[FREEMARKER-84] Improve include directive to detect whether template exists

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Implemented
• Affects Version/s: 2.3.27-incubating
• Fix Version/s: 2.3.28
• Component/s: engine
• Assignee: Unassigned
• Reporter: Yanming Zhou
• Created: 10/Nov/17 08:02
• Updated: 05/Apr/18 11:48
• Resolved: 01/Mar/18 09:06

Description

I requested feature `ignore_missing=true` of <#include> and freemarker have implemented it, but it cannot handle fallback like

<#assign path="relative.ftl">
<#if isTemplatePresent(path)>
<#include path>
<#else>
template "${path}" is not exists
</#if>

Proposal 1:
Introduce a new special variable like "template_included" similar to "$?" of shell exit code

<#include path ignore_missing=true>
<#if !.template_included>
template "${path}" is not exists
</#if>

Proposal 2:
Add an argument like "template_included" for include directive

<#include path ignore_missing=true template_included="pathExists">
<#if !pathExists>
template "${path}" is not exists
</#if>

Proposal 3:
Introduce a new special directive such as <#missing> similar to html <noscript> tag

<#include path>
<#missing>
template "${path}" is not exists
</#missing>
</#include>