on 2013-06-11 11:10:33 CEST