Prepare for Goldmark

This commmit prepares for the addition of Goldmark as the new Markdown renderer in Hugo.

This introduces a new `markup` package with some common interfaces and each implementation in its own package.

See #5963

2 files changed, 114 insertions, 0 deletions

diff --git a/markup/pandoc/convert.go b/markup/pandoc/convert.go
new file mode 100644
index 000000000..4deab0b46
--- /dev/null
+++ b/markup/pandoc/convert.go
@@ -0,0 +1,76 @@
+// Copyright 2019 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 pandoc converts content to HTML using Pandoc as an external helper.
+package pandoc
+
+import (
+	"os/exec"
+
+	"github.com/gohugoio/hugo/markup/internal"
+
+	"github.com/gohugoio/hugo/markup/converter"
+)
+
+// Provider is the package entry point.
+var Provider converter.NewProvider = provider{}
+
+type provider struct {
+}
+
+func (p provider) New(cfg converter.ProviderConfig) (converter.Provider, error) {
+	var n converter.NewConverter = func(ctx converter.DocumentContext) (converter.Converter, error) {
+		return &pandocConverter{
+			ctx: ctx,
+			cfg: cfg,
+		}, nil
+	}
+	return n, nil
+
+}
+
+type pandocConverter struct {
+	ctx converter.DocumentContext
+	cfg converter.ProviderConfig
+}
+
+func (c *pandocConverter) Convert(ctx converter.RenderContext) (converter.Result, error) {
+	return converter.Bytes(c.getPandocContent(ctx.Src, c.ctx)), nil
+}
+
+// getPandocContent calls pandoc as an external helper to convert pandoc markdown to HTML.
+func (c *pandocConverter) getPandocContent(src []byte, ctx converter.DocumentContext) []byte {
+	logger := c.cfg.Logger
+	path := getPandocExecPath()
+	if path == "" {
+		logger.ERROR.Println("pandoc not found in $PATH: Please install.\n",
+			"                 Leaving pandoc content unrendered.")
+		return src
+	}
+	args := []string{"--mathjax"}
+	return internal.ExternallyRenderContent(c.cfg, ctx, src, path, args)
+}
+
+func getPandocExecPath() string {
+	path, err := exec.LookPath("pandoc")
+	if err != nil {
+		return ""
+	}
+
+	return path
+}
+
+// Supports returns whether Pandoc is installed on this computer.
+func Supports() bool {
+	return getPandocExecPath() != ""
+}
diff --git a/markup/pandoc/convert_test.go b/markup/pandoc/convert_test.go
new file mode 100644
index 000000000..bd6ca19e6
--- /dev/null
+++ b/markup/pandoc/convert_test.go
@@ -0,0 +1,38 @@
+// Copyright 2019 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 pandoc
+
+import (
+	"testing"
+
+	"github.com/gohugoio/hugo/common/loggers"
+
+	"github.com/gohugoio/hugo/markup/converter"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestConvert(t *testing.T) {
+	if !Supports() {
+		t.Skip("pandoc not installed")
+	}
+	c := qt.New(t)
+	p, err := Provider.New(converter.ProviderConfig{Logger: loggers.NewErrorLogger()})
+	c.Assert(err, qt.IsNil)
+	conv, err := p.New(converter.DocumentContext{})
+	c.Assert(err, qt.IsNil)
+	b, err := conv.Convert(converter.RenderContext{Src: []byte("testContent")})
+	c.Assert(err, qt.IsNil)
+	c.Assert(string(b.Bytes()), qt.Equals, "<p>testContent</p>\n")
+}