Cannot use escape on output of smarty defined function

There seems to be a big difference between how smarty handles filtering of smarty defined functions. Which breaks on newer versions of smarty.

It seems that smarty no longer escapes javascript properly, if function is called.

Workaround: Assign output to variable (by capture for example) and escape:'javascript' works properly again.

Disadvantages of behavior:

• Need to introduce another variable
• Backward compatibility

Example code

{function name=testfunction index=0 el=''}
    ---
    Line1 "das" asd as ' asddass' " '' "
    Line2
    ---
{/function}
Call
{testfunction}
Call:escape
{testfunction|escape}
Call:escape:'javascript'
{testfunction|escape:'javascript'}

Output on older smarty: const SMARTY_VERSION = 'Smarty-3.1.19';

Call
    ---
    Line1 "das" asd as ' asddass' " '' "
    Line2
    ---

Call:escape
    ---
    Line1 "das" asd as ' asddass' " '' "
    Line2
    ---
Call:escape:'javascript'
    ---\n    Line1 \"das\" asd as \' asddass\' \" \'\' \"\n    Line2\n    ---\n

Output on new smarty
v3.1.30 - raw installed smarty
and 3.1.43 - bundled with Prestashop 1.7

---
    Line1
    Line2
---

Call:escape

---
    Line1
    Line2
---

Call:escape:'javascript'

---
    Line1
    Line2
---

Example workaround

{capture name=myvarname}
    {testfunction}
{/capture}
{$smarty.capture.myvarname|escape:'javascript'}

Start with the Smarty defined-function example and compare how {testfunction|escape} and {testfunction|escape:'javascript'} are processed in the reported older and newer versions. Reproduce the output difference, then trace the defined-function and escaping behavior. Done means direct escaping matches the expected escaped output without requiring capture.