Fix markup heading parsing, fix emphasis parsing (#36284)

Fixes #36106, fix #17958

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/markup/html.go

@@ -12,7 +12,9 @@ import (
 	"strings"
 	"sync"
 
+	"code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/markup/common"
+	"code.gitea.io/gitea/modules/translation"
 
 	"golang.org/x/net/html"
 	"golang.org/x/net/html/atom"
@@ -234,6 +236,49 @@ func postProcessString(ctx *RenderContext, procs []processor, content string) (s
 	return buf.String(), nil
 }
 
+func RenderTocHeadingItems(ctx *RenderContext, nodeDetailsAttrs map[string]string, out io.Writer) {
+	locale, ok := ctx.Value(translation.ContextKey).(translation.Locale)
+	if !ok {
+		locale = translation.NewLocale("")
+	}
+	_, _ = htmlutil.HTMLPrintTag(out, "details", nodeDetailsAttrs)
+	_, _ = htmlutil.HTMLPrintf(out, "<summary>%s</summary>\n", locale.TrString("toc"))
+
+	baseLevel := 6
+	for _, header := range ctx.TocHeadingItems {
+		if header.HeadingLevel < baseLevel {
+			baseLevel = header.HeadingLevel
+		}
+	}
+
+	currentLevel := baseLevel
+	indent := []byte{' ', ' '}
+	_, _ = htmlutil.HTMLPrint(out, "<ul>\n")
+	for _, header := range ctx.TocHeadingItems {
+		for currentLevel < header.HeadingLevel {
+			_, _ = out.Write(indent)
+			_, _ = htmlutil.HTMLPrint(out, "<ul>\n")
+			indent = append(indent, ' ', ' ')
+			currentLevel++
+		}
+		for currentLevel > header.HeadingLevel {
+			indent = indent[:len(indent)-2]
+			_, _ = out.Write(indent)
+			_, _ = htmlutil.HTMLPrint(out, "</ul>\n")
+			currentLevel--
+		}
+		_, _ = out.Write(indent)
+		_, _ = htmlutil.HTMLPrintf(out, "<li><a href=\"#%s\">%s</a></li>\n", header.AnchorID, header.InnerText)
+	}
+	for currentLevel > baseLevel {
+		indent = indent[:len(indent)-2]
+		_, _ = out.Write(indent)
+		_, _ = htmlutil.HTMLPrint(out, "</ul>\n")
+		currentLevel--
+	}
+	_, _ = htmlutil.HTMLPrint(out, "</ul>\n</details>\n")
+}
+
 func postProcess(ctx *RenderContext, procs []processor, input io.Reader, output io.Writer) error {
 	if !ctx.usedByRender && ctx.RenderHelper != nil {
 		defer ctx.RenderHelper.CleanUp()
@@ -284,6 +329,9 @@ func postProcess(ctx *RenderContext, procs []processor, input io.Reader, output
 	}
 
 	// Render everything to buf.
+	if ctx.TocShowInSection == TocShowInMain && len(ctx.TocHeadingItems) > 0 {
+		RenderTocHeadingItems(ctx, nil, output)
+	}
 	for _, node := range newNodes {
 		if err := html.Render(output, node); err != nil {
 			return fmt.Errorf("markup.postProcess: html.Render: %w", err)
@@ -314,7 +362,7 @@ func visitNode(ctx *RenderContext, procs []processor, node *html.Node) *html.Nod
 		return node.NextSibling
 	}
 
-	processNodeAttrID(ctx, node)
+	processNodeHeadingAndID(ctx, node)
 	processFootnoteNode(ctx, node) // FIXME: the footnote processing should be done in the "footnote.go" renderer directly
 
 	if isEmojiNode(node) {