markup: Add blockquote render hooks

Closes #12590

markup/goldmark/blockquotes/blockquotes.go

@@ -0,0 +1,248 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package blockquotes
+
+import (
+	"regexp"
+	"strings"
+	"sync"
+
+	"github.com/gohugoio/hugo/common/herrors"
+	htext "github.com/gohugoio/hugo/common/text"
+	"github.com/gohugoio/hugo/common/types/hstring"
+	"github.com/gohugoio/hugo/markup/converter/hooks"
+	"github.com/gohugoio/hugo/markup/goldmark/internal/render"
+	"github.com/gohugoio/hugo/markup/internal/attributes"
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/renderer"
+	"github.com/yuin/goldmark/renderer/html"
+	"github.com/yuin/goldmark/util"
+)
+
+type (
+	blockquotesExtension struct{}
+	htmlRenderer         struct{}
+)
+
+func New() goldmark.Extender {
+	return &blockquotesExtension{}
+}
+
+func (e *blockquotesExtension) Extend(m goldmark.Markdown) {
+	m.Renderer().AddOptions(renderer.WithNodeRenderers(
+		util.Prioritized(newHTMLRenderer(), 100),
+	))
+}
+
+func newHTMLRenderer() renderer.NodeRenderer {
+	r := &htmlRenderer{}
+	return r
+}
+
+func (r *htmlRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	reg.Register(ast.KindBlockquote, r.renderBlockquote)
+}
+
+const (
+	typeRegular = "regular"
+	typeAlert   = "alert"
+)
+
+func (r *htmlRenderer) renderBlockquote(w util.BufWriter, src []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
+	ctx := w.(*render.Context)
+
+	n := node.(*ast.Blockquote)
+
+	if entering {
+		// Store the current pos so we can capture the rendered text.
+		ctx.PushPos(ctx.Buffer.Len())
+		return ast.WalkContinue, nil
+	}
+
+	pos := ctx.PopPos()
+	text := ctx.Buffer.Bytes()[pos:]
+	ctx.Buffer.Truncate(pos)
+
+	// Extract a source sample to use for position information.
+	nn := n.FirstChild()
+	var start, stop int
+	for i := 0; i < nn.Lines().Len() && i < 2; i++ {
+		line := nn.Lines().At(i)
+		if i == 0 {
+			start = line.Start
+		}
+		stop = line.Stop
+	}
+
+	// We do not mutate the source, so this is safe.
+	sourceRef := src[start:stop]
+
+	ordinal := ctx.GetAndIncrementOrdinal(ast.KindBlockquote)
+
+	texts := string(text)
+	typ := typeRegular
+	alertType := resolveGitHubAlert(texts)
+	if alertType != "" {
+		typ = typeAlert
+	}
+
+	renderer := ctx.RenderContext().GetRenderer(hooks.BlockquoteRendererType, typ)
+	if renderer == nil {
+		return r.renderBlockquoteDefault(w, n, texts)
+	}
+
+	if typ == typeAlert {
+		// Trim preamble: <p>[!NOTE]<br>\n but preserve leading paragraph.
+		// We could possibly complicate this by moving this to the parser, but
+		// keep it simple for now.
+		texts = "<p>" + texts[strings.Index(texts, "\n")+1:]
+	}
+
+	bqctx := &blockquoteContext{
+		page:             ctx.DocumentContext().Document,
+		pageInner:        r.getPageInner(ctx),
+		typ:              typ,
+		alertType:        alertType,
+		text:             hstring.RenderedString(texts),
+		sourceRef:        sourceRef,
+		ordinal:          ordinal,
+		AttributesHolder: attributes.New(n.Attributes(), attributes.AttributesOwnerGeneral),
+	}
+
+	bqctx.createPos = func() htext.Position {
+		if resolver, ok := renderer.(hooks.ElementPositionResolver); ok {
+			return resolver.ResolvePosition(bqctx)
+		}
+
+		return htext.Position{
+			Filename:     ctx.DocumentContext().Filename,
+			LineNumber:   1,
+			ColumnNumber: 1,
+		}
+	}
+
+	cr := renderer.(hooks.BlockquoteRenderer)
+
+	err := cr.RenderBlockquote(
+		ctx.RenderContext().Ctx,
+		w,
+		bqctx,
+	)
+	if err != nil {
+		return ast.WalkContinue, herrors.NewFileErrorFromPos(err, bqctx.createPos())
+	}
+
+	return ast.WalkContinue, nil
+}
+
+func (r *htmlRenderer) getPageInner(rctx *render.Context) any {
+	pid := rctx.PeekPid()
+	if pid > 0 {
+		if lookup := rctx.DocumentContext().DocumentLookup; lookup != nil {
+			if v := rctx.DocumentContext().DocumentLookup(pid); v != nil {
+				return v
+			}
+		}
+	}
+	return rctx.DocumentContext().Document
+}
+
+// Code borrowed from goldmark's html renderer.
+func (r *htmlRenderer) renderBlockquoteDefault(
+	w util.BufWriter, n ast.Node, text string,
+) (ast.WalkStatus, error) {
+	if n.Attributes() != nil {
+		_, _ = w.WriteString("<blockquote")
+		html.RenderAttributes(w, n, html.BlockquoteAttributeFilter)
+		_ = w.WriteByte('>')
+	} else {
+		_, _ = w.WriteString("<blockquote>\n")
+	}
+
+	_, _ = w.WriteString(text)
+
+	_, _ = w.WriteString("</blockquote>\n")
+	return ast.WalkContinue, nil
+}
+
+type blockquoteContext struct {
+	page      any
+	pageInner any
+	text      hstring.RenderedString
+	typ       string
+	sourceRef []byte
+	alertType string
+	ordinal   int
+
+	// This is only used in error situations and is expensive to create,
+	// so delay creation until needed.
+	pos       htext.Position
+	posInit   sync.Once
+	createPos func() htext.Position
+
+	*attributes.AttributesHolder
+}
+
+func (c *blockquoteContext) Type() string {
+	return c.typ
+}
+
+func (c *blockquoteContext) AlertType() string {
+	return c.alertType
+}
+
+func (c *blockquoteContext) Page() any {
+	return c.page
+}
+
+func (c *blockquoteContext) PageInner() any {
+	return c.pageInner
+}
+
+func (c *blockquoteContext) Text() hstring.RenderedString {
+	return c.text
+}
+
+func (c *blockquoteContext) Ordinal() int {
+	return c.ordinal
+}
+
+func (c *blockquoteContext) Position() htext.Position {
+	c.posInit.Do(func() {
+		c.pos = c.createPos()
+	})
+	return c.pos
+}
+
+func (c *blockquoteContext) PositionerSourceTarget() []byte {
+	return c.sourceRef
+}
+
+var _ hooks.PositionerSourceTargetProvider = (*blockquoteContext)(nil)
+
+// https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts
+// Five types:
+// [!NOTE], [!TIP], [!WARNING], [!IMPORTANT], [!CAUTION]
+var gitHubAlertRe = regexp.MustCompile(`^<p>\[!(NOTE|TIP|WARNING|IMPORTANT|CAUTION)\]`)
+
+// resolveGitHubAlert returns one of note, tip, warning, important or caution.
+// An empty string if no match.
+func resolveGitHubAlert(s string) string {
+	m := gitHubAlertRe.FindStringSubmatch(s)
+	if len(m) == 2 {
+		return strings.ToLower(m[1])
+	}
+	return ""
+}