Fail with error when double-rendering text in markdownify/RenderString

This commit prevents the most commons case of infinite recursion in link render hooks when the `linkify` option is enabled (see below). This is always a user error, but getting a `stack overflow` (the current stack limit in Go is 1 GB on 64-bit, 250 MB on 32-bit) error isn't very helpful. This fix will not prevent all such errors, though, but we may do better once #9570 is in place.

So, these will fail:

```
<a href="{{ .Destination | safeURL }}" >{{ .Text | markdownify }}</a>
<a href="{{ .Destination | safeURL }}" >{{ .Text | .Page.RenderString }}</a>
```

`.Text` is already rendered to `HTML`. The above needs to be rewritten to:

```
<a href="{{ .Destination | safeURL }}" >{{ .Text | safeHTML }}</a>
<a href="{{ .Destination | safeURL }}" >{{ .Text | safeHTML }}</a>
```

Fixes #8959

1 files changed, 5 insertions, 8 deletions

diff --git a/tpl/transform/transform.go b/tpl/transform/transform.go
index 48cfaffff..498c0d674 100644
--- a/tpl/transform/transform.go
+++ b/tpl/transform/transform.go
@@ -20,7 +20,6 @@ import (
 
 	"github.com/alecthomas/chroma/lexers"
 	"github.com/gohugoio/hugo/cache/namedmemcache"
-	"github.com/gohugoio/hugo/common/herrors"
 	"github.com/gohugoio/hugo/markup/converter/hooks"
 	"github.com/gohugoio/hugo/markup/highlight"
 
@@ -119,20 +118,18 @@ func (ns *Namespace) HTMLUnescape(s interface{}) (string, error) {
 
 // Markdownify renders a given input from Markdown to HTML.
 func (ns *Namespace) Markdownify(s interface{}) (template.HTML, error) {
-	defer herrors.Recover()
-	ss, err := cast.ToStringE(s)
-	if err != nil {
-		return "", err
-	}
 
 	home := ns.deps.Site.Home()
 	if home == nil {
 		panic("home must not be nil")
 	}
-	sss, err := home.RenderString(ss)
+	ss, err := home.RenderString(s)
+	if err != nil {
+		return "", err
+	}
 
 	// Strip if this is a short inline type of text.
-	bb := ns.deps.ContentSpec.TrimShortHTML([]byte(sss))
+	bb := ns.deps.ContentSpec.TrimShortHTML([]byte(ss))
 
 	return helpers.BytesToHTML(bb), nil
 }