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

4 files changed, 50 insertions, 6 deletions

diff --git a/hugolib/paths/baseURL.go b/hugolib/paths/baseURL.go
index 9cb5627ba..de36c8636 100644
--- a/hugolib/paths/baseURL.go
+++ b/hugolib/paths/baseURL.go
@@ -27,13 +27,21 @@ type BaseURL struct {
 }
 
 func (b BaseURL) String() string {
-	return b.urlStr
+	if b.urlStr != "" {
+		return b.urlStr
+	}
+	return b.url.String()
 }
 
 func (b BaseURL) Path() string {
 	return b.url.Path
 }
 
+// HostURL returns the URL to the host root without any path elements.
+func (b BaseURL) HostURL() string {
+	return strings.TrimSuffix(b.String(), b.Path())
+}
+
 // WithProtocol returns the BaseURL prefixed with the given protocol.
 // The Protocol is normally of the form "scheme://", i.e. "webcal://".
 func (b BaseURL) WithProtocol(protocol string) (string, error) {
diff --git a/hugolib/paths/baseURL_test.go b/hugolib/paths/baseURL_test.go
index af1d2e38d..382a18314 100644
--- a/hugolib/paths/baseURL_test.go
+++ b/hugolib/paths/baseURL_test.go
@@ -58,4 +58,9 @@ func TestBaseURL(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, "", b.String())
 
+	// BaseURL with sub path
+	b, err = newBaseURLFromString("http://example.com/sub")
+	require.NoError(t, err)
+	require.Equal(t, "http://example.com/sub", b.String())
+	require.Equal(t, "http://example.com", b.HostURL())
 }
diff --git a/hugolib/paths/paths.go b/hugolib/paths/paths.go
index cf8792e5a..3be034fef 100644
--- a/hugolib/paths/paths.go
+++ b/hugolib/paths/paths.go
@@ -39,11 +39,14 @@ type Paths struct {
 	// Directories
 	// TODO(bep) when we have trimmed down mos of the dirs usage outside of this package, make
 	// these into an interface.
-	ContentDir      string
-	ThemesDir       string
-	WorkingDir      string
+	ContentDir string
+	ThemesDir  string
+	WorkingDir string
+
+	// Directories to store Resource related artifacts.
 	AbsResourcesDir string
-	AbsPublishDir   string
+
+	AbsPublishDir string
 
 	// pagination path handling
 	PaginatePath string
@@ -79,12 +82,21 @@ func New(fs *hugofs.Fs, cfg config.Provider) (*Paths, error) {
 		return nil, fmt.Errorf("Failed to create baseURL from %q: %s", baseURLstr, err)
 	}
 
-	// TODO(bep)
 	contentDir := cfg.GetString("contentDir")
 	workingDir := cfg.GetString("workingDir")
 	resourceDir := cfg.GetString("resourceDir")
 	publishDir := cfg.GetString("publishDir")
 
+	if contentDir == "" {
+		return nil, fmt.Errorf("contentDir not set")
+	}
+	if resourceDir == "" {
+		return nil, fmt.Errorf("resourceDir not set")
+	}
+	if publishDir == "" {
+		return nil, fmt.Errorf("publishDir not set")
+	}
+
 	defaultContentLanguage := cfg.GetString("defaultContentLanguage")
 
 	var (
@@ -183,6 +195,21 @@ func (p *Paths) Themes() []string {
 	return p.themes
 }
 
+func (p *Paths) GetTargetLanguageBasePath() string {
+	if p.Languages.IsMultihost() {
+		// In a multihost configuration all assets will be published below the language code.
+		return p.Lang()
+	}
+	return p.GetLanguagePrefix()
+}
+
+func (p *Paths) GetURLLanguageBasePath() string {
+	if p.Languages.IsMultihost() {
+		return ""
+	}
+	return p.GetLanguagePrefix()
+}
+
 func (p *Paths) GetLanguagePrefix() string {
 	if !p.multilingual {
 		return ""
diff --git a/hugolib/paths/paths_test.go b/hugolib/paths/paths_test.go
index 6cadc747f..3bd445b8b 100644
--- a/hugolib/paths/paths_test.go
+++ b/hugolib/paths/paths_test.go
@@ -30,6 +30,10 @@ func TestNewPaths(t *testing.T) {
 	v.Set("defaultContentLanguageInSubdir", true)
 	v.Set("defaultContentLanguage", "no")
 	v.Set("multilingual", true)
+	v.Set("contentDir", "content")
+	v.Set("workingDir", "work")
+	v.Set("resourceDir", "resources")
+	v.Set("publishDir", "public")
 
 	p, err := New(fs, v)
 	assert.NoError(err)