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, 91 insertions, 25 deletions

diff --git a/hugolib/shortcode.go b/hugolib/shortcode.go
index 1860a5e90..8be312f83 100644
--- a/hugolib/shortcode.go
+++ b/hugolib/shortcode.go
@@ -18,6 +18,9 @@ import (
 	"errors"
 	"fmt"
 	"html/template"
+	"path"
+
+	"github.com/gohugoio/hugo/common/herrors"
 
 	"reflect"
 
@@ -163,13 +166,15 @@ func (scp *ShortcodeWithPage) page() *Page {
 const shortcodePlaceholderPrefix = "HUGOSHORTCODE"
 
 type shortcode struct {
-	name     string
-	inner    []interface{} // string or nested shortcode
-	params   interface{}   // map or array
-	ordinal  int
-	err      error
-	doMarkup bool
-	pos      int // the position in bytes in the source file
+	name      string
+	isInline  bool          // inline shortcode. Any inner will be a Go template.
+	isClosing bool          // whether a closing tag was provided
+	inner     []interface{} // string or nested shortcode
+	params    interface{}   // map or array
+	ordinal   int
+	err       error
+	doMarkup  bool
+	pos       int // the position in bytes in the source file
 }
 
 func (sc shortcode) String() string {
@@ -245,6 +250,8 @@ type shortcodeHandler struct {
 
 	placeholderID   int
 	placeholderFunc func() string
+
+	enableInlineShortcodes bool
 }
 
 func (s *shortcodeHandler) nextPlaceholderID() int {
@@ -259,11 +266,12 @@ func (s *shortcodeHandler) createShortcodePlaceholder() string {
 func newShortcodeHandler(p *Page) *shortcodeHandler {
 
 	s := &shortcodeHandler{
-		p:                  p.withoutContent(),
-		contentShortcodes:  newOrderedMap(),
-		shortcodes:         newOrderedMap(),
-		nameSet:            make(map[string]bool),
-		renderedShortcodes: make(map[string]string),
+		p:                      p.withoutContent(),
+		enableInlineShortcodes: p.s.enableInlineShortcodes,
+		contentShortcodes:      newOrderedMap(),
+		shortcodes:             newOrderedMap(),
+		nameSet:                make(map[string]bool),
+		renderedShortcodes:     make(map[string]string),
 	}
 
 	placeholderFunc := p.s.shortcodePlaceholderFunc
@@ -313,11 +321,26 @@ const innerNewlineRegexp = "\n"
 const innerCleanupRegexp = `\A<p>(.*)</p>\n\z`
 const innerCleanupExpand = "$1"
 
-func prepareShortcodeForPage(placeholder string, sc *shortcode, parent *ShortcodeWithPage, p *PageWithoutContent) map[scKey]func() (string, error) {
-
+func (s *shortcodeHandler) prepareShortcodeForPage(placeholder string, sc *shortcode, parent *ShortcodeWithPage, p *PageWithoutContent) map[scKey]func() (string, error) {
 	m := make(map[scKey]func() (string, error))
 	lang := p.Lang()
 
+	if sc.isInline {
+		key := newScKeyFromLangAndOutputFormat(lang, p.outputFormats[0], placeholder)
+		if !s.enableInlineShortcodes {
+			m[key] = func() (string, error) {
+				return "", nil
+			}
+		} else {
+			m[key] = func() (string, error) {
+				return renderShortcode(key, sc, nil, p)
+			}
+		}
+
+		return m
+
+	}
+
 	for _, f := range p.outputFormats {
 		// The most specific template will win.
 		key := newScKeyFromLangAndOutputFormat(lang, f, placeholder)
@@ -335,7 +358,34 @@ func renderShortcode(
 	parent *ShortcodeWithPage,
 	p *PageWithoutContent) (string, error) {
 
-	tmpl := getShortcodeTemplateForTemplateKey(tmplKey, sc.name, p.s.Tmpl)
+	var tmpl tpl.Template
+
+	if sc.isInline {
+		templName := path.Join("_inline_shortcode", p.Path(), sc.name)
+		if sc.isClosing {
+			templStr := sc.inner[0].(string)
+
+			var err error
+			tmpl, err = p.s.TextTmpl.Parse(templName, templStr)
+			if err != nil {
+				fe := herrors.ToFileError("html", err)
+				l1, l2 := p.posFromPage(sc.pos).LineNumber, fe.Position().LineNumber
+				fe = herrors.ToFileErrorWithLineNumber(fe, l1+l2-1)
+				return "", p.errWithFileContext(fe)
+			}
+
+		} else {
+			// Re-use of shortcode defined earlier in the same page.
+			var found bool
+			tmpl, found = p.s.TextTmpl.Lookup(templName)
+			if !found {
+				return "", _errors.Errorf("no earlier definition of shortcode %q found", sc.name)
+			}
+		}
+	} else {
+		tmpl = getShortcodeTemplateForTemplateKey(tmplKey, sc.name, p.s.Tmpl)
+	}
+
 	if tmpl == nil {
 		p.s.Log.ERROR.Printf("Unable to locate template for shortcode %q in page %q", sc.name, p.Path())
 		return "", nil
@@ -406,7 +456,16 @@ func renderShortcode(
 
 	}
 
-	return renderShortcodeWithPage(tmpl, data)
+	s, err := renderShortcodeWithPage(tmpl, data)
+
+	if err != nil && sc.isInline {
+		fe := herrors.ToFileError("html", err)
+		l1, l2 := p.posFromPage(sc.pos).LineNumber, fe.Position().LineNumber
+		fe = herrors.ToFileErrorWithLineNumber(fe, l1+l2-1)
+		return "", fe
+	}
+
+	return s, err
 }
 
 // The delta represents new output format-versions of the shortcodes,
@@ -417,7 +476,7 @@ func renderShortcode(
 // the content from the previous output format, if any.
 func (s *shortcodeHandler) updateDelta() bool {
 	s.init.Do(func() {
-		s.contentShortcodes = createShortcodeRenderers(s.shortcodes, s.p.withoutContent())
+		s.contentShortcodes = s.createShortcodeRenderers(s.p.withoutContent())
 	})
 
 	if !s.p.shouldRenderTo(s.p.s.rc.Format) {
@@ -505,13 +564,13 @@ func (s *shortcodeHandler) executeShortcodesForDelta(p *PageWithoutContent) erro
 
 }
 
-func createShortcodeRenderers(shortcodes *orderedMap, p *PageWithoutContent) *orderedMap {
+func (s *shortcodeHandler) createShortcodeRenderers(p *PageWithoutContent) *orderedMap {
 
 	shortcodeRenderers := newOrderedMap()
 
-	for _, k := range shortcodes.Keys() {
-		v := shortcodes.getShortcode(k)
-		prepared := prepareShortcodeForPage(k.(string), v, nil, p)
+	for _, k := range s.shortcodes.Keys() {
+		v := s.shortcodes.getShortcode(k)
+		prepared := s.prepareShortcodeForPage(k.(string), v, nil, p)
 		for kk, vv := range prepared {
 			shortcodeRenderers.Add(kk, vv)
 		}
@@ -541,7 +600,9 @@ Loop:
 		currItem := pt.Next()
 		switch {
 		case currItem.IsLeftShortcodeDelim():
-			sc.pos = currItem.Pos
+			if sc.pos == 0 {
+				sc.pos = currItem.Pos
+			}
 			next := pt.Peek()
 			if next.IsShortcodeClose() {
 				continue
@@ -570,13 +631,13 @@ Loop:
 		case currItem.IsRightShortcodeDelim():
 			// we trust the template on this:
 			// if there's no inner, we're done
-			if !isInner {
+			if !sc.isInline && !isInner {
 				return sc, nil
 			}
 
 		case currItem.IsShortcodeClose():
 			next := pt.Peek()
-			if !isInner {
+			if !sc.isInline && !isInner {
 				if next.IsError() {
 					// return that error, more specific
 					continue
@@ -588,6 +649,7 @@ Loop:
 				// self-closing
 				pt.Consume(1)
 			} else {
+				sc.isClosing = true
 				pt.Consume(2)
 			}
 
@@ -609,6 +671,10 @@ Loop:
 				return sc, fail(_errors.Wrapf(err, "failed to handle template for shortcode %q", sc.name), currItem)
 			}
 
+		case currItem.IsInlineShortcodeName():
+			sc.name = currItem.ValStr()
+			sc.isInline = true
+
 		case currItem.IsShortcodeParam():
 			if !pt.IsValueNext() {
 				continue
@@ -751,7 +817,7 @@ func renderShortcodeWithPage(tmpl tpl.Template, data *ShortcodeWithPage) (string
 	err := tmpl.Execute(buffer, data)
 	isInnerShortcodeCache.RUnlock()
 	if err != nil {
-		return "", data.Page.errorf(err, "failed to process shortcode")
+		return "", _errors.Wrap(err, "failed to process shortcode")
 	}
 	return buffer.String(), nil
 }