feat: add GitHub Alerts transformer and renderers

Co-Authored-By: Manuel Rüger <manuel@rueg.eu>

renderer/text_legacy.go

@@ -0,0 +1,90 @@
+package renderer
+
+import (
+	"unicode/utf8"
+
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/renderer"
+	"github.com/yuin/goldmark/renderer/html"
+	"github.com/yuin/goldmark/util"
+)
+
+// ConfluenceTextLegacyRenderer slightly alters the default goldmark behavior for
+// inline text block. It allows for soft breaks
+// (c.f. https://spec.commonmark.org/0.30/#softbreak)
+// to be rendered into HTML as either '\n' (the goldmark default)
+// or as ' '.
+// This latter option is useful for Confluence,
+// which inserts <br> tags into uploaded HTML where it sees '\n'.
+// See also https://sembr.org/ for partial motivation.
+type ConfluenceTextLegacyRenderer struct {
+	html.Config
+	softBreak rune
+}
+
+// NewConfluenceTextLegacyRenderer creates a new instance of the ConfluenceTextRenderer (legacy version)
+func NewConfluenceTextLegacyRenderer(stripNL bool, opts ...html.Option) renderer.NodeRenderer {
+	sb := '\n'
+	if stripNL {
+		sb = ' '
+	}
+	return &ConfluenceTextLegacyRenderer{
+		Config:    html.NewConfig(),
+		softBreak: sb,
+	}
+}
+
+// RegisterFuncs implements NodeRenderer.RegisterFuncs .
+func (r *ConfluenceTextLegacyRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	reg.Register(ast.KindText, r.renderText)
+}
+
+// This is taken from https://github.com/yuin/goldmark/blob/v1.6.0/renderer/html/html.go#L719
+// with the hardcoded '\n' for soft breaks swapped for the configurable r.softBreak
+func (r *ConfluenceTextLegacyRenderer) renderText(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
+	if !entering {
+		return ast.WalkContinue, nil
+	}
+	n := node.(*ast.Text)
+	segment := n.Segment
+	if n.IsRaw() {
+		r.Writer.RawWrite(w, segment.Value(source))
+	} else {
+		value := segment.Value(source)
+		r.Writer.Write(w, value)
+		if n.HardLineBreak() || (n.SoftLineBreak() && r.HardWraps) {
+			if r.XHTML {
+				_, _ = w.WriteString("<br />\n")
+			} else {
+				_, _ = w.WriteString("<br>\n")
+			}
+		} else if n.SoftLineBreak() {
+			if r.EastAsianLineBreaks != html.EastAsianLineBreaksNone && len(value) != 0 {
+				sibling := node.NextSibling()
+				if sibling != nil && sibling.Kind() == ast.KindText {
+					if siblingText := sibling.(*ast.Text).Value(source); len(siblingText) != 0 {
+						thisLastRune := util.ToRune(value, len(value)-1)
+						siblingFirstRune, _ := utf8.DecodeRune(siblingText)
+						// Inline the softLineBreak function as it's not public
+						writeLineBreak := false
+						switch r.EastAsianLineBreaks {
+						case html.EastAsianLineBreaksNone:
+							writeLineBreak = false
+						case html.EastAsianLineBreaksSimple:
+							writeLineBreak = !util.IsEastAsianWideRune(thisLastRune) || !util.IsEastAsianWideRune(siblingFirstRune)
+						case html.EastAsianLineBreaksCSS3Draft:
+							writeLineBreak = eastAsianLineBreaksCSS3DraftSoftLineBreak(thisLastRune, siblingFirstRune)
+						}
+
+						if writeLineBreak {
+							_ = w.WriteByte(byte(r.softBreak))
+						}
+					}
+				}
+			} else {
+				_ = w.WriteByte(byte(r.softBreak))
+			}
+		}
+	}
+	return ast.WalkContinue, nil
+}