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From Boris Partensky <boris.parten...@gmail.com>
Subject Re: upgrading from 1.5 to 1.7 compatibility issues
Date Mon, 30 Apr 2012 19:37:40 GMT
No problem, thanks for making things clear.

<< we decided to forego it and notify users of the non-BC change when
we released 1.7.

which notification are you referring to? Wonder if there is something
else in there I am not aware of.


On Mon, Apr 30, 2012 at 2:34 PM, Nathan Bubna <nbubna@gmail.com> wrote:
> Congratulations, Boris.  You are the corner case we feared.  :-/  We
> knew when we went ahead with this that providing a migration path
> would be difficult.  We knew most users didn't have extreme numbers of
> macros and hoped that those who didn't frequently nest them, in part
> because of the complexities of heavy scoping in a language that often
> treated scoping as a second-class feature, and in part because of the
> performance issues macros had prior to 1.6.  #parse,
> VelocityLayoutServlet and even custom tools, which lack the implicit
> scoping support, tended to be more performant and encouraged for
> simplifying complicated tools.  Considering those things and the
> difficulty of implementing a BC switch for implicit scoping, we
> decided to forego it and notify users of the non-BC change when we
> released 1.7.
>
> Sorry.  It sounds like it's going to take some legwork to upgrade in
> the cases where you nested your macros.
>
> On Mon, Apr 30, 2012 at 11:16 AM, Boris Partensky
> <boris.partensky@gmail.com> wrote:
>> Yep, I am afraid we do set globals from within macros...
>>
>> On Mon, Apr 30, 2012 at 2:05 PM, Nathan Bubna <nbubna@gmail.com> wrote:
>>> Can you set velocimacro.context.localscope = true or is it important
>>> for your system to be able to #set global stuff from within macros?
>>>
>>> On Mon, Apr 30, 2012 at 10:50 AM, Boris Partensky
>>> <boris.partensky@gmail.com> wrote:
>>>> Thanks Nathan, I think I do get the whole scoping idea, but my
>>>> understanding was that one of the reasons to turn all scoping off by
>>>> default (and have those properties to begin with) was to provide
>>>> backward compatibility - as in: I upgrade to 1.7 and then I start
>>>> turning on all those nice bells and whistles and use scopes and what
>>>> not. Not so seems like? I also find somewhat strange that a a formal
>>>> argument to a macro takes precedence and overwrites a global variable
>>>> with the same name. How would one go about upgrading existing systems?
>>>> We have roughly 1900 macros, big chunk of those are nested... Maybe I
>>>> am misunderstanding something, but this issue makes it almost
>>>> impossible to upgrade (at least for us).
>>>>
>>>>
>>>> Thanks
>>>> Boris
>>>>
>>>> On Mon, Apr 30, 2012 at 12:55 PM, Nathan Bubna <nbubna@gmail.com> wrote:
>>>>> Yeah, it was intended, and part of an overall move toward
>>>>> fixing/simplifying Velocity's variable scoping, avoiding the
>>>>> complexities and costs (performance, yes, but mostly time/brainpower
>>>>> for users and devs alike) of more programming language type behavior.
>>>>> Velocity has long aspired to be a straightfoward template engine and
>>>>> avoid being a complete scripting language.  (Implicit) variable
>>>>> scoping, as seen in 1.5, was seen as a necessary compromise toward the
>>>>> latter; after all, one big fat namespace is always unmanageable,
>>>>> right?  Well, there's ways to make that easy to manage. :)  Let's call
>>>>> it "optional, provided, explicit scoping", explicit because you don't
>>>>> have to grok the contextual scope to understand a reference, optional
>>>>> because you can ignore it, and provided because Velocity does the work
>>>>> of choosing "prefixes" and creating/destroying the scopes (as any
>>>>> implicit scoping system does).  So everything is becoming globally
>>>>> scoped, but it is now trivial to turn on automatic, explicit scopes or
>>>>> namespaces that you can use when you don't want things to live in the
>>>>> global scope.
>>>>>
>>>>> Here's an example...  Do you use $velocityCount to get an index of
>>>>> sorts inside of #foreach directives?  Well, that's an example of mixed
>>>>> implicit/explicit namespacing that gets messy when you nest
>>>>> #foreach's, with no good way to get the parent's count and
>>>>> unwieldiness when you want to add $velocityIndex, $velocityHasNext and
>>>>> so on.  Now, we automatically manage a $foreach var that not only has
>>>>> a 'count' property, but an 'index', 'hasNext', 'parent', and so on
>>>>> (see http://velocity.apache.org/engine/devel/apidocs/org/apache/velocity/runtime/directive/ForeachScope.html).
>>>>>  It also, of course, accepts any property you want to set on it (like
>>>>> any map).  This makes templates instantly understandable, making
>>>>> debugging much better.  You always know exactly what you are referring
>>>>> to, and so does anyone else reading the template.
>>>>>
>>>>> #foreach is the only 'content directive' that has its explicit scope
>>>>> automatically turned on, but all content containing directives
>>>>> (including custom body macros) can have their own explicit,
>>>>> auto-managed scope, named after themselves.  for example, you can flip
>>>>> the macro scope on:
>>>>>
>>>>> macro.provide.scope.control = true
>>>>>
>>>>> and do:
>>>>>
>>>>> #macro( outer $arg )
>>>>>  #set( $macro.arg = $arg )
>>>>>  #inner( 'inner' )
>>>>> #end
>>>>> #macro( inner $arg )
>>>>>  #set( $macro.arg = $arg)
>>>>>  inner: $macro.arg
>>>>>  #if( $macro.parent )outer: $macro.parent.arg#end
>>>>> #end
>>>>>
>>>>> #outer( 'outer' )
>>>>> #inner( 'just inner' )
>>>>>
>>>>> and get
>>>>>
>>>>>  inner: inner
>>>>>  outer: outer
>>>>>  inner: just inner
>>>>>
>>>>> Hope this helps...
>>>>>
>>>>> In any case, there was plenty of thought and discussion that went into
>>>>> this change.  Search http://velocity.markmail.org for 'scope' and you
>>>>> should find more on this.
>>>>>
>>>>> On Mon, Apr 30, 2012 at 8:49 AM, Boris Partensky
>>>>> <boris.partensky@gmail.com> wrote:
>>>>>> Hello, while going through the upgrade I noticed an incompatible
>>>>>> behavior during nested macro evaluation. Looks like in 1.7 (all
>>>>>> default properties) child macro has access to variables set in parent
>>>>>> macro scope (and those take precedence over globals), and 1.5 sees
>>>>>> globals. In the following example, in 1.5 unit test the following
>>>>>> template will evaluate to "globalvar", and in 1.7 - to
>>>>>> "outermacroparam". Is this expected behavior?
>>>>>>
>>>>>>
>>>>>> 1.5 test case
>>>>>>
>>>>>>
>>>>>> public void testVelocityNestedMacroScope() throws Exception
>>>>>>    {
>>>>>>        VelocityEngine ve = new VelocityEngine();
>>>>>>
>>>>>>        ve.init();
>>>>>>
>>>>>>        String template = "#macro(outerMacro $arg1)"+
>>>>>>                          "#innerMacro('blah')"+
>>>>>>                          "#end"+
>>>>>>                          "#macro(innerMacro $arg2)$arg1#end"+
>>>>>>
>>>>>> "#set($arg1='globalval')#outerMacro('outermacroparam')";
>>>>>>        StringWriter eval = new StringWriter();
>>>>>>        boolean b = ve.evaluate(new VelocityContext(), eval, "foo",
template);
>>>>>>        assertEquals(eval.toString(), "globalval", eval.toString());
>>>>>>
>>>>>>    }
>>>>>>
>>>>>> 1.7 test case
>>>>>>
>>>>>>
>>>>>>  public void testVelocityNestedMacroScope()
>>>>>>    {
>>>>>>        String template = "#macro(outerMacro $arg1)"+
>>>>>>                          "#innerMacro('blah')"+
>>>>>>                          "#end"+
>>>>>>                          "#macro(innerMacro $arg2)$arg1#end"+
>>>>>>
>>>>>> "#set($arg1='globalvar')#outerMacro('outermacroparam')";
>>>>>>        String eval = evaluate(template);
>>>>>>        assertEquals(eval, "outermacroparam", eval);
>>>>>>
>>>>>>    }
>>>>>>
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