What is, and what use cases have the dot "." in helm charts? - kubernetes

Question

im currently going through the docs of helm, and there have been at least 3 different uses for the dot (.), is there any specific definition for it? and does it have something in common with the bash use (actual folder/files)?
some cases in the documentation
This print the accesed files in the range called before?
{{- $files := .Files }}
{{- range tuple "config1.toml" "config2.toml" "config3.toml" }}
{{ . }}: |-
{{ $files.Get . }}
{{- end }}
This tells "mychart.app" to use the files in the current folder (bash-like behaviour)
{{ include "mychart.app" . | indent 4 }}
and this, i guess it takes the values from the whole folder??? i guess this is not correct since is not working (it has been made by another employee back then and i have to fix it)
{{- define "read.select-annot" -}}
{{- range $key, $value := . }}
{{ $key }}: {{ $value }}
{{- end }}
{{- end }}
thanks for the help

Answer 1

In general, . in Helm templates has nothing to do with files or directories.
The Helm templating language uses Go's text/template system. There are a couple of different ways a period character can appear there.
First of all, . can be a character in a string:
{{- range tuple "config1.toml" "config2.toml" "config3.toml" }}
{{/* ^^^^^^^^^^^^
this is a literal string "config1.toml" */}}
...
{{- end }}
Secondly, . can be a lookup operator. There aren't any solid examples in your question, but a typical use is looking up in values. If your values.yaml file has
root:
key: value
then you can expand
{{ .Values.root.key }}
and the . before root and key navigates one level down in the dictionary structure.
The third use, and possibly the one that's confusing you, is that . on its own is a variable.
{{ . }}
You can do field lookups on it, and you have some examples of that: .Files is the same as index . "Files", and looks up the field "Files" on the object ..
You use . as a variable in several places:
{{- $files := .Files }} {{/* Get "Files" from . */}}
{{ . }} {{/* Write . as a value */}}
{{ include "mychart.app" . }} {{/* Pass . as the template parameter */}}
. is tricky in that it has somewhat contextual meaning:
At the top level, Helm initializes . to an object with keys Files, Release, Values, and Chart.
In a defined template, . is the parameter to the template. (So when you include or template, you need to pass . down as that parameter.)
In a range loop, . is the current item being iterated on.
In a with block, . is the matched item if it exists.
In particular, the interaction with range can be tricky. Let's look at a simplified version of your loop:
# {{ . }}
{{- range tuple "config1.toml" "config2.toml" "config3.toml" }}
- {{ . }}
{{- end }}
Outside the range loop, . is probably the top-level Helm object. But inside the range loop, . is the file name (each value from the tuple in turn). That's where you need to save values from . into local variables:
{{/* We're about to invalidate ., so save .Files into a variable. */}}
{{- $files := .Files }}
{{- range tuple "config1.toml" "config2.toml" "config3.toml" }}
{{/* This . is the filename from the "tuple" call */}}
{{ . }}: |-
{{/* Call .Get, from the saved $files, passing the filename .
as the parameter */}}
{{ $files.Get . }}
{{- end }}