Add KaTeX rendering to Markdown. (#20571)

This PR adds mathematical rendering with KaTeX.

The first step is to add a Goldmark extension that detects the latex
(and tex) mathematics delimiters.

The second step to make this extension only run if math support is
enabled.

The second step is to then add KaTeX CSS and JS to the head which will
load after the dom is rendered.

Fix #3445

Signed-off-by: Andrew Thornton <art27@cantab.net>

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

custom/conf/app.example.ini

@@ -1262,6 +1262,9 @@ ROUTER = console
 ;; List of file extensions that should be rendered/edited as Markdown
 ;; Separate the extensions with a comma. To render files without any extension as markdown, just put a comma
 ;FILE_EXTENSIONS = .md,.markdown,.mdown,.mkd
+;;
+;; Enables math inline and block detection
+;ENABLE_MATH = true
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -236,6 +236,7 @@ The following configuration set `Content-Type: application/vnd.android.package-a
 - `CUSTOM_URL_SCHEMES`: Use a comma separated list (ftp,git,svn) to indicate additional
   URL hyperlinks to be rendered in Markdown. URLs beginning in http and https are
   always displayed
+- `ENABLE_MATH`: **true**: Enables detection of `\(...\)`, `\[...\]`, `$...$` and `$$...$$` blocks as math blocks.
 
 ## Server (`server`)
 

docs/content/doc/advanced/external-renderers.en-us.md

@@ -74,12 +74,13 @@ RENDER_COMMAND = "timeout 30s pandoc +RTS -M512M -RTS -f rst"
 IS_INPUT_FILE = false
 ```
 
-If your external markup relies on additional classes and attributes on the generated HTML elements, you might need to enable custom sanitizer policies. Gitea uses the [`bluemonday`](https://godoc.org/github.com/microcosm-cc/bluemonday) package as our HTML sanitizier. The example below will support [KaTeX](https://katex.org/) output from [`pandoc`](https://pandoc.org/).
+If your external markup relies on additional classes and attributes on the generated HTML elements, you might need to enable custom sanitizer policies. Gitea uses the [`bluemonday`](https://godoc.org/github.com/microcosm-cc/bluemonday) package as our HTML sanitizer. The example below could be used to support server-side [KaTeX](https://katex.org/) rendering output from [`pandoc`](https://pandoc.org/).
 
 ```ini
 [markup.sanitizer.TeX]
 ; Pandoc renders TeX segments as <span>s with the "math" class, optionally
 ; with "inline" or "display" classes depending on context.
+; - note this is different from the built-in math support in our markdown parser which uses <code>
 ELEMENT = span
 ALLOW_ATTR = class
 REGEXP = ^\s*((math(\s+|$)|inline(\s+|$)|display(\s+|$)))+

docs/content/doc/features/comparison.en-us.md

@@ -53,6 +53,8 @@ _Symbols used in table:_
 | WebAuthn (2FA)                      | ✓                                                  | ✘    | ✓         | ✓         | ✓         | ✓              | ?            |
 | Built-in CI/CD                      | ✘                                                  | ✘    | ✓         | ✓         | ✓         | ✘              | ✘            |
 | Subgroups: groups within groups     | [✘](https://github.com/go-gitea/gitea/issues/1872) | ✘    | ✘         | ✓         | ✓         | ✘              | ✓            |
+| Mermaid diagrams in Markdown        | ✓                                                  | ✘    | ✓         | ✓         | ✓         | ✘              | ✘            |
+| Math syntax in Markdown             | ✓                                                  | ✘    | ✓         | ✓         | ✓         | ✘              | ✘            |
 
 ## Code management
 

docs/content/page/index.en-us.md

@@ -131,7 +131,8 @@ You can try it out using [the online demo](https://try.gitea.io/).
   - Environment variables
   - Command line options
 - Multi-language support ([21 languages](https://github.com/go-gitea/gitea/tree/main/options/locale))
-- [Mermaid](https://mermaidjs.github.io/) Diagram support
+- [Mermaid](https://mermaidjs.github.io/) diagrams in Markdown
+- Math syntax in Markdown
 - Mail service
   - Notifications
   - Registration confirmation

go.mod

@@ -103,6 +103,7 @@ require (
 	gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df
 	gopkg.in/ini.v1 v1.67.0
 	gopkg.in/yaml.v2 v2.4.0
+	gopkg.in/yaml.v3 v3.0.1
 	mvdan.cc/xurls/v2 v2.4.0
 	strk.kbt.io/projects/go/libravatar v0.0.0-20191008002943-06d1c002b251
 	xorm.io/builder v0.3.11
@@ -290,7 +291,6 @@ require (
 	gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc // indirect
 	gopkg.in/cheggaaa/pb.v1 v1.0.28 // indirect
 	gopkg.in/warnings.v0 v0.1.2 // indirect
-	gopkg.in/yaml.v3 v3.0.1 // indirect
 	sigs.k8s.io/yaml v1.2.0 // indirect
 )
 

modules/markup/markdown/convertyaml.go

@@ -0,0 +1,84 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package markdown
+
+import (
+	"github.com/yuin/goldmark/ast"
+	east "github.com/yuin/goldmark/extension/ast"
+	"gopkg.in/yaml.v3"
+)
+
+func nodeToTable(meta *yaml.Node) ast.Node {
+	for {
+		if meta == nil {
+			return nil
+		}
+		switch meta.Kind {
+		case yaml.DocumentNode:
+			meta = meta.Content[0]
+			continue
+		default:
+		}
+		break
+	}
+	switch meta.Kind {
+	case yaml.MappingNode:
+		return mappingNodeToTable(meta)
+	case yaml.SequenceNode:
+		return sequenceNodeToTable(meta)
+	default:
+		return ast.NewString([]byte(meta.Value))
+	}
+}
+
+func mappingNodeToTable(meta *yaml.Node) ast.Node {
+	table := east.NewTable()
+	alignments := []east.Alignment{}
+	for i := 0; i < len(meta.Content); i += 2 {
+		alignments = append(alignments, east.AlignNone)
+	}
+
+	headerRow := east.NewTableRow(alignments)
+	valueRow := east.NewTableRow(alignments)
+	for i := 0; i < len(meta.Content); i += 2 {
+		cell := east.NewTableCell()
+
+		cell.AppendChild(cell, nodeToTable(meta.Content[i]))
+		headerRow.AppendChild(headerRow, cell)
+
+		if i+1 < len(meta.Content) {
+			cell = east.NewTableCell()
+			cell.AppendChild(cell, nodeToTable(meta.Content[i+1]))
+			valueRow.AppendChild(valueRow, cell)
+		}
+	}
+
+	table.AppendChild(table, east.NewTableHeader(headerRow))
+	table.AppendChild(table, valueRow)
+	return table
+}
+
+func sequenceNodeToTable(meta *yaml.Node) ast.Node {
+	table := east.NewTable()
+	alignments := []east.Alignment{east.AlignNone}
+	for _, item := range meta.Content {
+		row := east.NewTableRow(alignments)
+		cell := east.NewTableCell()
+		cell.AppendChild(cell, nodeToTable(item))
+		row.AppendChild(row, cell)
+		table.AppendChild(table, row)
+	}
+	return table
+}
+
+func nodeToDetails(meta *yaml.Node, icon string) ast.Node {
+	details := NewDetails()
+	summary := NewSummary()
+	summary.AppendChild(summary, NewIcon(icon))
+	details.AppendChild(details, summary)
+	details.AppendChild(details, nodeToTable(meta))
+
+	return details
+}

modules/markup/markdown/goldmark.go

@@ -15,7 +15,6 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	giteautil "code.gitea.io/gitea/modules/util"
 
-	meta "github.com/yuin/goldmark-meta"
 	"github.com/yuin/goldmark/ast"
 	east "github.com/yuin/goldmark/extension/ast"
 	"github.com/yuin/goldmark/parser"
@@ -32,20 +31,12 @@ type ASTTransformer struct{}
 
 // Transform transforms the given AST tree.
 func (g *ASTTransformer) Transform(node *ast.Document, reader text.Reader, pc parser.Context) {
-	metaData := meta.GetItems(pc)
 	firstChild := node.FirstChild()
 	createTOC := false
 	ctx := pc.Get(renderContextKey).(*markup.RenderContext)
-	rc := &RenderConfig{
-		Meta: "table",
-		Icon: "table",
-		Lang: "",
-	}
-
-	if metaData != nil {
-		rc.ToRenderConfig(metaData)
-
-		metaNode := rc.toMetaNode(metaData)
+	rc := pc.Get(renderConfigKey).(*RenderConfig)
+	if rc.yamlNode != nil {
+		metaNode := rc.toMetaNode()
 		if metaNode != nil {
 			node.InsertBefore(node, firstChild, metaNode)
 		}

modules/markup/markdown/markdown.go

@@ -14,6 +14,7 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/markup/common"
+	"code.gitea.io/gitea/modules/markup/markdown/math"
 	"code.gitea.io/gitea/modules/setting"
 	giteautil "code.gitea.io/gitea/modules/util"
 
@@ -38,6 +39,7 @@ var (
 	isWikiKey        = parser.NewContextKey()
 	renderMetasKey   = parser.NewContextKey()
 	renderContextKey = parser.NewContextKey()
+	renderConfigKey  = parser.NewContextKey()
 )
 
 type limitWriter struct {
@@ -98,7 +100,7 @@ func actualRender(ctx *markup.RenderContext, input io.Reader, output io.Writer)
 							languageStr := string(language)
 
 							preClasses := []string{"code-block"}
-							if languageStr == "mermaid" {
+							if languageStr == "mermaid" || languageStr == "math" {
 								preClasses = append(preClasses, "is-loading")
 							}
 
@@ -120,6 +122,9 @@ func actualRender(ctx *markup.RenderContext, input io.Reader, output io.Writer)
 						}
 					}),
 				),
+				math.NewExtension(
+					math.Enabled(setting.Markdown.EnableMath),
+				),
 				meta.Meta,
 			),
 			goldmark.WithParserOptions(
@@ -167,7 +172,18 @@ func actualRender(ctx *markup.RenderContext, input io.Reader, output io.Writer)
 		log.Error("Unable to ReadAll: %v", err)
 		return err
 	}
-	if err := converter.Convert(giteautil.NormalizeEOL(buf), lw, parser.WithContext(pc)); err != nil {
+	buf = giteautil.NormalizeEOL(buf)
+
+	rc := &RenderConfig{
+		Meta: "table",
+		Icon: "table",
+		Lang: "",
+	}
+	buf, _ = ExtractMetadataBytes(buf, rc)
+
+	pc.Set(renderConfigKey, rc)
+
+	if err := converter.Convert(buf, lw, parser.WithContext(pc)); err != nil {
 		log.Error("Unable to render: %v", err)
 		return err
 	}

modules/markup/markdown/math/block_node.go

@@ -0,0 +1,42 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package math
+
+import "github.com/yuin/goldmark/ast"
+
+// Block represents a display math block e.g. $$...$$ or \[...\]
+type Block struct {
+	ast.BaseBlock
+	Dollars bool
+	Indent  int
+	Closed  bool
+}
+
+// KindBlock is the node kind for math blocks
+var KindBlock = ast.NewNodeKind("MathBlock")
+
+// NewBlock creates a new math Block
+func NewBlock(dollars bool, indent int) *Block {
+	return &Block{
+		Dollars: dollars,
+		Indent:  indent,
+	}
+}
+
+// Dump dumps the block to a string
+func (n *Block) Dump(source []byte, level int) {
+	m := map[string]string{}
+	ast.DumpHelper(n, source, level, m, nil)
+}
+
+// Kind returns KindBlock for math Blocks
+func (n *Block) Kind() ast.NodeKind {
+	return KindBlock
+}
+
+// IsRaw returns true as this block should not be processed further
+func (n *Block) IsRaw() bool {
+	return true
+}

modules/markup/markdown/math/block_parser.go

@@ -0,0 +1,123 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package math
+
+import (
+	"bytes"
+
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+)
+
+type blockParser struct {
+	parseDollars bool
+}
+
+// NewBlockParser creates a new math BlockParser
+func NewBlockParser(parseDollarBlocks bool) parser.BlockParser {
+	return &blockParser{
+		parseDollars: parseDollarBlocks,
+	}
+}
+
+// Open parses the current line and returns a result of parsing.
+func (b *blockParser) Open(parent ast.Node, reader text.Reader, pc parser.Context) (ast.Node, parser.State) {
+	line, segment := reader.PeekLine()
+	pos := pc.BlockOffset()
+	if pos == -1 || len(line[pos:]) < 2 {
+		return nil, parser.NoChildren
+	}
+
+	dollars := false
+	if b.parseDollars && line[pos] == '$' && line[pos+1] == '$' {
+		dollars = true
+	} else if line[pos] != '\\' || line[pos+1] != '[' {
+		return nil, parser.NoChildren
+	}
+
+	node := NewBlock(dollars, pos)
+
+	// Now we need to check if the ending block is on the segment...
+	endBytes := []byte{'\\', ']'}
+	if dollars {
+		endBytes = []byte{'$', '$'}
+	}
+	idx := bytes.Index(line[pos+2:], endBytes)
+	if idx >= 0 {
+		segment.Stop = segment.Start + idx + 2
+		reader.Advance(segment.Len() - 1)
+		segment.Start += 2
+		node.Lines().Append(segment)
+		node.Closed = true
+		return node, parser.Close | parser.NoChildren
+	}
+
+	reader.Advance(segment.Len() - 1)
+	segment.Start += 2
+	node.Lines().Append(segment)
+	return node, parser.NoChildren
+}
+
+// Continue parses the current line and returns a result of parsing.
+func (b *blockParser) Continue(node ast.Node, reader text.Reader, pc parser.Context) parser.State {
+	block := node.(*Block)
+	if block.Closed {
+		return parser.Close
+	}
+
+	line, segment := reader.PeekLine()
+	w, pos := util.IndentWidth(line, 0)
+	if w < 4 {
+		if block.Dollars {
+			i := pos
+			for ; i < len(line) && line[i] == '$'; i++ {
+			}
+			length := i - pos
+			if length >= 2 && util.IsBlank(line[i:]) {
+				reader.Advance(segment.Stop - segment.Start - segment.Padding)
+				block.Closed = true
+				return parser.Close
+			}
+		} else if len(line[pos:]) > 1 && line[pos] == '\\' && line[pos+1] == ']' && util.IsBlank(line[pos+2:]) {
+			reader.Advance(segment.Stop - segment.Start - segment.Padding)
+			block.Closed = true
+			return parser.Close
+		}
+	}
+
+	pos, padding := util.IndentPosition(line, 0, block.Indent)
+	seg := text.NewSegmentPadding(segment.Start+pos, segment.Stop, padding)
+	node.Lines().Append(seg)
+	reader.AdvanceAndSetPadding(segment.Stop-segment.Start-pos-1, padding)
+	return parser.Continue | parser.NoChildren
+}
+
+// Close will be called when the parser returns Close.
+func (b *blockParser) Close(node ast.Node, reader text.Reader, pc parser.Context) {
+	// noop
+}
+
+// CanInterruptParagraph returns true if the parser can interrupt paragraphs,
+// otherwise false.
+func (b *blockParser) CanInterruptParagraph() bool {
+	return true
+}
+
+// CanAcceptIndentedLine returns true if the parser can open new node when
+// the given line is being indented more than 3 spaces.
+func (b *blockParser) CanAcceptIndentedLine() bool {
+	return false
+}
+
+// Trigger returns a list of characters that triggers Parse method of
+// this parser.
+// If Trigger returns a nil, Open will be called with any lines.
+//
+// We leave this as nil as our parse method is quick enough
+func (b *blockParser) Trigger() []byte {
+	return nil
+}

modules/markup/markdown/math/block_renderer.go

@@ -0,0 +1,43 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package math
+
+import (
+	gast "github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/renderer"
+	"github.com/yuin/goldmark/util"
+)
+
+// BlockRenderer represents a renderer for math Blocks
+type BlockRenderer struct{}
+
+// NewBlockRenderer creates a new renderer for math Blocks
+func NewBlockRenderer() renderer.NodeRenderer {
+	return &BlockRenderer{}
+}
+
+// RegisterFuncs registers the renderer for math Blocks
+func (r *BlockRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	reg.Register(KindBlock, r.renderBlock)
+}
+
+func (r *BlockRenderer) writeLines(w util.BufWriter, source []byte, n gast.Node) {
+	l := n.Lines().Len()
+	for i := 0; i < l; i++ {
+		line := n.Lines().At(i)
+		_, _ = w.Write(util.EscapeHTML(line.Value(source)))
+	}
+}
+
+func (r *BlockRenderer) renderBlock(w util.BufWriter, source []byte, node gast.Node, entering bool) (gast.WalkStatus, error) {
+	n := node.(*Block)
+	if entering {
+		_, _ = w.WriteString(`<pre class="code-block is-loading"><code class="chroma language-math display">`)
+		r.writeLines(w, source, n)
+	} else {
+		_, _ = w.WriteString(`</code></pre>` + "\n")
+	}
+	return gast.WalkContinue, nil
+}

modules/markup/markdown/math/inline_node.go

@@ -0,0 +1,49 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package math
+
+import (
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/util"
+)
+
+// Inline represents inline math e.g. $...$ or \(...\)
+type Inline struct {
+	ast.BaseInline
+}
+
+// Inline implements Inline.Inline.
+func (n *Inline) Inline() {}
+
+// IsBlank returns if this inline node is empty
+func (n *Inline) IsBlank(source []byte) bool {
+	for c := n.FirstChild(); c != nil; c = c.NextSibling() {
+		text := c.(*ast.Text).Segment
+		if !util.IsBlank(text.Value(source)) {
+			return false
+		}
+	}
+	return true
+}
+
+// Dump renders this inline math as debug
+func (n *Inline) Dump(source []byte, level int) {
+	ast.DumpHelper(n, source, level, nil, nil)
+}
+
+// KindInline is the kind for math inline
+var KindInline = ast.NewNodeKind("MathInline")
+
+// Kind returns KindInline
+func (n *Inline) Kind() ast.NodeKind {
+	return KindInline
+}
+
+// NewInline creates a new ast math inline node
+func NewInline() *Inline {
+	return &Inline{
+		BaseInline: ast.BaseInline{},
+	}
+}

modules/markup/markdown/math/inline_parser.go

@@ -0,0 +1,99 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package math
+
+import (
+	"bytes"
+
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+)
+
+type inlineParser struct {
+	start []byte
+	end   []byte
+}
+
+var defaultInlineDollarParser = &inlineParser{
+	start: []byte{'$'},
+	end:   []byte{'$'},
+}
+
+// NewInlineDollarParser returns a new inline parser
+func NewInlineDollarParser() parser.InlineParser {
+	return defaultInlineDollarParser
+}
+
+var defaultInlineBracketParser = &inlineParser{
+	start: []byte{'\\', '('},
+	end:   []byte{'\\', ')'},
+}
+
+// NewInlineDollarParser returns a new inline parser
+func NewInlineBracketParser() parser.InlineParser {
+	return defaultInlineBracketParser
+}
+
+// Trigger triggers this parser on $
+func (parser *inlineParser) Trigger() []byte {
+	return parser.start[0:1]
+}
+
+func isAlphanumeric(b byte) bool {
+	// Github only cares about 0-9A-Za-z
+	return (b >= '0' && b <= '9') || (b >= 'A' && b <= 'Z') || (b >= 'a' && b <= 'z')
+}
+
+// Parse parses the current line and returns a result of parsing.
+func (parser *inlineParser) Parse(parent ast.Node, block text.Reader, pc parser.Context) ast.Node {
+	line, _ := block.PeekLine()
+	opener := bytes.Index(line, parser.start)
+	if opener < 0 {
+		return nil
+	}
+	if opener != 0 && isAlphanumeric(line[opener-1]) {
+		return nil
+	}
+
+	opener += len(parser.start)
+	ender := bytes.Index(line[opener:], parser.end)
+	if ender < 0 {
+		return nil
+	}
+	if len(line) > opener+ender+len(parser.end) && isAlphanumeric(line[opener+ender+len(parser.end)]) {
+		return nil
+	}
+
+	block.Advance(opener)
+	_, pos := block.Position()
+	node := NewInline()
+	segment := pos.WithStop(pos.Start + ender)
+	node.AppendChild(node, ast.NewRawTextSegment(segment))
+	block.Advance(ender + len(parser.end))
+
+	trimBlock(node, block)
+	return node
+}
+
+func trimBlock(node *Inline, block text.Reader) {
+	if node.IsBlank(block.Source()) {
+		return
+	}
+
+	// trim first space and last space
+	first := node.FirstChild().(*ast.Text)
+	if !(!first.Segment.IsEmpty() && block.Source()[first.Segment.Start] == ' ') {
+		return
+	}
+
+	last := node.LastChild().(*ast.Text)
+	if !(!last.Segment.IsEmpty() && block.Source()[last.Segment.Stop-1] == ' ') {
+		return
+	}
+
+	first.Segment = first.Segment.WithStart(first.Segment.Start + 1)
+	last.Segment = last.Segment.WithStop(last.Segment.Stop - 1)
+}

modules/markup/markdown/math/inline_renderer.go

@@ -0,0 +1,47 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package math
+
+import (
+	"bytes"
+
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/renderer"
+	"github.com/yuin/goldmark/util"
+)
+
+// InlineRenderer is an inline renderer
+type InlineRenderer struct{}
+
+// NewInlineRenderer returns a new renderer for inline math
+func NewInlineRenderer() renderer.NodeRenderer {
+	return &InlineRenderer{}
+}
+
+func (r *InlineRenderer) renderInline(w util.BufWriter, source []byte, n ast.Node, entering bool) (ast.WalkStatus, error) {
+	if entering {
+		_, _ = w.WriteString(`<code class="language-math is-loading">`)
+		for c := n.FirstChild(); c != nil; c = c.NextSibling() {
+			segment := c.(*ast.Text).Segment
+			value := util.EscapeHTML(segment.Value(source))
+			if bytes.HasSuffix(value, []byte("\n")) {
+				_, _ = w.Write(value[:len(value)-1])
+				if c != n.LastChild() {
+					_, _ = w.Write([]byte(" "))
+				}
+			} else {
+				_, _ = w.Write(value)
+			}
+		}
+		return ast.WalkSkipChildren, nil
+	}
+	_, _ = w.WriteString(`</code>`)
+	return ast.WalkContinue, nil
+}
+
+// RegisterFuncs registers the renderer for inline math nodes
+func (r *InlineRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	reg.Register(KindInline, r.renderInline)
+}

modules/markup/markdown/math/math.go

@@ -0,0 +1,108 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package math
+
+import (
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/renderer"
+	"github.com/yuin/goldmark/util"
+)
+
+// Extension is a math extension
+type Extension struct {
+	enabled           bool
+	parseDollarInline bool
+	parseDollarBlock  bool
+}
+
+// Option is the interface Options should implement
+type Option interface {
+	SetOption(e *Extension)
+}
+
+type extensionFunc func(e *Extension)
+
+func (fn extensionFunc) SetOption(e *Extension) {
+	fn(e)
+}
+
+// Enabled enables or disables this extension
+func Enabled(enable ...bool) Option {
+	value := true
+	if len(enable) > 0 {
+		value = enable[0]
+	}
+	return extensionFunc(func(e *Extension) {
+		e.enabled = value
+	})
+}
+
+// WithInlineDollarParser enables or disables the parsing of $...$
+func WithInlineDollarParser(enable ...bool) Option {
+	value := true
+	if len(enable) > 0 {
+		value = enable[0]
+	}
+	return extensionFunc(func(e *Extension) {
+		e.parseDollarInline = value
+	})
+}
+
+// WithBlockDollarParser enables or disables the parsing of $$...$$
+func WithBlockDollarParser(enable ...bool) Option {
+	value := true
+	if len(enable) > 0 {
+		value = enable[0]
+	}
+	return extensionFunc(func(e *Extension) {
+		e.parseDollarBlock = value
+	})
+}
+
+// Math represents a math extension with default rendered delimiters
+var Math = &Extension{
+	enabled:           true,
+	parseDollarBlock:  true,
+	parseDollarInline: true,
+}
+
+// NewExtension creates a new math extension with the provided options
+func NewExtension(opts ...Option) *Extension {
+	r := &Extension{
+		enabled:           true,
+		parseDollarBlock:  true,
+		parseDollarInline: true,
+	}
+
+	for _, o := range opts {
+		o.SetOption(r)
+	}
+	return r
+}
+
+// Extend extends goldmark with our parsers and renderers
+func (e *Extension) Extend(m goldmark.Markdown) {
+	if !e.enabled {
+		return
+	}
+
+	m.Parser().AddOptions(parser.WithBlockParsers(
+		util.Prioritized(NewBlockParser(e.parseDollarBlock), 701),
+	))
+
+	inlines := []util.PrioritizedValue{
+		util.Prioritized(NewInlineBracketParser(), 501),
+	}
+	if e.parseDollarInline {
+		inlines = append(inlines, util.Prioritized(NewInlineDollarParser(), 501))
+	}
+	m.Parser().AddOptions(parser.WithInlineParsers(inlines...))
+
+	m.Renderer().AddOptions(renderer.WithNodeRenderers(
+		util.Prioritized(NewBlockRenderer(), 501),
+		util.Prioritized(NewInlineRenderer(), 502),
+	))
+}

modules/markup/markdown/meta.go

@@ -5,47 +5,101 @@
 package markdown
 
 import (
+	"bytes"
 	"errors"
-	"strings"
+	"unicode"
+	"unicode/utf8"
 
-	"gopkg.in/yaml.v2"
+	"code.gitea.io/gitea/modules/log"
+	"gopkg.in/yaml.v3"
 )
 
-func isYAMLSeparator(line string) bool {
-	line = strings.TrimSpace(line)
-	for i := 0; i < len(line); i++ {
-		if line[i] != '-' {
+func isYAMLSeparator(line []byte) bool {
+	idx := 0
+	for ; idx < len(line); idx++ {
+		if line[idx] >= utf8.RuneSelf {
+			r, sz := utf8.DecodeRune(line[idx:])
+			if !unicode.IsSpace(r) {
+				return false
+			}
+			idx += sz
+			continue
+		}
+		if line[idx] != ' ' {
+			break
+		}
+	}
+	dashCount := 0
+	for ; idx < len(line); idx++ {
+		if line[idx] != '-' {
+			break
+		}
+		dashCount++
+	}
+	if dashCount < 3 {
+		return false
+	}
+	for ; idx < len(line); idx++ {
+		if line[idx] >= utf8.RuneSelf {
+			r, sz := utf8.DecodeRune(line[idx:])
+			if !unicode.IsSpace(r) {
+				return false
+			}
+			idx += sz
+			continue
+		}
+		if line[idx] != ' ' {
 			return false
 		}
 	}
-	return len(line) > 2
+	return true
 }
 
 // ExtractMetadata consumes a markdown file, parses YAML frontmatter,
 // and returns the frontmatter metadata separated from the markdown content
 func ExtractMetadata(contents string, out interface{}) (string, error) {
-	var front, body []string
-	lines := strings.Split(contents, "\n")
-	for idx, line := range lines {
-		if idx == 0 {
-			// First line has to be a separator
+	body, err := ExtractMetadataBytes([]byte(contents), out)
+	return string(body), err
+}
+
+// ExtractMetadata consumes a markdown file, parses YAML frontmatter,
+// and returns the frontmatter metadata separated from the markdown content
+func ExtractMetadataBytes(contents []byte, out interface{}) ([]byte, error) {
+	var front, body []byte
+
+	start, end := 0, len(contents)
+	idx := bytes.IndexByte(contents[start:], '\n')
+	if idx >= 0 {
+		end = start + idx
+	}
+	line := contents[start:end]
+
 	if !isYAMLSeparator(line) {
-				return "", errors.New("frontmatter must start with a separator line")
+		return contents, errors.New("frontmatter must start with a separator line")
 	}
-			continue
+	frontMatterStart := end + 1
+	for start = frontMatterStart; start < len(contents); start = end + 1 {
+		end = len(contents)
+		idx := bytes.IndexByte(contents[start:], '\n')
+		if idx >= 0 {
+			end = start + idx
 		}
+		line := contents[start:end]
 		if isYAMLSeparator(line) {
-			front, body = lines[1:idx], lines[idx+1:]
+			front = contents[frontMatterStart:start]
+			body = contents[end+1:]
 			break
 		}
 	}
 
 	if len(front) == 0 {
-		return "", errors.New("could not determine metadata")
+		return contents, errors.New("could not determine metadata")
 	}
 
-	if err := yaml.Unmarshal([]byte(strings.Join(front, "\n")), out); err != nil {
-		return "", err
+	log.Info("%s", string(front))
+
+	if err := yaml.Unmarshal(front, out); err != nil {
+		return contents, err
 	}
-	return strings.Join(body, "\n"), nil
+	return body, nil
 }

modules/markup/markdown/meta_test.go

@@ -56,6 +56,38 @@ func TestExtractMetadata(t *testing.T) {
 	})
 }
 
+func TestExtractMetadataBytes(t *testing.T) {
+	t.Run("ValidFrontAndBody", func(t *testing.T) {
+		var meta structs.IssueTemplate
+		body, err := ExtractMetadataBytes([]byte(fmt.Sprintf("%s\n%s\n%s\n%s", sepTest, frontTest, sepTest, bodyTest)), &meta)
+		assert.NoError(t, err)
+		assert.Equal(t, bodyTest, body)
+		assert.Equal(t, metaTest, meta)
+		assert.True(t, validateMetadata(meta))
+	})
+
+	t.Run("NoFirstSeparator", func(t *testing.T) {
+		var meta structs.IssueTemplate
+		_, err := ExtractMetadataBytes([]byte(fmt.Sprintf("%s\n%s\n%s", frontTest, sepTest, bodyTest)), &meta)
+		assert.Error(t, err)
+	})
+
+	t.Run("NoLastSeparator", func(t *testing.T) {
+		var meta structs.IssueTemplate
+		_, err := ExtractMetadataBytes([]byte(fmt.Sprintf("%s\n%s\n%s", sepTest, frontTest, bodyTest)), &meta)
+		assert.Error(t, err)
+	})
+
+	t.Run("NoBody", func(t *testing.T) {
+		var meta structs.IssueTemplate
+		body, err := ExtractMetadataBytes([]byte(fmt.Sprintf("%s\n%s\n%s", sepTest, frontTest, sepTest)), &meta)
+		assert.NoError(t, err)
+		assert.Equal(t, "", body)
+		assert.Equal(t, metaTest, meta)
+		assert.True(t, validateMetadata(meta))
+	})
+}
+
 var (
 	sepTest   = "-----"
 	frontTest = `name: Test

modules/markup/markdown/renderconfig.go

@@ -5,12 +5,11 @@
 package markdown
 
 import (
-	"fmt"
 	"strings"
 
+	"code.gitea.io/gitea/modules/log"
 	"github.com/yuin/goldmark/ast"
-	east "github.com/yuin/goldmark/extension/ast"
-	"gopkg.in/yaml.v2"
+	"gopkg.in/yaml.v3"
 )
 
 // RenderConfig represents rendering configuration for this file
@@ -19,48 +18,46 @@ type RenderConfig struct {
 	Icon     string
 	TOC      bool
 	Lang     string
+	yamlNode *yaml.Node
 }
 
-// ToRenderConfig converts a yaml.MapSlice to a RenderConfig
-func (rc *RenderConfig) ToRenderConfig(meta yaml.MapSlice) {
-	if meta == nil {
-		return
+// UnmarshalYAML implement yaml.v3 UnmarshalYAML
+func (rc *RenderConfig) UnmarshalYAML(value *yaml.Node) error {
+	if rc == nil {
+		rc = &RenderConfig{
+			Meta: "table",
+			Icon: "table",
+			Lang: "",
 		}
-	found := false
-	var giteaMetaControl yaml.MapItem
-	for _, item := range meta {
-		strKey, ok := item.Key.(string)
-		if !ok {
-			continue
-		}
-		strKey = strings.TrimSpace(strings.ToLower(strKey))
-		switch strKey {
-		case "gitea":
-			giteaMetaControl = item
-			found = true
-		case "include_toc":
-			val, ok := item.Value.(bool)
-			if !ok {
-				continue
-			}
-			rc.TOC = val
-		case "lang":
-			val, ok := item.Value.(string)
-			if !ok {
-				continue
-			}
-			val = strings.TrimSpace(val)
-			if len(val) == 0 {
-				continue
-			}
-			rc.Lang = val
 	}
+	rc.yamlNode = value
+
+	type basicRenderConfig struct {
+		Gitea *yaml.Node `yaml:"gitea"`
+		TOC   bool       `yaml:"include_toc"`
+		Lang  string     `yaml:"lang"`
 	}
 
-	if found {
-		switch v := giteaMetaControl.Value.(type) {
-		case string:
-			switch v {
+	var basic basicRenderConfig
+
+	err := value.Decode(&basic)
+	if err != nil {
+		return err
+	}
+
+	if basic.Lang != "" {
+		rc.Lang = basic.Lang
+	}
+
+	rc.TOC = basic.TOC
+	if basic.Gitea == nil {
+		return nil
+	}
+
+	var control *string
+	if err := basic.Gitea.Decode(&control); err == nil && control != nil {
+		log.Info("control %v", control)
+		switch strings.TrimSpace(strings.ToLower(*control)) {
 		case "none":
 			rc.Meta = "none"
 		case "table":
@@ -68,20 +65,22 @@ func (rc *RenderConfig) ToRenderConfig(meta yaml.MapSlice) {
 		default: // "details"
 			rc.Meta = "details"
 		}
-		case yaml.MapSlice:
-			for _, item := range v {
-				strKey, ok := item.Key.(string)
-				if !ok {
-					continue
+		return nil
 	}
-				strKey = strings.TrimSpace(strings.ToLower(strKey))
-				switch strKey {
-				case "meta":
-					val, ok := item.Value.(string)
-					if !ok {
-						continue
+
+	type giteaControl struct {
+		Meta string     `yaml:"meta"`
+		Icon string     `yaml:"details_icon"`
+		TOC  *yaml.Node `yaml:"include_toc"`
+		Lang string     `yaml:"lang"`
 	}
-					switch strings.TrimSpace(strings.ToLower(val)) {
+
+	var controlStruct *giteaControl
+	if err := basic.Gitea.Decode(controlStruct); err != nil || controlStruct == nil {
+		return err
+	}
+
+	switch strings.TrimSpace(strings.ToLower(controlStruct.Meta)) {
 	case "none":
 		rc.Meta = "none"
 	case "table":
@@ -89,75 +88,31 @@ func (rc *RenderConfig) ToRenderConfig(meta yaml.MapSlice) {
 	default: // "details"
 		rc.Meta = "details"
 	}
-				case "details_icon":
-					val, ok := item.Value.(string)
-					if !ok {
-						continue
-					}
-					rc.Icon = strings.TrimSpace(strings.ToLower(val))
-				case "include_toc":
-					val, ok := item.Value.(bool)
-					if !ok {
-						continue
-					}
-					rc.TOC = val
-				case "lang":
-					val, ok := item.Value.(string)
-					if !ok {
-						continue
-					}
-					val = strings.TrimSpace(val)
-					if len(val) == 0 {
-						continue
-					}
-					rc.Lang = val
-				}
-			}
+
+	rc.Icon = strings.TrimSpace(strings.ToLower(controlStruct.Icon))
+
+	if controlStruct.Lang != "" {
+		rc.Lang = controlStruct.Lang
 	}
+
+	var toc bool
+	if err := controlStruct.TOC.Decode(&toc); err == nil {
+		rc.TOC = toc
 	}
+
+	return nil
 }
 
-func (rc *RenderConfig) toMetaNode(meta yaml.MapSlice) ast.Node {
+func (rc *RenderConfig) toMetaNode() ast.Node {
+	if rc.yamlNode == nil {
+		return nil
+	}
 	switch rc.Meta {
 	case "table":
-		return metaToTable(meta)
+		return nodeToTable(rc.yamlNode)
 	case "details":
-		return metaToDetails(meta, rc.Icon)
+		return nodeToDetails(rc.yamlNode, rc.Icon)
 	default:
 		return nil
 	}
 }
-
-func metaToTable(meta yaml.MapSlice) ast.Node {
-	table := east.NewTable()
-	alignments := []east.Alignment{}
-	for range meta {
-		alignments = append(alignments, east.AlignNone)
-	}
-	row := east.NewTableRow(alignments)
-	for _, item := range meta {
-		cell := east.NewTableCell()
-		cell.AppendChild(cell, ast.NewString([]byte(fmt.Sprintf("%v", item.Key))))
-		row.AppendChild(row, cell)
-	}
-	table.AppendChild(table, east.NewTableHeader(row))
-
-	row = east.NewTableRow(alignments)
-	for _, item := range meta {
-		cell := east.NewTableCell()
-		cell.AppendChild(cell, ast.NewString([]byte(fmt.Sprintf("%v", item.Value))))
-		row.AppendChild(row, cell)
-	}
-	table.AppendChild(table, row)
-	return table
-}
-
-func metaToDetails(meta yaml.MapSlice, icon string) ast.Node {
-	details := NewDetails()
-	summary := NewSummary()
-	summary.AppendChild(summary, NewIcon(icon))
-	details.AppendChild(details, summary)
-	details.AppendChild(details, metaToTable(meta))
-
-	return details
-}

modules/markup/markdown/renderconfig_test.go

@@ -0,0 +1,162 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package markdown
+
+import (
+	"testing"
+
+	"gopkg.in/yaml.v3"
+)
+
+func TestRenderConfig_UnmarshalYAML(t *testing.T) {
+	tests := []struct {
+		name     string
+		expected *RenderConfig
+		args     string
+	}{
+		{
+			"empty", &RenderConfig{
+				Meta: "table",
+				Icon: "table",
+				Lang: "",
+			}, "",
+		},
+		{
+			"lang", &RenderConfig{
+				Meta: "table",
+				Icon: "table",
+				Lang: "test",
+			}, "lang: test",
+		},
+		{
+			"metatable", &RenderConfig{
+				Meta: "table",
+				Icon: "table",
+				Lang: "",
+			}, "gitea: table",
+		},
+		{
+			"metanone", &RenderConfig{
+				Meta: "none",
+				Icon: "table",
+				Lang: "",
+			}, "gitea: none",
+		},
+		{
+			"metadetails", &RenderConfig{
+				Meta: "details",
+				Icon: "table",
+				Lang: "",
+			}, "gitea: details",
+		},
+		{
+			"metawrong", &RenderConfig{
+				Meta: "details",
+				Icon: "table",
+				Lang: "",
+			}, "gitea: wrong",
+		},
+		{
+			"toc", &RenderConfig{
+				TOC:  true,
+				Meta: "table",
+				Icon: "table",
+				Lang: "",
+			}, "include_toc: true",
+		},
+		{
+			"tocfalse", &RenderConfig{
+				TOC:  false,
+				Meta: "table",
+				Icon: "table",
+				Lang: "",
+			}, "include_toc: false",
+		},
+		{
+			"toclang", &RenderConfig{
+				Meta: "table",
+				Icon: "table",
+				TOC:  true,
+				Lang: "testlang",
+			}, `
+	include_toc: true
+	lang: testlang
+`,
+		},
+		{
+			"complexlang", &RenderConfig{
+				Meta: "table",
+				Icon: "table",
+				Lang: "testlang",
+			}, `
+	gitea:
+		lang: testlang
+`,
+		},
+		{
+			"complexlang2", &RenderConfig{
+				Meta: "table",
+				Icon: "table",
+				Lang: "testlang",
+			}, `
+	lang: notright
+	gitea:
+		lang: testlang
+`,
+		},
+		{
+			"complexlang", &RenderConfig{
+				Meta: "table",
+				Icon: "table",
+				Lang: "testlang",
+			}, `
+	gitea:
+		lang: testlang
+`,
+		},
+		{
+			"complex2", &RenderConfig{
+				Lang: "two",
+				Meta: "table",
+				TOC:  true,
+				Icon: "smiley",
+			}, `
+	lang: one
+	include_toc: true
+	gitea:
+		details_icon: smiley
+		meta: table
+		include_toc: true
+		lang: two
+`,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := &RenderConfig{
+				Meta: "table",
+				Icon: "table",
+				Lang: "",
+			}
+			if err := yaml.Unmarshal([]byte(tt.args), got); err != nil {
+				t.Errorf("RenderConfig.UnmarshalYAML() error = %v", err)
+				return
+			}
+
+			if got.Meta != tt.expected.Meta {
+				t.Errorf("Meta Expected %s Got %s", tt.expected.Meta, got.Meta)
+			}
+			if got.Icon != tt.expected.Icon {
+				t.Errorf("Icon Expected %s Got %s", tt.expected.Icon, got.Icon)
+			}
+			if got.Lang != tt.expected.Lang {
+				t.Errorf("Lang Expected %s Got %s", tt.expected.Lang, got.Lang)
+			}
+			if got.TOC != tt.expected.TOC {
+				t.Errorf("TOC Expected %t Got %t", tt.expected.TOC, got.TOC)
+			}
+		})
+	}
+}

modules/markup/sanitizer.go

@@ -56,7 +56,7 @@ func createDefaultPolicy() *bluemonday.Policy {
 	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^code-block( is-loading)?$`)).OnElements("pre")
 
 	// For Chroma markdown plugin
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^(chroma )?language-[\w-]+$`)).OnElements("code")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^(chroma )?language-[\w-]+( display)?( is-loading)?$`)).OnElements("code")
 
 	// Checkboxes
 	policy.AllowAttrs("type").Matching(regexp.MustCompile(`^checkbox$`)).OnElements("input")
@@ -83,7 +83,7 @@ func createDefaultPolicy() *bluemonday.Policy {
 	policy.AllowAttrs("class").Matching(regexp.MustCompile(`emoji`)).OnElements("img")
 
 	// Allow icons, emojis, chroma syntax and keyword markup on span
-	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^((icon(\s+[\p{L}\p{N}_-]+)+)|(emoji))$|^([a-z][a-z0-9]{0,2})$|^` + keywordClass + `$`)).OnElements("span")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^((icon(\s+[\p{L}\p{N}_-]+)+)|(emoji)|(language-math display)|(language-math inline))$|^([a-z][a-z0-9]{0,2})$|^` + keywordClass + `$`)).OnElements("span")
 
 	// Allow 'style' attribute on text elements.
 	policy.AllowAttrs("style").OnElements("span", "p")

modules/setting/setting.go

@@ -344,10 +344,12 @@ var (
 		EnableHardLineBreakInDocuments bool
 		CustomURLSchemes               []string `ini:"CUSTOM_URL_SCHEMES"`
 		FileExtensions                 []string
+		EnableMath                     bool
 	}{
 		EnableHardLineBreakInComments:  true,
 		EnableHardLineBreakInDocuments: false,
 		FileExtensions:                 strings.Split(".md,.markdown,.mdown,.mkd", ","),
+		EnableMath:                     true,
 	}
 
 	// Admin settings

package-lock.json

@@ -20,6 +20,7 @@
         "font-awesome": "4.7.0",
         "jquery": "3.6.1",
         "jquery.are-you-sure": "1.9.0",
+        "katex": "0.16.2",
         "less": "4.1.3",
         "less-loader": "11.0.0",
         "license-checker-webpack-plugin": "0.2.1",
@@ -7750,6 +7751,29 @@
       "resolved": "https://registry.npmjs.org/just-extend/-/just-extend-5.1.1.tgz",
       "integrity": "sha512-b+z6yF1d4EOyDgylzQo5IminlUmzSeqR1hs/bzjBNjuGras4FXq/6TrzjxfN0j+TmI0ltJzTNlqXUMCniciwKQ=="
     },
+    "node_modules/katex": {
+      "version": "0.16.2",
+      "resolved": "https://registry.npmjs.org/katex/-/katex-0.16.2.tgz",
+      "integrity": "sha512-70DJdQAyh9EMsthw3AaQlDyFf54X7nWEUIa5W+rq8XOpEk//w5Th7/8SqFqpvi/KZ2t6MHUj4f9wLmztBmAYQA==",
+      "funding": [
+        "https://opencollective.com/katex",
+        "https://github.com/sponsors/katex"
+      ],
+      "dependencies": {
+        "commander": "^8.0.0"
+      },
+      "bin": {
+        "katex": "cli.js"
+      }
+    },
+    "node_modules/katex/node_modules/commander": {
+      "version": "8.3.0",
+      "resolved": "https://registry.npmjs.org/commander/-/commander-8.3.0.tgz",
+      "integrity": "sha512-OkTL9umf+He2DZkUq8f8J9of7yL6RJKI24dVITBmNfZBmri9zYZQrKkuXiKhyfPSu8tUhnVBB1iKXevvnlR4Ww==",
+      "engines": {
+        "node": ">= 12"
+      }
+    },
     "node_modules/khroma": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/khroma/-/khroma-2.0.0.tgz",
@@ -17717,6 +17741,21 @@
       "resolved": "https://registry.npmjs.org/just-extend/-/just-extend-5.1.1.tgz",
       "integrity": "sha512-b+z6yF1d4EOyDgylzQo5IminlUmzSeqR1hs/bzjBNjuGras4FXq/6TrzjxfN0j+TmI0ltJzTNlqXUMCniciwKQ=="
     },
+    "katex": {
+      "version": "0.16.2",
+      "resolved": "https://registry.npmjs.org/katex/-/katex-0.16.2.tgz",
+      "integrity": "sha512-70DJdQAyh9EMsthw3AaQlDyFf54X7nWEUIa5W+rq8XOpEk//w5Th7/8SqFqpvi/KZ2t6MHUj4f9wLmztBmAYQA==",
+      "requires": {
+        "commander": "^8.0.0"
+      },
+      "dependencies": {
+        "commander": {
+          "version": "8.3.0",
+          "resolved": "https://registry.npmjs.org/commander/-/commander-8.3.0.tgz",
+          "integrity": "sha512-OkTL9umf+He2DZkUq8f8J9of7yL6RJKI24dVITBmNfZBmri9zYZQrKkuXiKhyfPSu8tUhnVBB1iKXevvnlR4Ww=="
+        }
+      }
+    },
     "khroma": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/khroma/-/khroma-2.0.0.tgz",

package.json

@@ -20,6 +20,7 @@
     "font-awesome": "4.7.0",
     "jquery": "3.6.1",
     "jquery.are-you-sure": "1.9.0",
+    "katex": "0.16.2",
     "less": "4.1.3",
     "less-loader": "11.0.0",
     "license-checker-webpack-plugin": "0.2.1",

web_src/js/markup/content.js

@@ -1,10 +1,12 @@
 import {renderMermaid} from './mermaid.js';
+import {renderMath} from './math.js';
 import {renderCodeCopy} from './codecopy.js';
 import {initMarkupTasklist} from './tasklist.js';
 
 // code that runs for all markup content
 export function initMarkupContent() {
   renderMermaid();
+  renderMath();
   renderCodeCopy();
 }
 

web_src/js/markup/math.js

@@ -0,0 +1,37 @@
+function displayError(el, err) {
+  const target = targetElement(el);
+  target.remove('is-loading');
+  const errorNode = document.createElement('div');
+  errorNode.setAttribute('class', 'ui message error markup-block-error mono');
+  errorNode.textContent = err.str || err.message || String(err);
+  target.before(errorNode);
+}
+
+function targetElement(el) {
+  // The target element is either the current element if it has the `is-loading` class or the pre that contains it
+  return el.classList.contains('is-loading') ? el : el.closest('pre');
+}
+
+export async function renderMath() {
+  const els = document.querySelectorAll('.markup code.language-math');
+  if (!els.length) return;
+
+  const [{default: katex}] = await Promise.all([
+    import(/* webpackChunkName: "katex" */'katex'),
+    import(/* webpackChunkName: "katex" */'katex/dist/katex.css'),
+  ]);
+
+  for (const el of els) {
+    const source = el.textContent;
+    const options = {display: el.classList.contains('display')};
+
+    try {
+      const markup = katex.renderToString(source, options);
+      const tempEl = document.createElement(options.display ? 'p' : 'span');
+      tempEl.innerHTML = markup;
+      targetElement(el).replaceWith(tempEl);
+    } catch (error) {
+      displayError(el, error);
+    }
+  }
+}

web_src/less/animations.less

@@ -33,6 +33,13 @@
   height: var(--height-loading);
 }
 
+code.language-math.is-loading::after {
+  padding: 0;
+  border-width: 2px;
+  width: 1.25rem;
+  height: 1.25rem;
+}
+
 @keyframes fadein {
   0% {
     opacity: 0;

webpack.config.js

@@ -37,6 +37,10 @@ const filterCssImport = (url, ...args) => {
     if (/(eot|ttf|otf|woff|svg)$/.test(importedFile)) return false;
   }
 
+  if (cssFile.includes('katex') && /(ttf|woff)$/.test(importedFile)) {
+    return false;
+  }
+
   if (cssFile.includes('font-awesome') && /(eot|ttf|otf|woff|svg)$/.test(importedFile)) {
     return false;
   }