markdown: add markdown rendering for doc/modules.md

Using github.com/yuin/goldmark for Markdown rendering. Rendering only
happens when ./content/static is generated. ./cmd/golangorg does not
need to render anything on request.

Updates golang/go#33637

Change-Id: I68c80b1ed6543f0985848c6e5a58a07da05c972d
Reviewed-on: https://go-review.googlesource.com/c/website/+/218517
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

content/static/gen.go

@@ -11,7 +11,10 @@ import (
 	"fmt"
 	"go/format"
 	"io/ioutil"
+	"strings"
 	"unicode"
+
+	"golang.org/x/website/markdown"
 )
 
 var files = []string{
@@ -68,21 +71,42 @@ var files = []string{
 	"style.css",
 }
 
+var markdownFiles = []string{
+	"doc/modules.md",
+}
+
 // Generate reads a set of files and returns a file buffer that declares
 // a map of string constants containing contents of the input files.
 func Generate() ([]byte, error) {
 	buf := new(bytes.Buffer)
 	fmt.Fprintf(buf, "%v\n\n%v\n\npackage static\n\n", license, warning)
 	fmt.Fprintf(buf, "var Files = map[string]string{\n")
+
 	for _, fn := range files {
 		b, err := ioutil.ReadFile(fn)
 		if err != nil {
-			return b, err
+			return nil, err
 		}
 		fmt.Fprintf(buf, "\t%q: ", fn)
 		appendQuote(buf, b)
 		fmt.Fprintf(buf, ",\n\n")
 	}
+
+	for _, fn := range markdownFiles {
+		src, err := ioutil.ReadFile(fn)
+		if err != nil {
+			return nil, err
+		}
+		gen, err := markdown.Render(src)
+		if err != nil {
+			return nil, fmt.Errorf("%s: %v", fn, err)
+		}
+		htmlName := strings.TrimSuffix(fn, ".md") + ".html"
+		fmt.Fprintf(buf, "\t%q: ", htmlName)
+		appendQuote(buf, gen)
+		fmt.Fprintf(buf, ",\n\n")
+	}
+
 	fmt.Fprintln(buf, "}")
 	return format.Source(buf.Bytes())
 }

go.mod

@@ -5,6 +5,7 @@ go 1.11
 require (
 	cloud.google.com/go v0.38.0
 	github.com/gomodule/redigo v2.0.0+incompatible
+	github.com/yuin/goldmark v1.1.22
 	go.opencensus.io v0.22.0 // indirect
 	golang.org/x/build v0.0.0-20191213161705-41fffb13b6ef
 	golang.org/x/net v0.0.0-20190620200207-3b0461eec859

go.sum

@@ -44,6 +44,8 @@ github.com/jellevandenhooff/dkim v0.0.0-20150330215556-f50fe3d243e1/go.mod h1:E0
 github.com/jstemmer/go-junit-report v0.0.0-20190106144839-af01ea7f8024/go.mod h1:6v2b51hI/fHJwM22ozAgKL4VKDeJcHhJFhtBdhmNjmU=
 github.com/kr/pty v1.1.3/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/tarm/serial v0.0.0-20180830185346-98f6abe2eb07/go.mod h1:kDXzergiv9cbyO7IOYJZWg1U88JhDg3PB6klq9Hg2pA=
+github.com/yuin/goldmark v1.1.22 h1:0e0f6Zee9SAQ5yOZGNMWaOxqVvcc/9/kUWu/Kl91Jk8=
+github.com/yuin/goldmark v1.1.22/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 go.opencensus.io v0.21.0/go.mod h1:mSImk1erAIZhrmZN+AvHh14ztQfjbGwt4TtuofqLduU=
 go.opencensus.io v0.22.0 h1:C9hSCOW830chIVkdja34wa6Ky+IzWllkUinR+BtRZd4=
 go.opencensus.io v0.22.0/go.mod h1:+kGneAE2xo2IficOXnaByMWTGM9T73dGwxeWcUqIpI8=

markdown/markdown.go

@@ -0,0 +1,35 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package markdown provides a wrapper for rendering Markdown. It is intended
+// to be used by x/website and x/blog so that we can use the same renderer
+// with the same settings.
+//
+// This package is not intended for general use, and its API is not guaranteed
+// to be stable.
+package markdown
+
+import (
+	"bytes"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/renderer/html"
+)
+
+// Render converts a limited and opinionated flavor of Markdown (compliant with
+// CommonMark 0.29) to HTML for the purposes of golang.org websites. This should
+// not be adjusted except for the needs of *.golang.org.
+//
+// The Markdown source may contain raw HTML and Go templates. Sanitization of
+// untrusted content is not performed: the caller is responsible for ensuring
+// that only trusted content is provided.
+func Render(src []byte) ([]byte, error) {
+	// html.WithUnsafe allows use of raw HTML, which we need for tables.
+	md := goldmark.New(goldmark.WithRendererOptions(html.WithUnsafe()))
+	var buf bytes.Buffer
+	if err := md.Convert(src, &buf); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}