Handle yaml frontmatter (#11016)

Add goldmark-meta to render yaml frontmatter as a table

Fix #5377

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

vendor/github.com/yuin/goldmark-meta/meta.go

@@ -0,0 +1,218 @@
+// package meta is a extension for the goldmark(http://github.com/yuin/goldmark).
+//
+// This extension parses YAML metadata blocks and store metadata to a
+// parser.Context.
+package meta
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/yuin/goldmark"
+	gast "github.com/yuin/goldmark/ast"
+	east "github.com/yuin/goldmark/extension/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+
+	"gopkg.in/yaml.v2"
+)
+
+type data struct {
+	Map   map[string]interface{}
+	Items yaml.MapSlice
+	Error error
+	Node  gast.Node
+}
+
+var contextKey = parser.NewContextKey()
+
+// Get returns a YAML metadata.
+func Get(pc parser.Context) map[string]interface{} {
+	v := pc.Get(contextKey)
+	if v == nil {
+		return nil
+	}
+	d := v.(*data)
+	return d.Map
+}
+
+// GetItems returns a YAML metadata.
+// GetItems preserves defined key order.
+func GetItems(pc parser.Context) yaml.MapSlice {
+	v := pc.Get(contextKey)
+	if v == nil {
+		return nil
+	}
+	d := v.(*data)
+	return d.Items
+}
+
+type metaParser struct {
+}
+
+var defaultMetaParser = &metaParser{}
+
+// NewParser returns a BlockParser that can parse YAML metadata blocks.
+func NewParser() parser.BlockParser {
+	return defaultMetaParser
+}
+
+func isSeparator(line []byte) bool {
+	line = util.TrimRightSpace(util.TrimLeftSpace(line))
+	for i := 0; i < len(line); i++ {
+		if line[i] != '-' {
+			return false
+		}
+	}
+	return true
+}
+
+func (b *metaParser) Trigger() []byte {
+	return []byte{'-'}
+}
+
+func (b *metaParser) Open(parent gast.Node, reader text.Reader, pc parser.Context) (gast.Node, parser.State) {
+	linenum, _ := reader.Position()
+	if linenum != 0 {
+		return nil, parser.NoChildren
+	}
+	line, _ := reader.PeekLine()
+	if isSeparator(line) {
+		return gast.NewTextBlock(), parser.NoChildren
+	}
+	return nil, parser.NoChildren
+}
+
+func (b *metaParser) Continue(node gast.Node, reader text.Reader, pc parser.Context) parser.State {
+	line, segment := reader.PeekLine()
+	if isSeparator(line) {
+		reader.Advance(segment.Len())
+		return parser.Close
+	}
+	node.Lines().Append(segment)
+	return parser.Continue | parser.NoChildren
+}
+
+func (b *metaParser) Close(node gast.Node, reader text.Reader, pc parser.Context) {
+	lines := node.Lines()
+	var buf bytes.Buffer
+	for i := 0; i < lines.Len(); i++ {
+		segment := lines.At(i)
+		buf.Write(segment.Value(reader.Source()))
+	}
+	d := &data{}
+	d.Node = node
+	meta := map[string]interface{}{}
+	if err := yaml.Unmarshal(buf.Bytes(), &meta); err != nil {
+		d.Error = err
+	} else {
+		d.Map = meta
+	}
+
+	metaMapSlice := yaml.MapSlice{}
+	if err := yaml.Unmarshal(buf.Bytes(), &metaMapSlice); err != nil {
+		d.Error = err
+	} else {
+		d.Items = metaMapSlice
+	}
+
+	pc.Set(contextKey, d)
+
+	if d.Error == nil {
+		node.Parent().RemoveChild(node.Parent(), node)
+	}
+}
+
+func (b *metaParser) CanInterruptParagraph() bool {
+	return false
+}
+
+func (b *metaParser) CanAcceptIndentedLine() bool {
+	return false
+}
+
+type astTransformer struct {
+}
+
+var defaultASTTransformer = &astTransformer{}
+
+func (a *astTransformer) Transform(node *gast.Document, reader text.Reader, pc parser.Context) {
+	dtmp := pc.Get(contextKey)
+	if dtmp == nil {
+		return
+	}
+	d := dtmp.(*data)
+	if d.Error != nil {
+		msg := gast.NewString([]byte(fmt.Sprintf("<!-- %s -->", d.Error)))
+		msg.SetCode(true)
+		d.Node.AppendChild(d.Node, msg)
+		return
+	}
+
+	meta := GetItems(pc)
+	if meta == nil {
+		return
+	}
+	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, gast.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, gast.NewString([]byte(fmt.Sprintf("%v", item.Value))))
+		row.AppendChild(row, cell)
+	}
+	table.AppendChild(table, row)
+	node.InsertBefore(node, node.FirstChild(), table)
+}
+
+// Option is a functional option type for this extension.
+type Option func(*meta)
+
+// WithTable is a functional option that renders a YAML metadata as a table.
+func WithTable() Option {
+	return func(m *meta) {
+		m.Table = true
+	}
+}
+
+type meta struct {
+	Table bool
+}
+
+// Meta is a extension for the goldmark.
+var Meta = &meta{}
+
+// New returns a new Meta extension.
+func New(opts ...Option) goldmark.Extender {
+	e := &meta{}
+	for _, opt := range opts {
+		opt(e)
+	}
+	return e
+}
+
+func (e *meta) Extend(m goldmark.Markdown) {
+	m.Parser().AddOptions(
+		parser.WithBlockParsers(
+			util.Prioritized(NewParser(), 0),
+		),
+	)
+	if e.Table {
+		m.Parser().AddOptions(
+			parser.WithASTTransformers(
+				util.Prioritized(defaultASTTransformer, 0),
+			),
+		)
+	}
+}