Change markdown rendering from blackfriday to goldmark (#9533)

* Move to goldmark

Markdown rendering moved from blackfriday to the goldmark.

Multiple subtle changes required to the goldmark extensions to keep
current rendering and defaults.

Can go further with goldmark linkify and have this work within markdown
rendering making the link processor unnecessary.

Need to think about how to go about allowing extensions - at present it
seems that these would be hard to do without recompilation.

* linter fixes

Co-authored-by: Lauris BH <lauris@nix.lv>

vendor/github.com/yuin/goldmark/parser/raw_html.go

@@ -0,0 +1,108 @@
+package parser
+
+import (
+	"bytes"
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+	"regexp"
+)
+
+type rawHTMLParser struct {
+}
+
+var defaultRawHTMLParser = &rawHTMLParser{}
+
+// NewRawHTMLParser return a new InlineParser that can parse
+// inline htmls
+func NewRawHTMLParser() InlineParser {
+	return defaultRawHTMLParser
+}
+
+func (s *rawHTMLParser) Trigger() []byte {
+	return []byte{'<'}
+}
+
+func (s *rawHTMLParser) Parse(parent ast.Node, block text.Reader, pc Context) ast.Node {
+	line, _ := block.PeekLine()
+	if len(line) > 1 && util.IsAlphaNumeric(line[1]) {
+		return s.parseMultiLineRegexp(openTagRegexp, block, pc)
+	}
+	if len(line) > 2 && line[1] == '/' && util.IsAlphaNumeric(line[2]) {
+		return s.parseMultiLineRegexp(closeTagRegexp, block, pc)
+	}
+	if bytes.HasPrefix(line, []byte("<!--")) {
+		return s.parseMultiLineRegexp(commentRegexp, block, pc)
+	}
+	if bytes.HasPrefix(line, []byte("<?")) {
+		return s.parseSingleLineRegexp(processingInstructionRegexp, block, pc)
+	}
+	if len(line) > 2 && line[1] == '!' && line[2] >= 'A' && line[2] <= 'Z' {
+		return s.parseSingleLineRegexp(declRegexp, block, pc)
+	}
+	if bytes.HasPrefix(line, []byte("<![CDATA[")) {
+		return s.parseMultiLineRegexp(cdataRegexp, block, pc)
+	}
+	return nil
+}
+
+var tagnamePattern = `([A-Za-z][A-Za-z0-9-]*)`
+var attributePattern = `(?:\s+[a-zA-Z_:][a-zA-Z0-9:._-]*(?:\s*=\s*(?:[^\"'=<>` + "`" + `\x00-\x20]+|'[^']*'|"[^"]*"))?)`
+var openTagRegexp = regexp.MustCompile("^<" + tagnamePattern + attributePattern + `*\s*/?>`)
+var closeTagRegexp = regexp.MustCompile("^</" + tagnamePattern + `\s*>`)
+var commentRegexp = regexp.MustCompile(`^<!---->|<!--(?:-?[^>-])(?:-?[^-])*-->`)
+var processingInstructionRegexp = regexp.MustCompile(`^(?:<\?).*?(?:\?>)`)
+var declRegexp = regexp.MustCompile(`^<![A-Z]+\s+[^>]*>`)
+var cdataRegexp = regexp.MustCompile(`<!\[CDATA\[[\s\S]*?\]\]>`)
+
+func (s *rawHTMLParser) parseSingleLineRegexp(reg *regexp.Regexp, block text.Reader, pc Context) ast.Node {
+	line, segment := block.PeekLine()
+	match := reg.FindSubmatchIndex(line)
+	if match == nil {
+		return nil
+	}
+	node := ast.NewRawHTML()
+	node.Segments.Append(segment.WithStop(segment.Start + match[1]))
+	block.Advance(match[1])
+	return node
+}
+
+var dummyMatch = [][]byte{}
+
+func (s *rawHTMLParser) parseMultiLineRegexp(reg *regexp.Regexp, block text.Reader, pc Context) ast.Node {
+	sline, ssegment := block.Position()
+	if block.Match(reg) {
+		node := ast.NewRawHTML()
+		eline, esegment := block.Position()
+		block.SetPosition(sline, ssegment)
+		for {
+			line, segment := block.PeekLine()
+			if line == nil {
+				break
+			}
+			l, _ := block.Position()
+			start := segment.Start
+			if l == sline {
+				start = ssegment.Start
+			}
+			end := segment.Stop
+			if l == eline {
+				end = esegment.Start
+			}
+
+			node.Segments.Append(text.NewSegment(start, end))
+			if l == eline {
+				block.Advance(end - start)
+				break
+			} else {
+				block.AdvanceLine()
+			}
+		}
+		return node
+	}
+	return nil
+}
+
+func (s *rawHTMLParser) CloseBlock(parent ast.Node, pc Context) {
+	// nothing to do
+}