Why does the tag provider crash with this expression?

Ignition
1

Hi, I am using an expression tag in ignition. In the expression I have written is:
" tag("[.]") "
This makes the tag provider become unavailable.
Is this because of some kind of infinite loop?

2

Yes.

3

What result were you hoping for with that expression?

4

The expression is not finished, but since it crashed, I gave up doing it that way.
What I actually wanted was to read the value of a tag in the same folder. The plan was to do something like:
tag("[.]/../siblingTag")
But I did not get it to work.
I need to use a string for the relative path to be able to change it through code later.

5

What version of Ignition are you using? I can't reproduce a crash or infinite loop.

6

I am using Ignition 8.1.27
The datatype was string.
What about this expression: tag("[.]/..")

7

No, same nonsense value, but no crash:

image

8

This is what the error looks like when the expression is tag("[.]"):
CrashInTagprovider_Zoomed

9

Try using this UDT:
{
"name": "testUDT",
"tagType": "UdtType",
"tags": [
{
"valueSource": "reference",
"name": "New Tag",
"tagType": "AtomicTag"
}
]
}

And this instance of it:
{
"name": "New Instance",
"typeId": "testUDT",
"tagType": "UdtInstance",
"tags": [
{
"valueSource": "expr",
"expression": "tag("[.]")",
"dataType": "String",
"name": "New Tag",
"tagType": "AtomicTag"
}
]
}

10

Ok, that your expression tag was nested in a UDT instance was a relevant detail.

I'll file a bug report.

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