Add "target" and "rel" parameters to figure shortcode

Also:

- Remove unnecessary space from `figure` tag if no class is specified.
  - Update related tests.
- Add test cases for the changes made to the figure shortcode.
- Document the newly added target and rel parameters
- Add more detail to the documentation of all figure shortcode parameters.

docs/content/content-management/shortcodes.md

@@ -80,15 +80,41 @@ Hugo ships with a set of predefined shortcodes that represent very common usage.
 
 The `figure` shortcode can use the following named parameters:
 
-* `src`
-* `link`
-* `title`
-* `caption`
-* `class`
-* `attr` (i.e., attribution)
-* `attrlink`
-* `alt`
-* `width`
+src
+: URL of the image to be displayed.
+
+link
+: If the image needs to be hyperlinked, URL of the destination.
+
+target
+: Optional `target` attribute for the URL if `link` parameter is set.
+
+rel
+: Optional `rel` attribute for the URL if `link` parameter is set.
+
+alt
+: Alternate text for the image if the image cannot be displayed.
+
+title
+: Image title.
+
+caption
+: Image caption.
+
+class
+: `class` attribute of the HTML `figure` tag.
+
+height
+: `height` attribute of the image.
+
+width
+: `width` attribute of the image.
+
+attr
+: Image attribution text.
+
+attrlink
+: If the attribution text needs to be hyperlinked, URL of the destination.
 
 #### Example `figure` Input
 

hugolib/shortcode_test.go

@@ -293,6 +293,11 @@ func TestParentShortcode(t *testing.T) {
 
 }
 
+func TestFigureOnlySrc(t *testing.T) {
+	t.Parallel()
+	CheckShortCodeMatch(t, `{{< figure src="/found/here" >}}`, "\n<figure>\n    \n        <img src=\"/found/here\" />\n    \n    \n</figure>\n", nil)
+}
+
 func TestFigureImgWidth(t *testing.T) {
 	t.Parallel()
 	CheckShortCodeMatch(t, `{{% figure src="/found/here" class="bananas orange" alt="apple" width="100px" %}}`, "\n<figure class=\"bananas orange\">\n    \n        <img src=\"/found/here\" alt=\"apple\" width=\"100px\" />\n    \n    \n</figure>\n", nil)
@@ -308,6 +313,21 @@ func TestFigureImgWidthAndHeight(t *testing.T) {
 	CheckShortCodeMatch(t, `{{% figure src="/found/here" class="bananas orange" alt="apple" width="50" height="100" %}}`, "\n<figure class=\"bananas orange\">\n    \n        <img src=\"/found/here\" alt=\"apple\" width=\"50\" height=\"100\" />\n    \n    \n</figure>\n", nil)
 }
 
+func TestFigureLinkNoTarget(t *testing.T) {
+	t.Parallel()
+	CheckShortCodeMatch(t, `{{< figure src="/found/here" link="/jump/here/on/clicking" >}}`, "\n<figure>\n    <a href=\"/jump/here/on/clicking\">\n        <img src=\"/found/here\" />\n    </a>\n    \n</figure>\n", nil)
+}
+
+func TestFigureLinkWithTarget(t *testing.T) {
+	t.Parallel()
+	CheckShortCodeMatch(t, `{{< figure src="/found/here" link="/jump/here/on/clicking" target="_self" >}}`, "\n<figure>\n    <a href=\"/jump/here/on/clicking\" target=\"_self\">\n        <img src=\"/found/here\" />\n    </a>\n    \n</figure>\n", nil)
+}
+
+func TestFigureLinkWithTargetAndRel(t *testing.T) {
+	t.Parallel()
+	CheckShortCodeMatch(t, `{{< figure src="/found/here" link="/jump/here/on/clicking" target="_blank" rel="noopener" >}}`, "\n<figure>\n    <a href=\"/jump/here/on/clicking\" target=\"_blank\" rel=\"noopener\">\n        <img src=\"/found/here\" />\n    </a>\n    \n</figure>\n", nil)
+}
+
 const testScPlaceholderRegexp = "HAHAHUGOSHORTCODE-\\d+HBHB"
 
 func TestExtractShortcodes(t *testing.T) {

tpl/tplimpl/template_embedded.go

@@ -20,7 +20,7 @@ func (t *templateHandler) embedShortcodes() {
 	t.addInternalShortcode("test.html", `This is a simple Test`)
 	t.addInternalShortcode("figure.html", `<!-- image -->
 <figure{{ with .Get "class" }} class="{{.}}"{{ end }}>
-    {{ with .Get "link"}}<a href="{{.}}">{{ end }}
+    {{ if .Get "link"}}<a href="{{ .Get "link" }}"{{ with .Get "target" }} target="{{ . }}"{{ end }}{{ with .Get "rel" }} rel="{{ . }}"{{ end }}>{{ end }}
         <img src="{{ .Get "src" }}" {{ if or (.Get "alt") (.Get "caption") }}alt="{{ with .Get "alt"}}{{.}}{{else}}{{ .Get "caption" }}{{ end }}" {{ end }}{{ with .Get "width" }}width="{{.}}" {{ end }}{{ with .Get "height" }}height="{{.}}" {{ end }}/>
     {{ if .Get "link"}}</a>{{ end }}
     {{ if or (or (.Get "title") (.Get "caption")) (.Get "attr")}}