Add Hugo Piper with SCSS support and much more

Before this commit, you would have to use page bundles to do image processing etc. in Hugo.

This commit adds

* A new `/assets` top-level project or theme dir (configurable via `assetDir`)
* A new template func, `resources.Get` which can be used to "get a resource" that can be further processed.

This means that you can now do this in your templates (or shortcodes):

```bash
{{ $sunset := (resources.Get "images/sunset.jpg").Fill "300x200" }}
```

This also adds a new `extended` build tag that enables powerful SCSS/SASS support with source maps. To compile this from source, you will also need a C compiler installed:

```
HUGO_BUILD_TAGS=extended mage install
```

Note that you can use output of the SCSS processing later in a non-SCSSS-enabled Hugo.

The `SCSS` processor is a _Resource transformation step_ and it can be chained with the many others in a pipeline:

```bash
{{ $css := resources.Get "styles.scss" | resources.ToCSS | resources.PostCSS | resources.Minify | resources.Fingerprint }}
<link rel="stylesheet" href="{{ $styles.RelPermalink }}" integrity="{{ $styles.Data.Digest }}" media="screen">
```

The transformation funcs above have aliases, so it can be shortened to:

```bash
{{ $css := resources.Get "styles.scss" | toCSS | postCSS | minify | fingerprint }}
<link rel="stylesheet" href="{{ $styles.RelPermalink }}" integrity="{{ $styles.Data.Digest }}" media="screen">
```

A quick tip would be to avoid the fingerprinting part, and possibly also the not-superfast `postCSS` when you're doing development, as it allows Hugo to be smarter about the rebuilding.

Documentation will follow, but have a look at the demo repo in https://github.com/bep/hugo-sass-test

New functions to create `Resource` objects:

* `resources.Get` (see above)
* `resources.FromString`: Create a Resource from a string.

New `Resource` transformation funcs:

* `resources.ToCSS`: Compile `SCSS` or `SASS` into `CSS`.
* `resources.PostCSS`: Process your CSS with PostCSS. Config file support (project or theme or passed as an option).
* `resources.Minify`: Currently supports `css`, `js`, `json`, `html`, `svg`, `xml`.
* `resources.Fingerprint`: Creates a fingerprinted version of the given Resource with Subresource Integrity..
* `resources.Concat`: Concatenates a list of Resource objects. Think of this as a poor man's bundler.
* `resources.ExecuteAsTemplate`: Parses and executes the given Resource and data context (e.g. .Site) as a Go template.

Fixes #4381
Fixes #4903
Fixes #4858

1 files changed, 4 insertions, 4 deletions

diff --git a/hugolib/site_render.go b/hugolib/site_render.go
index e837d9f0b..5efe6badc 100644
--- a/hugolib/site_render.go
+++ b/hugolib/site_render.go
@@ -252,7 +252,7 @@ func (s *Site) renderRSS(p *PageOutput) error {
 	limit := s.Cfg.GetInt("rssLimit")
 	if limit >= 0 && len(p.Pages) > limit {
 		p.Pages = p.Pages[:limit]
-		p.Data["Pages"] = p.Pages
+		p.data["Pages"] = p.Pages
 	}
 
 	layouts, err := s.layoutHandler.For(
@@ -279,7 +279,7 @@ func (s *Site) render404() error {
 	p := s.newNodePage(kind404)
 
 	p.title = "404 Page not found"
-	p.Data["Pages"] = s.Pages
+	p.data["Pages"] = s.Pages
 	p.Pages = s.Pages
 	p.URLPath.URL = "404.html"
 
@@ -326,7 +326,7 @@ func (s *Site) renderSitemap() error {
 	page.Sitemap.Priority = sitemapDefault.Priority
 	page.Sitemap.Filename = sitemapDefault.Filename
 
-	n.Data["Pages"] = pages
+	n.data["Pages"] = pages
 	n.Pages = pages
 
 	// TODO(bep) we have several of these
@@ -369,7 +369,7 @@ func (s *Site) renderRobotsTXT() error {
 	if err := p.initTargetPathDescriptor(); err != nil {
 		return err
 	}
-	p.Data["Pages"] = s.Pages
+	p.data["Pages"] = s.Pages
 	p.Pages = s.Pages
 
 	rLayouts := []string{"robots.txt", "_default/robots.txt", "_internal/_default/robots.txt"}