Trim Self

Remove trailing newline and leading indent on tags that do not replace itself with content, only if the tag appears on its own line*.

Similar to autoTrim, but does not trim aggressively. In effect, it makes tags such as [/]function, [/]if, and other tags that do not get replaced with content (such as echo), appear as though they were not there.

This plugin exists to enable auto-trimming work as expected when vento is used for file formats where whitespace is significant, such as markdown, unlike HTML.

How it works

For such tags that are on a line of its own, ie:

• Has optional leading indents preceded directly by a newline, AND
• Either EOF or a newline after it.

Then, only these kind of whitespace are removed:

• Spaces and tabs, preceded by a single newline on its left – ie, indent – replaced by a newline, in other words, dedented.
• One trailing newline on this kind of tags, this single \n OR \r\n is removed;

No other kind of whitespace around such tags are removed, unlike autoTrim.

Table of contents:

• Example
• Why trim-self when we already have auto-trim?
• Setup
  • Vento example
  • Lume example
• Usage
• TODO

Example

Template:

<p>
  Text before.
  {{ set name = "world" }}
  Hello, {{ name }}!
</p>

Without trim-self:

<p>
  Text before
__
  Hello, world!
</p>

Trailing spaces represented as _.

After trim-self:

<p>
  Text before.
  Hello, {{ name }}!
</p>

Here’s the step-by-step transformation for the {{ set ... }} tag:

1. <p>
     Text before.
     {{ set name = "world" }}
     Hello, {{ name }}!
   </p>

2. <p>
     Text before.
     {{ set name = "world" }}  Hello, {{ name }}!
   </p>

3. <p>
     Text before.
   {{ set name = "world" }}  Hello, {{ name }}!
   </p>

4. After vento’s processing:

   <p>
     Text before.
     Hello, {{ name }}!
   </p>

   <p>
     Text before.
     Hello, world!
   </p>

Check out the tests for self-documenting examples.

Why trim-self when we already have auto-trim?

Auto-trim does a great job at doing what it’s supposed to do, but both auto-trim and the built in trimming functionality (similar to Go templates), remove whitespace too aggressively.

For instance, consider this template:

Inline{{ if true }} test{{ /if }}
- {{ if true }}List item.{{ else }}Other list item.{{ /if }}
Some text after.

With autoTrim, it would be transformed into:

Inline test-List item.Some text after.

Trim-self does what you expect out of a plugin that will simply “make template tags produce code such that it was as though they weren’t there.”

Inline test
- List item.
Some text after.

Furthermore, autoTrim will remove trailing spaces followed by a newline, while this may desirable in general, trimSelf does not do this because this functionality should be delegated to editors and tooling.

Setup

Vento example

import trimSelf from "https://deno.land/x/vento_plugin_trim_self/mod.ts"

env.use(trimSelf());

Lume example

// _config.ts / _config.js
import lume from "lume/mod.ts";
import vento from "lume/plugins/vento.ts";
import trimSelf from "https://deno.land/x/vento_plugin_trim_self/mod.ts";

const site = lume();
site.use(vento({
  plugins: [trimSelf()],
  options: {},
}))

export default site;

Usage

Trim-self does its job automatically.

TODO

Filters are not yet supported:

{{ for item in list |> myFilter }}
<!-- the newline after the above tag will not be trimmed -->
{{ /for }}

Support filters, by binding them to the left most (but closest) tag. Or at least add docs on how to workaround this, i.e., in Lume, use site.data("myFilter", fn) rather than site.filter("myFilter", fn) and use it as myFilter(list) instead.