Add a plugin emulation mechanism

config/config.go

@@ -23,6 +23,9 @@ type Config struct {
 	Exclude     []string
 	MarkdownExt string `yaml:"markdown_ext"`
 
+	// Plugins
+	Plugins []string `yaml:"gems"` // TODO this differs from the Jekyll docs
+
 	// Serving
 	AbsoluteURL string `yaml:"url"`
 	BaseURL     string
@@ -78,6 +81,7 @@ func (c *Config) GetFrontMatterDefaults(relpath, typename string) (m templates.V
 }
 
 // From https://jekyllrb.com/docs/configuration/#default-configuration
+// The following includes only those keys that are currently implemented.
 const defaultSiteConfig = `
 # Where things are
 source:       .
@@ -97,6 +101,9 @@ encoding:             "utf-8"
 markdown_ext:         "markdown,mkdown,mkdn,mkd,md"
 strict_front_matter: false
 
+# Plugins
+plugins:   []
+
 # Outputting
 permalink:     date
 paginate_path: /page:num

liquid/engine.go

@@ -4,12 +4,14 @@ import (
 	"io"
 
 	"github.com/osteele/liquid"
+	"github.com/osteele/liquid/chunks"
 )
 
 // Engine is a configured liquid engine.
 type Engine interface {
 	Parse([]byte) (liquid.Template, error)
 	ParseAndRender([]byte, map[string]interface{}) ([]byte, error)
+	DefineTag(string, func(string) (func(io.Writer, chunks.Context) error, error))
 }
 
 // Wrapper is a wrapper around the Liquid engine.
@@ -35,6 +37,11 @@ func NewEngine() *Wrapper {
 	return e
 }
 
+// DefineTag is in the Engine interface.
+func (e *Wrapper) DefineTag(name string, f func(string) (func(io.Writer, chunks.Context) error, error)) {
+	e.engine.DefineTag(name, f)
+}
+
 // LinkTagHandler sets the link tag handler.
 func (e *Wrapper) LinkTagHandler(h LinkTagHandler) {
 	e.linkHandler = h

pipelines/pipeline.go

@@ -30,7 +30,6 @@ type Pipeline struct {
 // PipelineOptions configures a pipeline.
 type PipelineOptions struct {
 	SourceDir             string
-	AbsoluteURL, BaseURL  string
 	RelativeFilenameToURL liquid.LinkTagHandler
 }
 
@@ -44,6 +43,11 @@ func NewPipeline(c config.Config, options PipelineOptions) (*Pipeline, error) {
 	return &p, nil
 }
 
+// Engine returns the Liquid engine.
+func (p *Pipeline) TemplateEngine() liquid.Engine {
+	return p.liquidEngine
+}
+
 // OutputExt returns the output extension.
 func (p *Pipeline) OutputExt(pathname string) string {
 	return p.config.OutputExt(pathname)
@@ -108,9 +112,9 @@ func (p *Pipeline) makeLiquidEngine() liquid.Engine {
 		_, err = w.Write(text)
 		return err
 	}
+	engine.AbsoluteURL = p.config.AbsoluteURL
+	engine.BaseURL = p.config.BaseURL
 	engine.IncludeHandler(includeHandler)
 	engine.LinkTagHandler(p.RelativeFilenameToURL)
-	engine.AbsoluteURL = p.AbsoluteURL
-	engine.BaseURL = p.BaseURL
 	return engine
 }

plugins/plugins.go

@@ -0,0 +1,74 @@
+package plugins
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/osteele/gojekyll/liquid"
+	"github.com/osteele/liquid/chunks"
+)
+
+type PluginContext interface {
+	TemplateEngine() liquid.Engine
+}
+
+func Install(name string, ctx PluginContext) bool {
+	p, found := plugins[name]
+	if p != nil {
+		if err := p(ctx); err != nil {
+			panic(err)
+		}
+	}
+	return found
+}
+
+var plugins = map[string]func(PluginContext) error{}
+
+func registerPlugin(name string, fn func(PluginContext) error) {
+	plugins[name] = fn
+}
+
+func warnUnimplemented(name string) {
+	fmt.Printf("warning: gojekyll does not emulate the %s plugin. Some tags have been stubbed to prevent errors.\n", name)
+}
+
+func emptyTag(lexer string) (func(io.Writer, chunks.Context) error, error) {
+	return func(w io.Writer, _ chunks.Context) error { return nil }, nil
+}
+
+func init() {
+	registerPlugin("jekyll-avatar", func(ctx PluginContext) error {
+		warnUnimplemented("jekyll-avatar")
+		ctx.TemplateEngine().DefineTag("avatar", avatarTag)
+		return nil
+	})
+
+	registerPlugin("jekyll-feed", func(ctx PluginContext) error {
+		warnUnimplemented("jekyll-feed")
+		ctx.TemplateEngine().DefineTag("feed_meta", emptyTag)
+		return nil
+	})
+
+	registerPlugin("jekyll-seo-tag", func(ctx PluginContext) error {
+		warnUnimplemented("jekyll-seo-tag")
+		ctx.TemplateEngine().DefineTag("seo", emptyTag)
+		return nil
+	})
+
+	// registerPlugin("jekyll-sitemap")
+	// registerPlugin("jemoji")
+}
+
+const avatarTemplate = `<img class="avatar avatar-small" src="https://avatars3.githubusercontent.com/{username}?v=3&amp;s=40" alt="{username}" srcset="https://avatars3.githubusercontent.com/{username}?v=3&amp;s=40 1x, https://avatars3.githubusercontent.com/{username}?v=3&amp;s=80 2x, https://avatars3.githubusercontent.com/{username}?v=3&amp;s=120 3x, https://avatars3.githubusercontent.com/{username}?v=3&amp;s=160 4x" width="40" height="40" />`
+
+func avatarTag(filename string) (func(io.Writer, chunks.Context) error, error) {
+	username := "osteele" // TODO replace with real name
+	size := 40
+	return func(w io.Writer, _ chunks.Context) error {
+		s := strings.Replace(avatarTemplate, "40", fmt.Sprintf("%s", size), -1)
+		s = strings.Replace(s, "{username}", username, -1)
+		_, err := w.Write([]byte(s))
+		return err
+	}, nil
+}

sites/site.go

@@ -10,8 +10,10 @@ import (
 	"github.com/osteele/gojekyll/collections"
 	"github.com/osteele/gojekyll/config"
 	"github.com/osteele/gojekyll/helpers"
+	"github.com/osteele/gojekyll/liquid"
 	"github.com/osteele/gojekyll/pages"
 	"github.com/osteele/gojekyll/pipelines"
+	"github.com/osteele/gojekyll/plugins"
 	"github.com/osteele/gojekyll/templates"
 )
 
@@ -27,7 +29,7 @@ type Site struct {
 
 	config           config.Config
 	data             map[string]interface{}
-	pipeline         pipelines.PipelineInterface
+	pipeline         *pipelines.Pipeline
 	pages            []pages.Document // all pages, output or not
 	preparedToRender bool
 	siteVariables    templates.VariableMap
@@ -128,15 +130,26 @@ func (s *Site) RenderingPipeline() pipelines.PipelineInterface {
 	return s.pipeline
 }
 
+type pluginContext struct {
+	engine liquid.Engine
+}
+
+// Engine is in the PluginContext interface.
+func (c pluginContext) TemplateEngine() liquid.Engine { return c.engine }
+
 // initializeRenderingPipeline initializes the rendering pipeline
 func (s *Site) initializeRenderingPipeline() (err error) {
 	options := pipelines.PipelineOptions{
 		SourceDir:             s.Source,
-		AbsoluteURL:           s.config.AbsoluteURL,
-		BaseURL:               s.config.BaseURL,
 		RelativeFilenameToURL: s.RelativeFilenameToURL,
 	}
 	s.pipeline, err = pipelines.NewPipeline(s.config, options)
+	ctx := pluginContext{s.pipeline.TemplateEngine()}
+	for _, name := range s.config.Plugins {
+		if !plugins.Install(name, ctx) {
+			fmt.Printf("warning: gojekyll does not emulate the %s plugin.\n", name)
+		}
+	}
 	return
 }