Item9480: Foswiki::_renderZone() sometimes renders body/head multiple times

Kenneth pointed out that usage of RenderFormPlugin, which calls JSCalendarContrib::addHEAD multiple times, results in JSCalendarContrib's add's being added to both body and head zones.

This only happens for {OptimizePageLayout} = 0;

-- PaulHarvey - 17 Aug 2010

1. The page is built. Foswiki::writeCompletePage() is dispatched.
   1. A call to Foswiki::_renderZones() is made.
      1. Foswiki::_renderZones() calls Foswiki::_renderZone() for the head zone.
         • When {OptimizePageLayout} = 0; - then this usually renders/flushes both head and body zones
         1. Foswiki::_renderZone() calls Foswiki::Meta::renderTML()
         2. Foswiki::Meta::renderTML() causes RenderFormPlugin::postRenderHandler() to be dispatched
         3. RenderFormPlugin::postRenderHandler() calls Foswiki::Func::addToZone() to add content to both head and body zones
      2. Foswiki::_renderZones() calls Foswiki::_renderZone() for the body zone.
         1. When {OptimizePageLayout} = 0;, normally the body zone is empty. But we render/flush both head and body zones again - and this time there is the content added by RenderFormPlugin::postRenderHandler(), again.

Options:

1. Fix RenderFormPlugin. It should be doing this stuff in initPlugin, not abusing writeCompletePage() (I think this is a pre-ADDTOZONE technique)
2. Give Foswiki::_renderZones() some special logic to detect {OptimizePageLayout} = 0; and not call _renderZone(body) in the first place
3. Add some sort of counter/state/flag to Foswiki::_renderZone() to really ensure body/head zones are only rendered once? No, that's a terrible idea.

Options 1 & 2 seem reasonable to me. Opinions?

-- PaulHarvey - 18 Aug 2010

I added a fix which only caters for the body, head, and {OptimizePageLayout} = 0 case.

It's possible that plugins working on their own non-body/head zones could come up against this bug in the same way.

A proper solution might involve new plugin hooks - beforeRenderZone/afterRenderZone, maybe - and a rethink of a what point in the rendering pipeline we call renderTML/expandMacros

-- PaulHarvey - 18 Aug 2010

added Development.AddToZoneFromPluginHandlers

-- PaulHarvey - 18 Aug 2010

Re-opened to fix a silly mistake affect body zone rendering with {OptimizePageLayout} = 1

-- PaulHarvey - 22 Aug 2010

Re-opened again to fix the tests :/

-- PaulHarvey - 23 Aug 2010

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