Thomas Mortagne created VELOCITY-967:
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Summary: Allows passing a list of Template instances to
Template#merge
Key: VELOCITY-967
URL: https://issues.apache.org/jira/browse/VELOCITY-967
Project: Velocity
Issue Type: Improvement
Components: Engine
Affects Versions: 2.3
Reporter: Thomas Mortagne
Instead of the list of template names.
In [XWiki|https://www.xwiki.org] it's possible to define Velocity macros in all
kind of locations (files, pages, attachment in a page, object fields, etc.),
they can include each other but more importantly you can have several Velocity
scripts in the same page (or a page which included several other pages and now
has several scripts) with one of the scripts reusing macros defined in a
previous one.
So far, it was not too much of a problem, I just kept reusing the same Template
instance:
{{code}}
currentTemplate.setResourceLoader(new SingletonResourceReader(script));
currentTemplate.process();
currentTemplate.merge(context, out);
{{code}}
repeat...
But I'm starting to work on caching compiled Velocity (i.e. {{Template}}
instances) and execute them later in various different contexts. It's not a
problem for variables since they are stored in the context, but there is still
a problem for which I don't have a clean solution: passing current macros
(gathered from previous executed templates) to the currently executed one. I
first thought I could just call VelocityContext#setMacroLibraries before
template.merge(mergeContext, out); but unfortunately, merge "breaks" the
current context (it replaces the context macro libraries by an empty list) and
using template.merge(mergeContext, out, names); and a custom ResourceManager
would add too much complexity for various use cases.
My current workaround is to pass a custom Velocity context which overwrite
setMacroLibraries and ignore any call with an empty list as parameters (yeah,
not a huge fan either).
The simplest for us would be to pass directly the macro libraries Template
instances of Template#merge (to be perfectly honest, passing just the macros is
our real need but passing a Template list is more generic and in line with what
Template#merge is already doing in practice).
My plan is to write a (very easy) pull request, but I wanted to discuss the
idea first to see how well it's received.
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