Add Math support (MathJaX) to blackfriday.v2

.gitignore

@@ -5,4 +5,4 @@
 _obj
 _test*
 markdown
-tags
+tags

README.md

@@ -184,11 +184,11 @@ implements the following extensions:
     and supply a language (to make syntax highlighting simple). Just
     mark it like this:
 
-        ```go
+        ​```go
         func getTrue() bool {
             return true
         }
-        ```
+        ​```
 
     You can use 3 or more backticks to mark the beginning of the
     block, and the same number to mark the end of the block.
@@ -209,7 +209,7 @@ implements the following extensions:
     end of the document. A footnote looks like this:
 
         This is a footnote.[^1]
-        
+
         [^1]: the footnote text.
 
 *   **Autolinking**. Blackfriday can find URLs that have not been
@@ -237,6 +237,24 @@ implements the following extensions:
     becomes `<sup>4</sup>&frasl;<sub>5</sub>`, which renders as
     <sup>4</sup>&frasl;<sub>5</sub>.
 
+*   **MathJaX Support** is an additional feature which is supported by
+    many markdown editor. It translate inline math equation quoted by `$`
+    and display math block quoted by `$$` into MathJax compatible format.
+    hyphen `_` won't break LaTeX render within a math element any more.
+    ```
+    $$
+    \left[ \begin{array}{a} a^l_1 \\ ⋮ \\ a^l_{d_l} \end{array}\right]
+    = \sigma(
+     \left[ \begin{matrix} 
+     	w^l_{1,1} & ⋯  & w^l_{1,d_{l-1}} \\  
+     	⋮ & ⋱  & ⋮  \\ 
+     	w^l_{d_l,1} & ⋯  & w^l_{d_l,d_{l-1}} \\  
+     \end{matrix}\right]  ·
+     \left[ \begin{array}{x} a^{l-1}_1 \\ ⋮ \\ ⋮ \\ a^{l-1}_{d_{l-1}} \end{array}\right] + 
+     \left[ \begin{array}{b} b^l_1 \\ ⋮ \\ b^l_{d_l} \end{array}\right])
+     $$
+    ```
+
 
 Other renderers
 ---------------
@@ -275,9 +293,9 @@ License
 [Blackfriday is distributed under the Simplified BSD License](LICENSE.txt)
 
 
-   [1]: https://daringfireball.net/projects/markdown/ "Markdown"
-   [2]: https://golang.org/ "Go Language"
-   [3]: https://github.com/vmg/sundown "Sundown"
-   [4]: https://godoc.org/gopkg.in/russross/blackfriday.v2#Parse "Parse func"
-   [5]: https://github.com/microcosm-cc/bluemonday "Bluemonday"
-   [6]: https://labix.org/gopkg.in "gopkg.in"
+[1]: https://daringfireball.net/projects/markdown/ "Markdown"
+[2]: https://golang.org/ "Go Language"
+[3]: https://github.com/vmg/sundown "Sundown"
+[4]: https://godoc.org/gopkg.in/russross/blackfriday.v2#Parse "Parse func"
+[5]: https://github.com/microcosm-cc/bluemonday "Bluemonday"
+[6]: https://labix.org/gopkg.in "gopkg.in"

block.go

@@ -189,6 +189,14 @@ func (p *Markdown) block(data []byte) {
 			}
 		}
 
+		// handle math block
+		if p.extensions&MathJaxSupport != 0 {
+			if i := p.blockMath(data); i > 0 {
+				data = data[i:]
+				continue
+			}
+		}
+
 		// anything else must look like a normal paragraph
 		// note: this finds underlined headings, too
 		data = data[p.paragraph(data):]
@@ -239,7 +247,7 @@ func (p *Markdown) prefixHeading(data []byte) int {
 		}
 		// extract heading id iff found
 		if j < end && k < end {
-			id = string(data[j+2 : k])
+			id = string(data[j+2: k])
 			end = j
 			skip = k + 1
 			for end > 0 && data[end-1] == ' ' {
@@ -597,7 +605,7 @@ func isFenceLine(data []byte, syntax *string, oldmarker string) (end int, marker
 	if size < 3 {
 		return 0, ""
 	}
-	marker = string(data[i-size : i])
+	marker = string(data[i-size: i])
 
 	// if this is the end marker, it must match the beginning marker
 	if oldmarker != "" && marker != oldmarker {
@@ -651,7 +659,7 @@ func isFenceLine(data []byte, syntax *string, oldmarker string) (end int, marker
 			}
 		}
 
-		*syntax = string(data[syntaxStart : syntaxStart+syn])
+		*syntax = string(data[syntaxStart: syntaxStart+syn])
 	}
 
 	i = skipChar(data, i, ' ')
@@ -1277,7 +1285,7 @@ gatherlines:
 			}
 		}
 
-		chunk := data[line+indentIndex : i]
+		chunk := data[line+indentIndex: i]
 
 		// evaluate how this line fits in
 		switch {
@@ -1301,7 +1309,7 @@ gatherlines:
 				sublist = raw.Len()
 			}
 
-		// is this a nested prefix heading?
+			// is this a nested prefix heading?
 		case p.isPrefixHeading(chunk):
 			// if the heading is not indented, it is not nested in the list
 			// and thus ends the list
@@ -1311,9 +1319,9 @@ gatherlines:
 			}
 			*flags |= ListItemContainsBlock
 
-		// anything following an empty line is only part
-		// of this item if it is indented 4 spaces
-		// (regardless of the indentation of the beginning of the item)
+			// anything following an empty line is only part
+			// of this item if it is indented 4 spaces
+			// (regardless of the indentation of the beginning of the item)
 		case containsBlankLine && indent < 4:
 			if *flags&ListTypeDefinition != 0 && i < len(data)-1 {
 				// is the next item still a part of this list?
@@ -1332,7 +1340,7 @@ gatherlines:
 			}
 			break gatherlines
 
-		// a blank line means this should be parsed as a block
+			// a blank line means this should be parsed as a block
 		case containsBlankLine:
 			raw.WriteByte('\n')
 			*flags |= ListItemContainsBlock
@@ -1346,7 +1354,7 @@ gatherlines:
 		}
 
 		// add the line into the working buffer without prefix
-		raw.Write(data[line+indentIndex : i])
+		raw.Write(data[line+indentIndex: i])
 
 		line = i
 	}
@@ -1408,6 +1416,29 @@ func (p *Markdown) renderParagraph(data []byte) {
 	p.addBlock(Paragraph, data[beg:end])
 }
 
+// blockMath handle block surround with $$
+func (p *Markdown) blockMath(data []byte) int {
+	if len(data) <= 4 || data[0] != '$' || data[1] != '$' || data[2] == '$' {
+		return 0
+	}
+
+	// find next $$
+	var end int
+	for end = 2; end+1 < len(data) && (data[end] != '$' || data[end+1] != '$'); end++ {
+	}
+
+	// $$ not match
+	if end+1 == len(data) {
+		return 0
+	}
+
+	// render the display math
+	container := p.addChild(MathBlock, 0)
+	container.Literal = data[2:end]
+
+	return end + 2
+}
+
 func (p *Markdown) paragraph(data []byte) int {
 	// prev: index of 1st char of previous line
 	// line: index of 1st char of current line

block_test.go

@@ -1458,6 +1458,16 @@ func TestFencedCodeBlock_EXTENSION_NO_EMPTY_LINE_BEFORE_BLOCK(t *testing.T) {
 	doTestsBlock(t, tests, FencedCode|NoEmptyLineBeforeBlock)
 }
 
+func TestMathBlock(t *testing.T) {
+	var tests = []string{
+		"$y=a+b$$",
+		"<p><span class=\"math inline\">\\(y=a+b\\)</span>$</p>\n",
+		"$$y_2=a_3+b_4$$",
+		"<p><span class=\"math display\">\\[y_2=a_3+b_4\\]</span></p>",
+	}
+	doTestsBlock(t, tests, CommonExtensions)
+}
+
 func TestTitleBlock_EXTENSION_TITLEBLOCK(t *testing.T) {
 	var tests = []string{
 		"% Some title\n" +

html.go

@@ -46,6 +46,7 @@ const (
 	SmartypantsAngledQuotes                       // Enable angled double quotes (with Smartypants) for double quotes rendering
 	SmartypantsQuotesNBSP                         // Enable « French guillemets » (with Smartypants)
 	TOC                                           // Generate a table of contents
+	MathJaxFromCDN                                // Import MathJax js from CDN
 )
 
 var (
@@ -454,6 +455,10 @@ var (
 	h5CloseTag         = []byte("</h5>")
 	h6Tag              = []byte("<h6")
 	h6CloseTag         = []byte("</h6>")
+	mathTag            = []byte(`<span class="math inline">\(`)
+	mathCloseTag       = []byte(`\)</span>`)
+	blockMathTag       = []byte(`<p><span class="math display">\[`)
+	blockMathCloseTag  = []byte(`\]</span></p>`)
 
 	footnotesDivBytes      = []byte("\n<div class=\"footnotes\">\n\n")
 	footnotesCloseDivBytes = []byte("\n</div>\n")
@@ -815,6 +820,14 @@ func (r *HTMLRenderer) RenderNode(w io.Writer, node *Node, entering bool) WalkSt
 			r.out(w, trCloseTag)
 			r.cr(w)
 		}
+	case Math:
+		r.out(w, mathTag)
+		escapeHTML(w, node.Literal)
+		r.out(w, mathCloseTag)
+	case MathBlock:
+		r.out(w, blockMathTag)
+		escapeHTML(w, node.Literal)
+		r.out(w, blockMathCloseTag)
 	default:
 		panic("Unknown node type " + node.Type.String())
 	}
@@ -881,6 +894,9 @@ func (r *HTMLRenderer) writeDocumentHeader(w io.Writer) {
 		io.WriteString(w, ending)
 		io.WriteString(w, ">\n")
 	}
+	if r.Flags&MathJaxFromCDN != 0 {
+		io.WriteString(w,`<script src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS_CHTML-full""></script>`)
+	}
 	io.WriteString(w, "</head>\n")
 	io.WriteString(w, "<body>\n\n")
 }

inline.go

@@ -187,7 +187,7 @@ func lineBreak(p *Markdown, data []byte, offset int) (int, *Node) {
 type linkType int
 
 const (
-	linkNormal linkType = iota
+	linkNormal           linkType = iota
 	linkImg
 	linkDeferredFootnote
 	linkInlineFootnote
@@ -227,20 +227,20 @@ func link(p *Markdown, data []byte, offset int) (int, *Node) {
 	// an exclamation point)
 	case p.extensions&Footnotes != 0 && len(data)-1 > offset && data[offset+1] == '^':
 		t = linkDeferredFootnote
-	// ![alt] == image
+		// ![alt] == image
 	case offset >= 0 && data[offset] == '!':
 		t = linkImg
 		offset++
-	// ^[text] == inline footnote
-	// [^refId] == deferred footnote
+		// ^[text] == inline footnote
+		// [^refId] == deferred footnote
 	case p.extensions&Footnotes != 0:
 		if offset >= 0 && data[offset] == '^' {
 			t = linkInlineFootnote
 			offset++
 		} else if len(data)-1 > offset && data[offset+1] == '^' {
 			t = linkDeferredFootnote
 		}
-	// [text] == regular link
+		// [text] == regular link
 	default:
 		t = linkNormal
 	}
@@ -385,7 +385,7 @@ func link(p *Markdown, data []byte, offset int) (int, *Node) {
 
 		i++
 
-	// reference style link
+		// reference style link
 	case isReferenceStyleLink(data, i, t):
 		var id []byte
 		altContentConsidered := false
@@ -438,7 +438,7 @@ func link(p *Markdown, data []byte, offset int) (int, *Node) {
 		}
 		i++
 
-	// shortcut reference style link or reference or inline footnote
+		// shortcut reference style link or reference or inline footnote
 	default:
 		var id []byte
 
@@ -607,7 +607,7 @@ type autolinkType int
 
 // These are the possible flag values for the autolink renderer.
 const (
-	notAutolink autolinkType = iota
+	notAutolink    autolinkType = iota
 	normalAutolink
 	emailAutolink
 )
@@ -1203,6 +1203,31 @@ func helperTripleEmphasis(p *Markdown, data []byte, offset int, c byte) (int, *N
 	return 0, nil
 }
 
+// math handle inline math wrapped with '$'
+func math(p *Markdown, data []byte, offset int) (int, *Node) {
+	data = data[offset:]
+
+	// too short, or block math
+	if len(data) <= 2 || data[1] == '$' {
+		return 0, nil
+	}
+
+	// find next '$'
+	var end int
+	for end = 1; end < len(data) && data[end] != '$'; end++ {
+	}
+
+	// $ not match
+	if end == len(data) {
+		return 0, nil
+	}
+
+	// create inline math node
+	math := NewNode(Math)
+	math.Literal = data[1:end]
+	return end + 1, math
+}
+
 func text(s []byte) *Node {
 	node := NewNode(Text)
 	node.Literal = s

inline_test.go

@@ -1165,6 +1165,14 @@ func TestSkipHTML(t *testing.T) {
 	}, TestParams{HTMLFlags: SkipHTML})
 }
 
+func TestInlineMath(t *testing.T) {
+	doTestsParam(t, []string{
+		"$a_b$",
+		`<p><span class="math inline">\(a_b\)</span></p>
+`,
+	}, TestParams{HTMLFlags: SkipHTML, extensions: CommonExtensions})
+}
+
 func BenchmarkSmartDoubleQuotes(b *testing.B) {
 	params := TestParams{HTMLFlags: Smartypants}
 	params.extensions |= Autolink | Strikethrough