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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 20:06:01 GMT
I am seeing 3 bullet points there pertinent to this issue and all 3
seem to indicate that being compatible was the intention there, or am
I wrong ? The way I read #2 and #3 is that the parent scope should
only be available if I explicitly specify the scope I want (parent or
topmost or replaced).

* For performance and compatibility these are all off by default,
*except* for $foreach. The others may be enabled by setting a velocity
property like:macro.provide.scope.control = true
* When scopes of the same type are nested make the parent Scope
available through the child (e.g. $foreach.parent or
$foreach.topmost).
* When a Scope reference overrides an existing reference that is not a
Scope, make it available through the Scope (e.g. $foreach.replaced).

On Mon, Apr 30, 2012 at 3:51 PM, Nathan Bubna <nbubna@gmail.com> wrote:
> http://velocity.apache.org/engine/devel/changes-report.html#a1.7
>
> On Mon, Apr 30, 2012 at 12:37 PM, Boris Partensky
> <boris.partensky@gmail.com> wrote:
>> 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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