Add Markdown diagrams and render hooks for code blocks

You can now create custom hook templates for code blocks, either one for all (`render-codeblock.html`) or for a given code language (e.g. `render-codeblock-go.html`).

We also used this new hook to add support for diagrams in Hugo:

* Goat (Go ASCII Tool) is built-in and enabled by default; just create a fenced code block with the language `goat` and start draw your Ascii diagrams.
* Another popular alternative for diagrams in Markdown, Mermaid (supported by GitHub), can also be implemented with a simple template. See the Hugo documentation for more information.

Updates #7765
Closes #9538
Fixes #9553
Fixes #8520
Fixes #6702
Fixes #9558

2 files changed, 234 insertions, 43 deletions

diff --git a/markup/highlight/config.go b/markup/highlight/config.go
index 1dc1e28e2..86ac02c3d 100644
--- a/markup/highlight/config.go
+++ b/markup/highlight/config.go
@@ -20,6 +20,7 @@ import (
 	"strings"
 
 	"github.com/alecthomas/chroma/formatters/html"
+	"github.com/spf13/cast"
 
 	"github.com/gohugoio/hugo/config"
 
@@ -46,6 +47,9 @@ type Config struct {
 	// Use inline CSS styles.
 	NoClasses bool
 
+	// No highlighting.
+	NoHl bool
+
 	// When set, line numbers will be printed.
 	LineNos            bool
 	LineNumbersInTable bool
@@ -60,6 +64,9 @@ type Config struct {
 	// A space separated list of line numbers, e.g. “3-8 10-20”.
 	Hl_Lines string
 
+	// A parsed and ready to use list of line ranges.
+	HL_lines_parsed [][2]int
+
 	// TabWidth sets the number of characters for a tab. Defaults to 4.
 	TabWidth int
 
@@ -80,9 +87,19 @@ func (cfg Config) ToHTMLOptions() []html.Option {
 		html.LinkableLineNumbers(cfg.AnchorLineNos, lineAnchors),
 	}
 
-	if cfg.Hl_Lines != "" {
-		ranges, err := hlLinesToRanges(cfg.LineNoStart, cfg.Hl_Lines)
-		if err == nil {
+	if cfg.Hl_Lines != "" || cfg.HL_lines_parsed != nil {
+		var ranges [][2]int
+		if cfg.HL_lines_parsed != nil {
+			ranges = cfg.HL_lines_parsed
+		} else {
+			var err error
+			ranges, err = hlLinesToRanges(cfg.LineNoStart, cfg.Hl_Lines)
+			if err != nil {
+				ranges = nil
+			}
+		}
+
+		if ranges != nil {
 			options = append(options, html.HighlightLines(ranges))
 		}
 	}
@@ -90,14 +107,32 @@ func (cfg Config) ToHTMLOptions() []html.Option {
 	return options
 }
 
+func applyOptions(opts interface{}, cfg *Config) error {
+	if opts == nil {
+		return nil
+	}
+	switch vv := opts.(type) {
+	case map[string]interface{}:
+		return applyOptionsFromMap(vv, cfg)
+	case string:
+		return applyOptionsFromString(vv, cfg)
+	}
+	return nil
+}
+
 func applyOptionsFromString(opts string, cfg *Config) error {
-	optsm, err := parseOptions(opts)
+	optsm, err := parseHightlightOptions(opts)
 	if err != nil {
 		return err
 	}
 	return mapstructure.WeakDecode(optsm, cfg)
 }
 
+func applyOptionsFromMap(optsm map[string]interface{}, cfg *Config) error {
+	normalizeHighlightOptions(optsm)
+	return mapstructure.WeakDecode(optsm, cfg)
+}
+
 // ApplyLegacyConfig applies legacy config from back when we had
 // Pygments.
 func ApplyLegacyConfig(cfg config.Provider, conf *Config) error {
@@ -128,7 +163,7 @@ func ApplyLegacyConfig(cfg config.Provider, conf *Config) error {
 	return nil
 }
 
-func parseOptions(in string) (map[string]interface{}, error) {
+func parseHightlightOptions(in string) (map[string]interface{}, error) {
 	in = strings.Trim(in, " ")
 	opts := make(map[string]interface{})
 
@@ -142,19 +177,57 @@ func parseOptions(in string) (map[string]interface{}, error) {
 		if len(keyVal) != 2 {
 			return opts, fmt.Errorf("invalid Highlight option: %s", key)
 		}
-		if key == "linenos" {
-			opts[key] = keyVal[1] != "false"
-			if keyVal[1] == "table" || keyVal[1] == "inline" {
-				opts["lineNumbersInTable"] = keyVal[1] == "table"
-			}
-		} else {
-			opts[key] = keyVal[1]
-		}
+		opts[key] = keyVal[1]
+
 	}
 
+	normalizeHighlightOptions(opts)
+
 	return opts, nil
 }
 
+func normalizeHighlightOptions(m map[string]interface{}) {
+	if m == nil {
+		return
+	}
+
+	const (
+		lineNosKey    = "linenos"
+		hlLinesKey    = "hl_lines"
+		linosStartKey = "linenostart"
+		noHlKey       = "nohl"
+	)
+
+	baseLineNumber := 1
+	if v, ok := m[linosStartKey]; ok {
+		baseLineNumber = cast.ToInt(v)
+	}
+
+	for k, v := range m {
+		switch k {
+		case noHlKey:
+			m[noHlKey] = cast.ToBool(v)
+		case lineNosKey:
+			if v == "table" || v == "inline" {
+				m["lineNumbersInTable"] = v == "table"
+			}
+			if vs, ok := v.(string); ok {
+				m[k] = vs != "false"
+			}
+
+		case hlLinesKey:
+			if hlRanges, ok := v.([][2]int); ok {
+				for i := range hlRanges {
+					hlRanges[i][0] += baseLineNumber
+					hlRanges[i][1] += baseLineNumber
+				}
+				delete(m, k)
+				m[k+"_parsed"] = hlRanges
+			}
+		}
+	}
+}
+
 // startLine compensates for https://github.com/alecthomas/chroma/issues/30
 func hlLinesToRanges(startLine int, s string) ([][2]int, error) {
 	var ranges [][2]int
diff --git a/markup/highlight/highlight.go b/markup/highlight/highlight.go
index 319426241..e9cbeb3c9 100644
--- a/markup/highlight/highlight.go
+++ b/markup/highlight/highlight.go
@@ -16,47 +16,155 @@ package highlight
 import (
 	"fmt"
 	gohtml "html"
+	"html/template"
 	"io"
+	"strconv"
 	"strings"
 
 	"github.com/alecthomas/chroma"
 	"github.com/alecthomas/chroma/formatters/html"
 	"github.com/alecthomas/chroma/lexers"
 	"github.com/alecthomas/chroma/styles"
-	hl "github.com/yuin/goldmark-highlighting"
+	"github.com/gohugoio/hugo/common/hugio"
+	"github.com/gohugoio/hugo/identity"
+	"github.com/gohugoio/hugo/markup/converter/hooks"
+	"github.com/gohugoio/hugo/markup/internal/attributes"
 )
 
+// Markdown attributes used by the Chroma hightlighter.
+var chromaHightlightProcessingAttributes = map[string]bool{
+	"anchorLineNos":      true,
+	"guessSyntax":        true,
+	"hl_Lines":           true,
+	"lineAnchors":        true,
+	"lineNos":            true,
+	"lineNoStart":        true,
+	"lineNumbersInTable": true,
+	"noClasses":          true,
+	"style":              true,
+	"tabWidth":           true,
+}
+
+func init() {
+	for k, v := range chromaHightlightProcessingAttributes {
+		chromaHightlightProcessingAttributes[strings.ToLower(k)] = v
+	}
+}
+
 func New(cfg Config) Highlighter {
-	return Highlighter{
+	return chromaHighlighter{
 		cfg: cfg,
 	}
 }
 
-type Highlighter struct {
+type Highlighter interface {
+	Highlight(code, lang string, opts interface{}) (string, error)
+	HighlightCodeBlock(ctx hooks.CodeblockContext, opts interface{}) (HightlightResult, error)
+	hooks.CodeBlockRenderer
+}
+
+type chromaHighlighter struct {
 	cfg Config
 }
 
-func (h Highlighter) Highlight(code, lang, optsStr string) (string, error) {
-	if optsStr == "" {
-		return highlight(code, lang, h.cfg)
+func (h chromaHighlighter) Highlight(code, lang string, opts interface{}) (string, error) {
+	cfg := h.cfg
+	if err := applyOptions(opts, &cfg); err != nil {
+		return "", err
 	}
+	var b strings.Builder
 
-	cfg := h.cfg
-	if err := applyOptionsFromString(optsStr, &cfg); err != nil {
+	if err := highlight(&b, code, lang, nil, cfg); err != nil {
 		return "", err
 	}
 
-	return highlight(code, lang, cfg)
+	return b.String(), nil
 }
 
-func highlight(code, lang string, cfg Config) (string, error) {
-	w := &strings.Builder{}
+func (h chromaHighlighter) HighlightCodeBlock(ctx hooks.CodeblockContext, opts interface{}) (HightlightResult, error) {
+	cfg := h.cfg
+
+	var b strings.Builder
+
+	attributes := ctx.(hooks.AttributesOptionsSliceProvider).AttributesSlice()
+	options := ctx.Options()
+
+	if err := applyOptionsFromMap(options, &cfg); err != nil {
+		return HightlightResult{}, err
+	}
+
+	// Apply these last so the user can override them.
+	if err := applyOptions(opts, &cfg); err != nil {
+		return HightlightResult{}, err
+	}
+
+	err := highlight(&b, ctx.Code(), ctx.Lang(), attributes, cfg)
+	if err != nil {
+		return HightlightResult{}, err
+	}
+
+	return HightlightResult{
+		Body: template.HTML(b.String()),
+	}, nil
+}
+
+func (h chromaHighlighter) RenderCodeblock(w hugio.FlexiWriter, ctx hooks.CodeblockContext) error {
+	cfg := h.cfg
+	attributes := ctx.(hooks.AttributesOptionsSliceProvider).AttributesSlice()
+
+	if err := applyOptionsFromMap(ctx.Options(), &cfg); err != nil {
+		return err
+	}
+
+	return highlight(w, ctx.Code(), ctx.Lang(), attributes, cfg)
+}
+
+var id = identity.NewPathIdentity("chroma", "highlight")
+
+func (h chromaHighlighter) GetIdentity() identity.Identity {
+	return id
+}
+
+type HightlightResult struct {
+	Body template.HTML
+}
+
+func (h HightlightResult) Highlighted() template.HTML {
+	return h.Body
+}
+
+func (h chromaHighlighter) toHighlightOptionsAttributes(ctx hooks.CodeblockContext) (map[string]interface{}, map[string]interface{}) {
+	attributes := ctx.Attributes()
+	if attributes == nil || len(attributes) == 0 {
+		return nil, nil
+	}
+
+	options := make(map[string]interface{})
+	attrs := make(map[string]interface{})
+
+	for k, v := range attributes {
+		klow := strings.ToLower(k)
+		if chromaHightlightProcessingAttributes[klow] {
+			options[klow] = v
+		} else {
+			attrs[k] = v
+		}
+	}
+	const lineanchorsKey = "lineanchors"
+	if _, found := options[lineanchorsKey]; !found {
+		// Set it to the ordinal.
+		options[lineanchorsKey] = strconv.Itoa(ctx.Ordinal())
+	}
+	return options, attrs
+}
+
+func highlight(w hugio.FlexiWriter, code, lang string, attributes []attributes.Attribute, cfg Config) error {
 	var lexer chroma.Lexer
 	if lang != "" {
 		lexer = lexers.Get(lang)
 	}
 
-	if lexer == nil && cfg.GuessSyntax {
+	if lexer == nil && (cfg.GuessSyntax && !cfg.NoHl) {
 		lexer = lexers.Analyse(code)
 		if lexer == nil {
 			lexer = lexers.Fallback
@@ -69,7 +177,7 @@ func highlight(code, lang string, cfg Config) (string, error) {
 		fmt.Fprint(w, wrapper.Start(true, ""))
 		fmt.Fprint(w, gohtml.EscapeString(code))
 		fmt.Fprint(w, wrapper.End(true))
-		return w.String(), nil
+		return nil
 	}
 
 	style := styles.Get(cfg.Style)
@@ -80,7 +188,7 @@ func highlight(code, lang string, cfg Config) (string, error) {
 
 	iterator, err := lexer.Tokenise(nil, code)
 	if err != nil {
-		return "", err
+		return err
 	}
 
 	options := cfg.ToHTMLOptions()
@@ -88,25 +196,13 @@ func highlight(code, lang string, cfg Config) (string, error) {
 
 	formatter := html.New(options...)
 
-	fmt.Fprint(w, `<div class="highlight">`)
+	writeDivStart(w, attributes)
 	if err := formatter.Format(w, style, iterator); err != nil {
-		return "", err
+		return err
 	}
-	fmt.Fprint(w, `</div>`)
-
-	return w.String(), nil
-}
+	writeDivEnd(w)
 
-func GetCodeBlockOptions() func(ctx hl.CodeBlockContext) []html.Option {
-	return func(ctx hl.CodeBlockContext) []html.Option {
-		var language string
-		if l, ok := ctx.Language(); ok {
-			language = string(l)
-		}
-		return []html.Option{
-			getHtmlPreWrapper(language),
-		}
-	}
+	return nil
 }
 
 func getPreWrapper(language string) preWrapper {
@@ -150,3 +246,25 @@ func (p preWrapper) End(code bool) string {
 func WritePreEnd(w io.Writer) {
 	fmt.Fprint(w, preEnd)
 }
+
+func writeDivStart(w hugio.FlexiWriter, attrs []attributes.Attribute) {
+	w.WriteString(`<div class="highlight`)
+	if attrs != nil {
+		for _, attr := range attrs {
+			if attr.Name == "class" {
+				w.WriteString(" " + attr.ValueString())
+				break
+			}
+		}
+		_, _ = w.WriteString("\"")
+		attributes.RenderAttributes(w, true, attrs...)
+	} else {
+		_, _ = w.WriteString("\"")
+	}
+
+	w.WriteString(">")
+}
+
+func writeDivEnd(w hugio.FlexiWriter) {
+	w.WriteString("</div>")
+}