Add inline shortcode support

An inline shortcode's name must end with `.inline`, all lowercase.

E.g.:

```bash
{{< time.inline >}}{{ now }}{{< /time.inline >}}
```

The above will print the current date and time.

Note that an inline shortcode's inner content is parsed and executed as a Go text template with the same context as a regular shortcode template.

This means that the current page can be accessed via `.Page.Title` etc. This also means that there are no concept of "nested inline shortcodes".

The same inline shortcode can be reused later in the same content file, with different params if needed, using the self-closing syntax:

```
{{< time.inline />}}
```

Fixes #4011

1 files changed, 30 insertions, 26 deletions

diff --git a/hugolib/site.go b/hugolib/site.go
index fb32853e3..25eb34f05 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -124,6 +124,8 @@ type Site struct {
 
 	disabledKinds map[string]bool
 
+	enableInlineShortcodes bool
+
 	// Output formats defined in site config per Page Kind, or some defaults
 	// if not set.
 	// Output formats defined in Page front matter will override these.
@@ -194,21 +196,22 @@ func (s *Site) isEnabled(kind string) bool {
 // reset returns a new Site prepared for rebuild.
 func (s *Site) reset() *Site {
 	return &Site{Deps: s.Deps,
-		layoutHandler:       output.NewLayoutHandler(),
-		disabledKinds:       s.disabledKinds,
-		titleFunc:           s.titleFunc,
-		relatedDocsHandler:  newSearchIndexHandler(s.relatedDocsHandler.cfg),
-		siteRefLinker:       s.siteRefLinker,
-		outputFormats:       s.outputFormats,
-		rc:                  s.rc,
-		outputFormatsConfig: s.outputFormatsConfig,
-		frontmatterHandler:  s.frontmatterHandler,
-		mediaTypesConfig:    s.mediaTypesConfig,
-		Language:            s.Language,
-		owner:               s.owner,
-		publisher:           s.publisher,
-		siteConfig:          s.siteConfig,
-		PageCollections:     newPageCollections()}
+		layoutHandler:          output.NewLayoutHandler(),
+		disabledKinds:          s.disabledKinds,
+		titleFunc:              s.titleFunc,
+		relatedDocsHandler:     newSearchIndexHandler(s.relatedDocsHandler.cfg),
+		siteRefLinker:          s.siteRefLinker,
+		outputFormats:          s.outputFormats,
+		rc:                     s.rc,
+		outputFormatsConfig:    s.outputFormatsConfig,
+		frontmatterHandler:     s.frontmatterHandler,
+		mediaTypesConfig:       s.mediaTypesConfig,
+		Language:               s.Language,
+		owner:                  s.owner,
+		publisher:              s.publisher,
+		siteConfig:             s.siteConfig,
+		enableInlineShortcodes: s.enableInlineShortcodes,
+		PageCollections:        newPageCollections()}
 
 }
 
@@ -282,17 +285,18 @@ func newSite(cfg deps.DepsCfg) (*Site, error) {
 	}
 
 	s := &Site{
-		PageCollections:     c,
-		layoutHandler:       output.NewLayoutHandler(),
-		Language:            cfg.Language,
-		disabledKinds:       disabledKinds,
-		titleFunc:           titleFunc,
-		relatedDocsHandler:  newSearchIndexHandler(relatedContentConfig),
-		outputFormats:       outputFormats,
-		rc:                  &siteRenderingContext{output.HTMLFormat},
-		outputFormatsConfig: siteOutputFormatsConfig,
-		mediaTypesConfig:    siteMediaTypesConfig,
-		frontmatterHandler:  frontMatterHandler,
+		PageCollections:        c,
+		layoutHandler:          output.NewLayoutHandler(),
+		Language:               cfg.Language,
+		disabledKinds:          disabledKinds,
+		titleFunc:              titleFunc,
+		relatedDocsHandler:     newSearchIndexHandler(relatedContentConfig),
+		outputFormats:          outputFormats,
+		rc:                     &siteRenderingContext{output.HTMLFormat},
+		outputFormatsConfig:    siteOutputFormatsConfig,
+		mediaTypesConfig:       siteMediaTypesConfig,
+		frontmatterHandler:     frontMatterHandler,
+		enableInlineShortcodes: cfg.Language.GetBool("enableInlineShortcodes"),
 	}
 
 	return s, nil