safeService

[nvx]

At the moment, using the service function when there are no healthy services available can result in unexpected behaviour, for example the following are given usage examples in the readme:

{{ range service "web" }}
server {{ .Name }} {{ .Address }}:{{ .Port }}{{ end }}

{{ with service "foo" }}
{{ with index . 0 }}
{{ .Node }}{{ end }}{{ end }}

In the event that there is no healthy service named web or foo, the first would result in a rendered file with no "server" statement, and the latter would result in a rendered file with no nodes listed.

In some instances the preferred behaviour would be to not render the file at all, ie, replicating the behaviour of safeTree or safeLs (if I'm understanding how they work anyway).

The obvious approach to make this work without a new function would be something like this:

{{ with index (service "foo") 0 }}
# ...
{{ end }}

But unfortunately this fails as per the documentation due to the multi-phase execution templates must account for the empty case.

Thoughts around adding a safeService function that prevents rendering unless at least one instance is returned?