Fix markdown preview $$ support (#31514)

close #31481

currently `$$A + B$$ test` will ignore text after $$ block

test text

![圖片](https://github.com/go-gitea/gitea/assets/30816317/39b2974b-c0b6-48a0-87d0-5f4a13615eed)

before fix

![圖片](https://github.com/go-gitea/gitea/assets/30816317/15469e4c-474d-4128-b46f-d6cadaafbd68)

after fix

![圖片](https://github.com/go-gitea/gitea/assets/30816317/c1025eef-177f-4ade-988f-510e7039f3f9)

github display

![圖片](https://github.com/go-gitea/gitea/assets/30816317/97cd1e10-ac94-4899-86d8-8e359ef1d694)

(cherry picked from commit f0033051d5ce07f5a18d2aacef6bfdca5fc69014)

modules/markup/markdown/markdown_test.go

@@ -552,6 +552,14 @@ func TestMathBlock(t *testing.T) {
 			"$a$ ($b$) [$c$] {$d$}",
 			`<p><code class="language-math is-loading">a</code> (<code class="language-math is-loading">b</code>) [$c$] {$d$}</p>` + nl,
 		},
+		{
+			"$$a$$ test",
+			`<p><code class="language-math display is-loading">a</code> test</p>` + nl,
+		},
+		{
+			"test $$a$$",
+			`<p>test <code class="language-math display is-loading">a</code></p>` + nl,
+		},
 	}
 
 	for _, test := range testcases {

modules/markup/markdown/math/block_parser.go

@@ -47,6 +47,12 @@ func (b *blockParser) Open(parent ast.Node, reader text.Reader, pc parser.Contex
 	}
 	idx := bytes.Index(line[pos+2:], endBytes)
 	if idx >= 0 {
+		// for case $$ ... $$ any other text
+		for i := pos + idx + 4; i < len(line); i++ {
+			if line[i] != ' ' && line[i] != '\n' {
+				return nil, parser.NoChildren
+			}
+		}
 		segment.Stop = segment.Start + idx + 2
 		reader.Advance(segment.Len() - 1)
 		segment.Start += 2

modules/markup/markdown/math/inline_block_node.go

@@ -0,0 +1,31 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package math
+
+import (
+	"github.com/yuin/goldmark/ast"
+)
+
+// InlineBlock represents inline math e.g. $$...$$
+type InlineBlock struct {
+	Inline
+}
+
+// InlineBlock implements InlineBlock.
+func (n *InlineBlock) InlineBlock() {}
+
+// KindInlineBlock is the kind for math inline block
+var KindInlineBlock = ast.NewNodeKind("MathInlineBlock")
+
+// Kind returns KindInlineBlock
+func (n *InlineBlock) Kind() ast.NodeKind {
+	return KindInlineBlock
+}
+
+// NewInlineBlock creates a new ast math inline block node
+func NewInlineBlock() *InlineBlock {
+	return &InlineBlock{
+		Inline{},
+	}
+}

modules/markup/markdown/math/inline_parser.go

@@ -21,11 +21,20 @@ var defaultInlineDollarParser = &inlineParser{
 	end:   []byte{'$'},
 }
 
+var defaultDualDollarParser = &inlineParser{
+	start: []byte{'$', '$'},
+	end:   []byte{'$', '$'},
+}
+
 // NewInlineDollarParser returns a new inline parser
 func NewInlineDollarParser() parser.InlineParser {
 	return defaultInlineDollarParser
 }
 
+func NewInlineDualDollarParser() parser.InlineParser {
+	return defaultDualDollarParser
+}
+
 var defaultInlineBracketParser = &inlineParser{
 	start: []byte{'\\', '('},
 	end:   []byte{'\\', ')'},
@@ -38,7 +47,7 @@ func NewInlineBracketParser() parser.InlineParser {
 
 // Trigger triggers this parser on $ or \
 func (parser *inlineParser) Trigger() []byte {
-	return parser.start[0:1]
+	return parser.start
 }
 
 func isPunctuation(b byte) bool {
@@ -88,7 +97,11 @@ func (parser *inlineParser) Parse(parent ast.Node, block text.Reader, pc parser.
 			break
 		}
 		suceedingCharacter := line[pos]
-		if !isPunctuation(suceedingCharacter) && !(suceedingCharacter == ' ') && !isBracket(suceedingCharacter) {
+		// check valid ending character
+		if !isPunctuation(suceedingCharacter) &&
+			!(suceedingCharacter == ' ') &&
+			!(suceedingCharacter == '\n') &&
+			!isBracket(suceedingCharacter) {
 			return nil
 		}
 		if line[ender-1] != '\\' {
@@ -101,12 +114,21 @@ func (parser *inlineParser) Parse(parent ast.Node, block text.Reader, pc parser.
 
 	block.Advance(opener)
 	_, pos := block.Position()
-	node := NewInline()
+	var node ast.Node
+	if parser == defaultDualDollarParser {
+		node = NewInlineBlock()
+	} else {
+		node = NewInline()
+	}
 	segment := pos.WithStop(pos.Start + ender - opener)
 	node.AppendChild(node, ast.NewRawTextSegment(segment))
 	block.Advance(ender - opener + len(parser.end))
 
-	trimBlock(node, block)
+	if parser == defaultDualDollarParser {
+		trimBlock(&(node.(*InlineBlock)).Inline, block)
+	} else {
+		trimBlock(node.(*Inline), block)
+	}
 	return node
 }
 

modules/markup/markdown/math/inline_renderer.go

@@ -21,7 +21,11 @@ func NewInlineRenderer() renderer.NodeRenderer {
 
 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">`)
+		extraClass := ""
+		if _, ok := n.(*InlineBlock); ok {
+			extraClass = "display "
+		}
+		_, _ = w.WriteString(`<code class="language-math ` + extraClass + `is-loading">`)
 		for c := n.FirstChild(); c != nil; c = c.NextSibling() {
 			segment := c.(*ast.Text).Segment
 			value := util.EscapeHTML(segment.Value(source))
@@ -43,4 +47,5 @@ func (r *InlineRenderer) renderInline(w util.BufWriter, source []byte, n ast.Nod
 // RegisterFuncs registers the renderer for inline math nodes
 func (r *InlineRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
 	reg.Register(KindInline, r.renderInline)
+	reg.Register(KindInlineBlock, r.renderInline)
 }

modules/markup/markdown/math/math.go

@@ -96,7 +96,8 @@ func (e *Extension) Extend(m goldmark.Markdown) {
 		util.Prioritized(NewInlineBracketParser(), 501),
 	}
 	if e.parseDollarInline {
-		inlines = append(inlines, util.Prioritized(NewInlineDollarParser(), 501))
+		inlines = append(inlines, util.Prioritized(NewInlineDollarParser(), 503),
+			util.Prioritized(NewInlineDualDollarParser(), 502))
 	}
 	m.Parser().AddOptions(parser.WithInlineParsers(inlines...))