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, 3 insertions, 2 deletions

diff --git a/markup/converter/hooks/hooks.go b/markup/converter/hooks/hooks.go
index 54ebf405e..2f2d5e6cb 100644
--- a/markup/converter/hooks/hooks.go
+++ b/markup/converter/hooks/hooks.go
@@ -18,6 +18,7 @@ import (
 
 	"github.com/gohugoio/hugo/common/hugio"
 	"github.com/gohugoio/hugo/common/text"
+	"github.com/gohugoio/hugo/common/types/hstring"
 	"github.com/gohugoio/hugo/identity"
 	"github.com/gohugoio/hugo/markup/internal/attributes"
 )
@@ -32,7 +33,7 @@ type LinkContext interface {
 	Page() interface{}
 	Destination() string
 	Title() string
-	Text() string
+	Text() hstring.RenderedString
 	PlainText() string
 }
 
@@ -75,7 +76,7 @@ type HeadingContext interface {
 	// Anchor is the HTML id assigned to the heading.
 	Anchor() string
 	// Text is the rendered (HTML) heading text, excluding the heading marker.
-	Text() string
+	Text() hstring.RenderedString
 	// PlainText is the unrendered version of Text.
 	PlainText() string