I have a template that can optionally be prefixed with some string prefix. This prefix itself does not end with a newline character but can optionally contain newline characters (e.g. hello world, hello\nworld, ...). In the template, the newline is added and then the contents are rendered. If the prefix is the empty string, the rendered template immediately starts with the contents:

{{- with $.Prefix -}}
{{ . }}
{{ end -}}
Contents

Examples of what I want to achieve:

Prefix="Hello World":

Hello World
Contents

Prefix="Hello\nWorld:

Hello
World
Contents

Prefix="":

Contents

However, due to the trailing hyphen in {{ end -}}, when the prefix is set it renders as:

Hello WorldContents

But moving the hyphen to the start {{- end }} fails to render the template when the prefix is not set:

Contents

My interpretation of how the hyphens should be executed is that the leading hyphen removes whitespace before the pipeline contents and vice-versa for after but somehow the newline contained in the $.Prefix block is removed by the trailing hyphen. How should I correct this?

I have a template that can optionally be prefixed with some string prefix. This prefix itself does not end with a newline character but can optionally contain newline characters (e.g. hello world, hello\nworld, ...). In the template, the newline is added and then the contents are rendered. If the prefix is the empty string, the rendered template immediately starts with the contents:

{{- with $.Prefix -}}
{{ . }}
{{ end -}}
Contents

Examples of what I want to achieve:

Prefix="Hello World":

Hello World
Contents

Prefix="Hello\nWorld:

Hello
World
Contents

Prefix="":

Contents

However, due to the trailing hyphen in {{ end -}}, when the prefix is set it renders as:

Hello WorldContents

But moving the hyphen to the start {{- end }} fails to render the template when the prefix is not set:

Contents

My interpretation of how the hyphens should be executed is that the leading hyphen removes whitespace before the pipeline contents and vice-versa for after but somehow the newline contained in the $.Prefix block is removed by the trailing hyphen. How should I correct this?

• go
• templates
• go-templates

• Your newline needs to be conditional. Only if $.Prefix is not empty do you want to include a newline. No single template formatting is going to take care of both those cases. – erik258 Commented Nov 28, 2024 at 14:12
• exactly, it works as intended with Go 1.23.3 – Arkadiusz Drabczyk Commented Nov 28, 2024 at 21:47

1 Answer 1

As the commenters (Cerise, Arkadiusz) pointed out, the example works and the issue was caused elsewhere by it being rendered as a nested template in a (complex) set of other template(s) which itself had incorrect hyphens. Rendering it before posting in the playground would have caught the wrong conclusion being drawn from the outputs of the tests.

Leaving this question up for others working with go-templates.