2.4: Defaults handling; string conversion inconsistencies; and laziness vs annotations

Folks,

I made quite a lot of changes last night in the 2.4 tree to support  
handling of defaults-relying-on-other-parameters in macro parameters  
lists. In 2.4, the situation is of course more tricky, as defaults can  
also be specified in Java annotations for directive, method, and  
transform models. This all now works. In the course of it, I did  
discover and fix few other bugs, namely:
- defaults in annotations weren't filled in at all when the directive/ 
transform was called with no arguments, i.e. if there was a

@Parameters("a=1 b=2")
public class FooDirective implements TemplateDirectiveModel {
    ...
}

and it was invoked as

<@foo/>

then defaults weren't filled in. If there was at least one argument:

<@foo a=2/>

then the defaults were filled in correctly. This had to do with an  
unfortunate use of null for no-args. I solved it by introducing a  
special "EmptyArgs" class extending ArgsList (arguably, I could've  
just used a zero-arg NamedArgsList, but this also allowed for using a  
faster call path).

Also, the model->string conversion needed for TemplateMethodModel that  
is not a TemplateMethodModelEx worked differently for non-annotated  
methods than for annotated methods. For non-annotated ones, it used  
Expression.getStringValue(model, expression, environment) (correctly,  
as it did in 2.3.x). For annotated ones, it used  
((TemplateScalarModel)model).getAsString(). I fixed that.

Finally, if a method class that implements LazilyEvaluatableArguments  
has a Parameters annotation, then its arguments will be eagerly  
evaluated. I'll say I can live with this limitation for the time  
being; I've just documented it it in the LazilyEvaluatableArguments  
JavaDoc; if you agree.

Attila.

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