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

markup/converter/converter.go

@@ -0,0 +1,83 @@
+// 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 converter
+
+import (
+	"github.com/gohugoio/hugo/common/loggers"
+	"github.com/gohugoio/hugo/config"
+	"github.com/spf13/afero"
+)
+
+// ProviderConfig configures a new Provider.
+type ProviderConfig struct {
+	Cfg       config.Provider // Site config
+	ContentFs afero.Fs
+	Logger    *loggers.Logger
+	Highlight func(code, lang, optsStr string) (string, error)
+}
+
+// NewProvider creates converter providers.
+type NewProvider interface {
+	New(cfg ProviderConfig) (Provider, error)
+}
+
+// Provider creates converters.
+type Provider interface {
+	New(ctx DocumentContext) (Converter, error)
+}
+
+// NewConverter is an adapter that can be used as a ConverterProvider.
+type NewConverter func(ctx DocumentContext) (Converter, error)
+
+// New creates a new Converter for the given ctx.
+func (n NewConverter) New(ctx DocumentContext) (Converter, error) {
+	return n(ctx)
+}
+
+// Converter wraps the Convert method that converts some markup into
+// another format, e.g. Markdown to HTML.
+type Converter interface {
+	Convert(ctx RenderContext) (Result, error)
+}
+
+// Result represents the minimum returned from Convert.
+type Result interface {
+	Bytes() []byte
+}
+
+// DocumentInfo holds additional information provided by some converters.
+type DocumentInfo interface {
+	AnchorSuffix() string
+}
+
+// Bytes holds a byte slice and implements the Result interface.
+type Bytes []byte
+
+// Bytes returns itself
+func (b Bytes) Bytes() []byte {
+	return b
+}
+
+// DocumentContext holds contextual information about the document to convert.
+type DocumentContext struct {
+	DocumentID      string
+	DocumentName    string
+	ConfigOverrides map[string]interface{}
+}
+
+// RenderContext holds contextual information about the content to render.
+type RenderContext struct {
+	Src       []byte
+	RenderTOC bool
+}