Custom JMeter Functions plugin is not detected if jmx file contains any of its functions

**eR@SeR** ([Bug 65116](https://bz.apache.org/bugzilla//show_bug.cgi?id=65116&redirect=false)):
Hello,

If jmx file contains any of the Custom JMeter Functions like "doubleSum", "if", "base64Encode" etc. but the plugin is not previously installed by JMeter plugins manager, an error pop up message is not shown like for other missing plugins. If JMeter plugins manager is put in lib/ext folder, and when jmx file is opened which contains one or more of its functions, it doesn't detect that plugin should be installed and therefore functions are not evaluated when test is run. Check jmx example in the attachment.

Expected:

Pop up error message is shown that Custom JMeter functions are detected in jmx file. If JMeter plugins manager is in lib/ext folder, suggest the installation of Custom JMeter functions.

Or

All Custom JMeter functions can be merged to be part of JMeter core functions. I vote for the latter.

Custom JMeter functions link https://jmeter-plugins.org/wiki/Functions/

Jmeter 5.5 ff9866a
Microsoft Windows 10 Enterprise 64-bit
java version "14.0.1" 2020-04-14

Created attachment [customJMeterFunctions.jmx](https://apache.github.io/jmeter-bugzilla-attachments/16/65116/37722/customJMeterFunctions.jmx): customJMeterFunctions.jmx
customJMeterFunctions.jmx

````xml

false
true
false







continue

false
1

1
1
false


true



false

saveConfig

true
true
true
true
true
true
true
true
true
false
true
true
false
false
false
true
false
false
false
true
0
true
true
true
true
true
true






true


true
groovy



true


true
groovy



true


true
groovy



true


true
groovy

````

Version: Nightly
Severity: normal
OS: All