Equivalent of Node.js' `path.relative`

[rnwst]

It would be convenient if Hugo's path functions included one that allowed us to make an absolute location relative to another absolute location, in the same way Node.js' path.relative function works. This could be called path.Rel, path.RelFromTo, path.Relative, or something along those lines.

[bep]

absolute location relative to another absolute location

There are very few (2?) absolute locations in Hugo's API, so you need to come up with some "useful examples".

[rnwst]

Thank you for considering my proposal! I should've been clearer in my proposal, by absolute location I meant absolute URL path, like those created with RESOURCE.RelPermalink. The return value of the function would be a relative URL path. As an example, path.RelFromTo "/js/a/a.js" "/js/b/b.js" would return "../../b/b.js".

As to a simple example where this could be used. A few bytes could be saved by including relative instead of absolute URL paths for page resources in templates, like so: src="{{ path.RelFromTo .RelRef $pageResource.RelPermalink }}" (since the resulting relative URL path would likely be much shorter than the equivalent absolute URL path). This is just a simple example where, admittedly, not much is gained, but it illustrates the function.

Here is another example, which is my personal use case. Apologies if this is too convoluted. I have a bunch of small module scripts which are all imported into a single module script, residing under assets/js/index-inline.js:

import './a.js';
import './lib/b.js';
import './dir1/dir2/c.js';

In production, I want to inline, bundle, and minify these, to increase page load speed. For development, however, I don't want to bundle and inline the imports, to make debugging easier. This means that for development, I need to pass the imports as externals to js.Build, and at the same time also as shims, to make sure the relative URL paths in the import statements of index-inline.js get replaced with the absolute URL paths of the fingerprinted and published imports.

{{- $inlinePath := "/js/index-inline.js" }}
{{- $inlineIndex := resources.Get $inlinePath }}
{{- $inlineBuildOpts := dict "format" "esm" }}
{{- if hugo.IsProduction }}
  {{- $inlineBuildOpts = merge $inlineBuildOpts (dict "minify" true) }}
{{- else }}
  {{- $modules := resources.Match "js/**.js" }}
  {{- $shims := dict }}
  {{- $externals := slice }}
  {{- range $modules }}
    {{- /* Generate both relative and absolute paths, as we cannot be sure how the modules were imported. */}}
    {{- $relPath := printf "%s/%s" "./" (path.RelFromTo $inlinePath .Name) }}
    {{- $absPath := .Name }}
    {{- $url := (fingerprint .).RelPermalink }}
    {{- $shims = merge $shims (dict $relPath $url
                                    $absPath $url) }}
    {{- $externals = append $externals (slice $url) }}
  {{- end }}
  {{- $inlineBuildOpts = merge $inlineBuildOpts (dict "shims" $shims
                                                      "externals" $externals) }}
{{- end }}
{{- $inlineIndex = $inlineIndex | js.Build $inlineBuildOpts }}
    <script type=module>
      {{ $inlineIndex.Content | safeJS }}
    </script>