Split parse and render for Goldmark

This also speeds up situations where you only need the fragments/toc and not the rendered content, e.g. Related
with fragments type indexing:

```bash

name            old time/op    new time/op    delta
RelatedSite-10    12.3ms ± 2%    10.7ms ± 1%  -12.95%  (p=0.029 n=4+4)

name            old alloc/op   new alloc/op   delta
RelatedSite-10    38.6MB ± 0%    38.2MB ± 0%   -1.08%  (p=0.029 n=4+4)

name            old allocs/op  new allocs/op  delta
RelatedSite-10      117k ± 0%      115k ± 0%   -1.36%  (p=0.029 n=4+4)
```

Fixes #10750

7 files changed, 84 insertions, 26 deletions

diff --git a/markup/asciidocext/convert.go b/markup/asciidocext/convert.go
index c9524778f..c3bd90edd 100644
--- a/markup/asciidocext/convert.go
+++ b/markup/asciidocext/convert.go
@@ -52,7 +52,7 @@ func (p provider) New(cfg converter.ProviderConfig) (converter.Provider, error)
 }
 
 type asciidocResult struct {
-	converter.Result
+	converter.ResultRender
 	toc *tableofcontents.Fragments
 }
 
@@ -65,7 +65,7 @@ type asciidocConverter struct {
 	cfg converter.ProviderConfig
 }
 
-func (a *asciidocConverter) Convert(ctx converter.RenderContext) (converter.Result, error) {
+func (a *asciidocConverter) Convert(ctx converter.RenderContext) (converter.ResultRender, error) {
 	b, err := a.getAsciidocContent(ctx.Src, a.ctx)
 	if err != nil {
 		return nil, err
@@ -75,8 +75,8 @@ func (a *asciidocConverter) Convert(ctx converter.RenderContext) (converter.Resu
 		return nil, err
 	}
 	return asciidocResult{
-		Result: converter.Bytes(content),
-		toc:    toc,
+		ResultRender: converter.Bytes(content),
+		toc:          toc,
 	}, nil
 }
 
diff --git a/markup/converter/converter.go b/markup/converter/converter.go
index 7e5b56b07..e5a07f1a1 100644
--- a/markup/converter/converter.go
+++ b/markup/converter/converter.go
@@ -74,7 +74,7 @@ var NopConverter = new(nopConverter)
 
 type nopConverter int
 
-func (nopConverter) Convert(ctx RenderContext) (Result, error) {
+func (nopConverter) Convert(ctx RenderContext) (ResultRender, error) {
 	return &bytes.Buffer{}, nil
 }
 
@@ -85,15 +85,29 @@ func (nopConverter) Supports(feature identity.Identity) bool {
 // Converter wraps the Convert method that converts some markup into
 // another format, e.g. Markdown to HTML.
 type Converter interface {
-	Convert(ctx RenderContext) (Result, error)
+	Convert(ctx RenderContext) (ResultRender, error)
 	Supports(feature identity.Identity) bool
 }
 
-// Result represents the minimum returned from Convert.
-type Result interface {
+// ParseRenderer is an optional interface.
+// The Goldmark converter implements this, and this allows us
+// to extract the ToC without having to render the content.
+type ParseRenderer interface {
+	Parse(RenderContext) (ResultParse, error)
+	Render(RenderContext, any) (ResultRender, error)
+}
+
+// ResultRender represents the minimum returned from Convert and Render.
+type ResultRender interface {
 	Bytes() []byte
 }
 
+// ResultParse represents the minimum returned from Parse.
+type ResultParse interface {
+	Doc() any
+	TableOfContents() *tableofcontents.Fragments
+}
+
 // DocumentInfo holds additional information provided by some converters.
 type DocumentInfo interface {
 	AnchorSuffix() string
diff --git a/markup/goldmark/convert.go b/markup/goldmark/convert.go
index 6c1c7ad0a..3c8dbb299 100644
--- a/markup/goldmark/convert.go
+++ b/markup/goldmark/convert.go
@@ -18,6 +18,7 @@ import (
 	"bytes"
 
 	"github.com/gohugoio/hugo/identity"
+
 	"github.com/gohugoio/hugo/markup/goldmark/codeblocks"
 	"github.com/gohugoio/hugo/markup/goldmark/images"
 	"github.com/gohugoio/hugo/markup/goldmark/internal/extensions/attributes"
@@ -26,6 +27,7 @@ import (
 	"github.com/gohugoio/hugo/markup/converter"
 	"github.com/gohugoio/hugo/markup/tableofcontents"
 	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
 	"github.com/yuin/goldmark/extension"
 	"github.com/yuin/goldmark/parser"
 	"github.com/yuin/goldmark/renderer"
@@ -158,26 +160,41 @@ func newMarkdown(pcfg converter.ProviderConfig) goldmark.Markdown {
 
 var _ identity.IdentitiesProvider = (*converterResult)(nil)
 
-type converterResult struct {
-	converter.Result
+type parserResult struct {
+	doc any
 	toc *tableofcontents.Fragments
+}
+
+func (p parserResult) Doc() any {
+	return p.doc
+}
+
+func (p parserResult) TableOfContents() *tableofcontents.Fragments {
+	return p.toc
+}
+
+type renderResult struct {
+	converter.ResultRender
 	ids identity.Identities
 }
 
-func (c converterResult) TableOfContents() *tableofcontents.Fragments {
-	return c.toc
+func (r renderResult) GetIdentities() identity.Identities {
+	return r.ids
 }
 
-func (c converterResult) GetIdentities() identity.Identities {
-	return c.ids
+type converterResult struct {
+	converter.ResultRender
+	tableOfContentsProvider
+	identity.IdentitiesProvider
 }
 
-var converterIdentity = identity.KeyValueIdentity{Key: "goldmark", Value: "converter"}
+type tableOfContentsProvider interface {
+	TableOfContents() *tableofcontents.Fragments
+}
 
-func (c *goldmarkConverter) Convert(ctx converter.RenderContext) (result converter.Result, err error) {
+var converterIdentity = identity.KeyValueIdentity{Key: "goldmark", Value: "converter"}
 
-	buf := &render.BufWriter{Buffer: &bytes.Buffer{}}
-	result = buf
+func (c *goldmarkConverter) Parse(ctx converter.RenderContext) (converter.ResultParse, error) {
 	pctx := c.newParserContext(ctx)
 	reader := text.NewReader(ctx.Src)
 
@@ -186,6 +203,16 @@ func (c *goldmarkConverter) Convert(ctx converter.RenderContext) (result convert
 		parser.WithContext(pctx),
 	)
 
+	return parserResult{
+		doc: doc,
+		toc: pctx.TableOfContents(),
+	}, nil
+
+}
+func (c *goldmarkConverter) Render(ctx converter.RenderContext, doc any) (converter.ResultRender, error) {
+	n := doc.(ast.Node)
+	buf := &render.BufWriter{Buffer: &bytes.Buffer{}}
+
 	rcx := &render.RenderContextDataHolder{
 		Rctx: ctx,
 		Dctx: c.ctx,
@@ -197,15 +224,32 @@ func (c *goldmarkConverter) Convert(ctx converter.RenderContext) (result convert
 		ContextData: rcx,
 	}
 
-	if err := c.md.Renderer().Render(w, ctx.Src, doc); err != nil {
+	if err := c.md.Renderer().Render(w, ctx.Src, n); err != nil {
 		return nil, err
 	}
 
+	return renderResult{
+		ResultRender: buf,
+		ids:          rcx.IDs.GetIdentities(),
+	}, nil
+
+}
+
+func (c *goldmarkConverter) Convert(ctx converter.RenderContext) (converter.ResultRender, error) {
+	parseResult, err := c.Parse(ctx)
+	if err != nil {
+		return nil, err
+	}
+	renderResult, err := c.Render(ctx, parseResult.Doc())
+	if err != nil {
+		return nil, err
+	}
 	return converterResult{
-		Result: buf,
-		ids:    rcx.IDs.GetIdentities(),
-		toc:    pctx.TableOfContents(),
+		ResultRender:            renderResult,
+		tableOfContentsProvider: parseResult,
+		IdentitiesProvider:      renderResult.(identity.IdentitiesProvider),
 	}, nil
+
 }
 
 var featureSet = map[identity.Identity]bool{
diff --git a/markup/goldmark/convert_test.go b/markup/goldmark/convert_test.go
index cbc49d041..647ffce58 100644
--- a/markup/goldmark/convert_test.go
+++ b/markup/goldmark/convert_test.go
@@ -34,7 +34,7 @@ import (
 	qt "github.com/frankban/quicktest"
 )
 
-func convert(c *qt.C, mconf markup_config.Config, content string) converter.Result {
+func convert(c *qt.C, mconf markup_config.Config, content string) converter.ResultRender {
 	p, err := Provider.New(
 		converter.ProviderConfig{
 			MarkupConfig: mconf,
diff --git a/markup/org/convert.go b/markup/org/convert.go
index 603ec8f19..a08453e94 100644
--- a/markup/org/convert.go
+++ b/markup/org/convert.go
@@ -43,7 +43,7 @@ type orgConverter struct {
 	cfg converter.ProviderConfig
 }
 
-func (c *orgConverter) Convert(ctx converter.RenderContext) (converter.Result, error) {
+func (c *orgConverter) Convert(ctx converter.RenderContext) (converter.ResultRender, error) {
 	logger := c.cfg.Logger
 	config := org.New()
 	config.Log = logger.Warn()
diff --git a/markup/pandoc/convert.go b/markup/pandoc/convert.go
index ae90cf417..386a9ff26 100644
--- a/markup/pandoc/convert.go
+++ b/markup/pandoc/convert.go
@@ -43,7 +43,7 @@ type pandocConverter struct {
 	cfg converter.ProviderConfig
 }
 
-func (c *pandocConverter) Convert(ctx converter.RenderContext) (converter.Result, error) {
+func (c *pandocConverter) Convert(ctx converter.RenderContext) (converter.ResultRender, error) {
 	b, err := c.getPandocContent(ctx.Src, c.ctx)
 	if err != nil {
 		return nil, err
diff --git a/markup/rst/convert.go b/markup/rst/convert.go
index b86b35f1b..59ce38408 100644
--- a/markup/rst/convert.go
+++ b/markup/rst/convert.go
@@ -47,7 +47,7 @@ type rstConverter struct {
 	cfg converter.ProviderConfig
 }
 
-func (c *rstConverter) Convert(ctx converter.RenderContext) (converter.Result, error) {
+func (c *rstConverter) Convert(ctx converter.RenderContext) (converter.ResultRender, error) {
 	b, err := c.getRstContent(ctx.Src, c.ctx)
 	if err != nil {
 		return nil, err