Re: partial evaluation / removing directives

Another option may be rewriting the AST tree after the template is parsed
and replacing some nodes with text or something else.
I tried that on the side as an experiment to inject some security checks
and collect profiling info for macros and templates.

Alex



On Fri, Jul 13, 2012 at 9:50 AM, Nathan Bubna <[email protected]> wrote:

> On Thu, Jul 12, 2012 at 2:27 PM, Pete <[email protected]> wrote:
> > Hi all,
> > I'm working with some velocity files where I want to partially evaluate
> > them, such that the only things actually evaluated are #parse (includes
> of
> > other velocity templates in the same directory) and  $references to a
> > resourceBundle variable passed in the context map.  In essence, all this
> is
> > doing is combining a number of velocity files into one master velocity
> > file, and localizing any resource bundle references to a given locale.
> All
> > the main velocity directives in the velocity file(s) should be left
> > unevaluated-   #set, #ifelse, #foreach etc. This way, the result could be
> > redistributed and modified specific to a particular locale, with just one
> > file instead of n based on the #parse structure.
>
> interesting challenge!  glad i don't have to do it though. :)
>
> > Up till now, I've been doing this in a somewhat roundabout way:
> > 1. setting strict escape property to true
> > 2. pre-processing the velocity templates by regexp replacing all
> instances
> > of #if / #else/ #elseif/ #end / #foreach / #define / #break / #stop
>  #set /
> > #evaluate with  \\#{$1}
> > This adds a an escape character before each of these directives, and I
> can
> > then call mergeTemplate on the result.  It works OK, sometimes, but I
> still
> > run into some parsing issues now and again (eg not a robust solution). It
> > also seems kind of heavy handed to have to preprocess these files using a
> > regular expression and saving them before velocity gets a handle on them.
> > It would even be a bit better if I could do this by reading them in and
> > doing the rgexp in-memory rather than on the saved files, then using
> > evaluate instead of mergeTemplate. But I assume that would cause problems
> > for the #parse directives.
>
> Why would evaluate cause problems for #parse??  If the engine is
> configured the same, the #parse should work the same whether you enter
> via file or string.
>
> > I know velocity added a removeDirective() method in 1.6.2 which seems
> like
> > it should be perfect for me - I could simply rip out all the directives
> but
> > #parse.  However, I tried the and it seems that it only works for certain
> > directives, eg  #foreach, #include, etc.  More basic directives like #if
> > and #elseif are not in the list of runtimedirectives, or even represented
> > as Directive objects, so removing them doesn't work.
>
> Yeah, they are deep in the parser.  Their structure doesn't work as a
> normal directive.
>
> > Any suggestions on the best way to proceed with this? Would it be easy to
> > change a few velocity files locally, recompile and get this behavior? Or
> is
> > it sufficiently complex removing all these more basic directives that I'm
> > better off continuing to try some kind of  preprocessing/ escaping?
>
> You would have to redesign Velocity's parsing deeply.  A major
> overhaul.  You're best off preprocessing.   Have you considered using
> a different template engine to do the first part (the parse and
> resourceBundle resolution)?  Might be overkill, but might be easier,
> so long as the syntax has no overlap with VTL.
>
> > thanks,
> > Pete
>
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