[xwiki-dev] Groovy, Velocity, and XWiki syntax processing issues

[Erwan Arzur]

Hey Stephen

we recently had a discussion with Ludovic about choosing a rendering engine
and not mix both velocity and groovy.

About your UI proposal, i think it needs some more thinking because we might
want to plug other engines in addition to groovy and velocity, but i find it
better and easier to implement than my own idea which was to implement a
kind of preprocessor which would allow the user to select the rendering
engine to use for her document.

agree with your proposal about {pre} and {code} radeox tags, with the
provision that it might prove very complex to hide selected content from the
velocity/groovy engines.

Agree about error messages, they need a lot of improvements

And you're right about all those not fitting into a single JIRA issue :D

1. choosing a rendering engine. I'd like to add that mixing the two in a
document is a very bad design decision (but facts could prove me wrong),
just for the possible namespace collisions that could happen (your $varname
example)
2. {pre} syntax not coherent with other tag's
3. {pre} {code} specs should be amended
4. forcing enclose scripts into radeox tags

All this make significant syntax changes to make me wonder about existing
documents ... how to migrate them or make sure the old syntax is still ok
for them ?

Erwan

On 10/28/05, Stephen Schaub <stephen_schaub_88 at hotmail.com> wrote:
>
> When XWiki renders a document, the interactions between the Groovy,
> Velocity, and Wiki (Radeox?) syntax processing can lead to unexpected and
> undesirable behavior. There have been posts on this list in the past where
> this issue has been discussed. However, I'm not aware that any consensus
> has
> emerged as to how to deal with these problems.
>
> To summarize, here are a few of the issues that I'm aware of:
>
> * Getting XWiki to render a bit of text without doing any syntax
> processing
> on it can be difficult. For example, the {pre} ... {/pre} markup turns off
> XWiki syntax processing, but not Groovy processing.
>
> * The # symbol is used both to do numbered lists and is also used for
> Groovy
> processing. If a user wants to create a numbered list and forgets to put a
> space after the #, he can run into trouble. The following example will
> cause
> a stack dump:
>
> #bring coffee
> #include doughnuts
>
> * Code samples on a Wiki page sometimes don't render correctly, due to
> conflicts with Velocity syntax processing. The following C/C++ code sample
> results in a runtime stack dump:
>
> {code}
> #include <stdio.h>
> ...
> {code}
>
> * Groovy and Velocity both use $varname syntax. I think I've read some
> posts
> in the past where this was an issue -- although I can't come up with any
> examples at the moment.
>
> * A usability issue: Most XWiki tags ({table}, {code}, etc.) come in
> pairs.
> The closing tag has no slash. For example: {table} ... {table}. However,
> the {pre} tag does have a closing slash: {pre} ... {/pre}. This
> inconsistency is annoying and causes difficulties for new users.
>
> * A significant usability issue for Windows users: Pathnames contain
> backslashes (\). XWiki uses the backslash as an escape character. So
> attempting to put a UNC path like \\myserver\myshare\mydoc.txt in an XWiki
> document triggers an XWiki runtime exception. Boy, is that frustrating for
> new XWiki users. The solution is to wrap the path in {pre} .. {/pre}, but
> the error message gives the user no clue what the problem was, much less
> how
> to correct it.
>
> Here are some proposals for discussion:
>
> 1. {pre} ... {/pre} should turn off ALL syntax processing of its contents.
> 2. {code} ... {code} should turn off ALL syntax processing, except for
> syntax coloring.
> 3. {pre} should allow {pre} as a closing tag.
> 4. Consider requiring users to explicitly enable Groovy/Velocity
> processing
> for selected Wiki documents as needed. In the page editor, provide two
> checkboxes: "Perform Groovy Processing" and "Perform Velocity Processing".
> The user could separately enable either Groovy or Velocity processing, or
> both. People who enable them would presumably be in a better position to
> deal with the kinds of syntax conflicts that would occur.
> 5. Provide more user-friendly error messages when a Groovy or Velocity
> processing exception occurs. Show the Wiki source line that caused the
> problem.
>
> I haven't opened a JIRA issue for this yet, because I'm not sure how best
> to
> word it. But I think this is a high-priority issue that should be
> carefully
> addressed before the 1.0 release. This may be an issue that warrants a
> page
> on the xwiki.org <http://xwiki.org> developer site. I'll be glad to start
> one if the developers
> desire it -- perhaps here:
> http://www.xwiki.org/xwiki/bin/view/Dev/Discussions
>
> Stephen
>
>
>
>
>
>
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