Skip template if a referenced variable is missing?

[cyqsimon]

As stated, I am trying to create a template file that references a few user-defined variables. But when any one of these necessary variables are unset, I wish for chezmoi to skip the file (and perhaps emit a warning) instead of hard-erroring.

Is this something chezmoi supports? If not please treat this as a feature request.

P.s. I'm not terribly familiar with go templating, so maybe there is already a built-in way to do this that I'm not aware of. Anyways, please enlighten me.

[twpayne]

You can use the missing-key template directive:

{{/* chezmoi:template:missing-key=zero */}}

Alternatively, you can set this globally by setting template.options in your configuration file:

[template]
    options = ["missing-key=zero"]

[halostatue]

Note that this won't skip the file (that can't be done without structuring your file to be empty if the values are missing), but it's the way that Go templates work.

[cyqsimon]

Thanks for the swift response.

This is not exactly what I'm looking for. Currently, both zero and invalid still cause the file to be generated, just with the placeholder value set to <no value>. What I really want is for the "instantiated file" (to borrow an OOP terminology) to not appear at all when any key specified in the template is missing.

Could you consider adding such a mode to missing-key that does this? Perhaps skip-file? If this is not possible or very difficult due to technical reasons I'd like to know too.

Edit: sorry, took a long while to type out my comment; didn't see your follow up.

[cyqsimon]

My specific use case is that I've got a main configuration file foo.conf, and a drop-in directory foo.conf.d. (This is a relatively common pattern in things like systemd, haproxy, dnsmasq, etc.) One of the drop-in files foo.conf.d/enable-feature-a.conf has a field that is a per-machine key, without which the other configuration options in this file are invalid, and will cause foo to error on launch.

So my intention is to make enable-feature-a.conf a template: when I specify a value for the variable feature_a_key, foo.conf.d/enable-feature-a.conf is instantiated and the feature is available. But on machines where this feature is not required, I can leave feature_a_key undeclared, so that foo.conf.d/enable-feature-a.conf does not appear, and the program still works, just without feature_a.

[halostatue]

Right. The mode you want won't work because this is a feature of go templating. However, you can do this (a) without missing-key=zero and (b) without this feature:

{{- $feature_a_key := (get . "feature_a_key") -}}
{{- if $feature_a_key -}}
# contents of enable-feature-a.conf, just use `$feature_a_key` instead of `.feature_a_key`
{{- end -}}

Unless you have the empty_ attribute set (foo.conf.d/empty_enable-feature-a.conf.tmpl), chezmoi will not create files that evaluate to empty contents, but they have to be completely empty (no whitespace or anything).

If there are multiple values to possibly check, you can easily do this with if or $a $b $c $d $e…; if all of them must be true, then if and $a $b $c $d $e….

[cyqsimon]

The mode you want won't work because this is a feature of go templating.

Okay yeah. I understand.

However, you can do this (a) without missing-key=zero and (b) without this feature:

I suspected this is a possibility, but I wanted to see if there is a simpler solution first. Thanks for showing exactly how to do it though.

If there are multiple values to possibly check, you can easily do this with if or $a $b $c $d $e…; if all of them must be true, then if and $a $b $c $d $e….

You preempted my next question. 👍

I'll try out your recommendation and get back to you.

[cyqsimon]

Yep your recommendation works as expected. This is what I ended up with, after changing out get for dig:

{{- $key0 := (dig "foo" "key0" nil .) -}}
{{- $key1 := (dig "foo" "key1" nil .) -}}
{{- if and $key0 $key1 -}}
key0 = {{ $key0 }}
key1 = {{ $key1 }}
{{ end -}}

It's a bit cumbersome but it works. Thanks again!

[twpayne]

If you want the template to give an error then you can use the fail template function, e.g.:

{{- $key0 := (dig "foo" "key0" nil .) -}}
{{- $key1 := (dig "foo" "key1" nil .) -}}
{{- if and $key0 $key1 -}}
key0 = {{ $key0 }}
key1 = {{ $key1 }}
{{- else -}}
{{- fail "Both key0 and key1 must be set" -}}
{{ end -}}

You'll have to do this manually for each template however. There is no global setting.