Add description of linked issue to ticket's current description

[Ben Greene]

Essentially I am trying to build a system where one ticket compiles the description of other tickets that are marked with a special field and are moved to done into one big summary ticket. 
How would I access the linked issue's description?
Also side note would <br/> work for separating the new imported text from the previous text?

[Ben Greene · Accepted solution]

After some trial and error and a bit of guess work turns out I can access it using {{triggerIssue.description}}

[wwalser]

I'm not sure I've understood the use case perfectly. You may need to break the problem down into more discrete units so that I can understand more clearly.

> …one ticket compiles…

How does one go about locating this ticket into which things are compiled?

> …the description of other tickets that are marked with a special field…

How does one go about finding those other tickets?

When are you trying to perform this action?

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From the image you provided it seems like you want to do this when a ticket is transitioned to done. The way I am imagining it works is as follows:

When a ticket, tickets β, in project λ is closed, I want to add its description to a running list of all closed ticket descriptions. The list of closed ticket descriptions is maintained inside of ticket β′, [which is linked to ticket β via the relation "is caused by" | which is the parent of ticket β].

To accomplish this, you'd just need to alter the existing rule by adding an action inside of the branch that alters the description of ticket β′ to contain:

{{issue.description}}
{{triggerIssue.description}}

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> Also side note would <br/> work for separating the new imported text from the previous text?

You should just be able to use a standard return to separate the content. No need for markup to achieve this.

> After some trial and error and a bit of guess work turns out I can access it using {{triggerIssue.description}}

At the bottom of the branch component, and many other components, there is an expandable help info: "What issue data can I access in conditions and actions for related issues?". It contains helpful information like this: "You can however also access the issue that triggered this automation rule via {{triggerIssue}} (e.g. {{triggerIssue.fields.summary}})."

[Ben Greene]

Thanks for your answer but I have at this point got it working.

I indeed did use {{triggerIssue.description}}, but I would like to note that the page I was taken to with the help url did not list triggerIssue. I ended up guessing the variable name by putting it together from destinationIssue (which was listed on the help page) and seeing that another trigger spoke about a 'trigger issue'.