helm getting subchart service names

Question

Whats the best way to get the helm subchart service names to reference into my ingress controller that will sit in the parent chart

values.yaml
---
ingress:
  paths:
    - serviceName: app-1
      path: /app-1/*
      port: 8080
    - serviceName: app-2
      path: /app-2/*
      port: 8080


ingress.yaml 
---
{{- range .Values.ingress.paths }}
          - path: {{ .path }}
            backend:
              {{- $subchart := .serviceName -}}
              serviceName: {{- include "$subchart.fullname" .}}
              servicePort: {{ .port }}
        {{- end }}

template: no template "$subchart.fullname" associated with template "gotpl"

Answer 1

helm 3.7 version has solved the problem https://github.com/helm/helm/pull/9957.
You can use like this

{{ template "bar.fullname" .Subcharts.bar }}

Answer 2

If the subchart uses the fullname function from _helpers.tpl (provided by helm by default for new charts) you can use this (replace postgresql with the name of the subchart):

{{- $fullName := include "postgresql.fullname" (mustMerge (dict "Chart" (dict "Name" "postgresql") "Values" .Values.postgresql) (deepCopy .)) -}}