Emulate github-pages plugin

config/config.go

@@ -145,7 +145,7 @@ func (c *Config) RequiresFrontMatter(rel string) bool {
 		return true
 	case !c.IsMarkdown(rel):
 		return true
-	case utils.StringContains(c.Include, rel):
+	case utils.StringArrayContains(c.Include, rel):
 		return false
 	case c.RequireFrontMatterExclude[strings.ToUpper(utils.TrimExt(filepath.Base(rel)))]:
 		return true

docs/plugins.md

@@ -24,6 +24,7 @@ The functionality of some plugins is built into the core program:
 | [jekyll-sitemap][jekyll-sitemap]                             | GitHub Pages  | ✓                     | file modified dates⁴                                                                                                                  |
 | [jekyll-titles-from-headings][jekyll-titles-from-headings]   | GitHub Pages  |                       |                                                                                                                                       |
 | [jemoji][jemoji]                                             | GitHub Pages  | ✓                     | image tag fallback                                                                                                                    |
+| [GitHub pages][github-pages]                                 | GitHub Pages  | ✓                     | The plugins that github-pages *includes* are in various stages of implementation, listed above                                        |
 
 ¹ (1) The code and internal APIs are too immature for this; and (2) the [natural way](https://golang.org/pkg/plugin/) of implementing this only works on Linux.
 
@@ -53,3 +54,4 @@ The [Official Plugins](https://jekyllrb.com/docs/plugins/#available-plugins) sec
 [jekyll-sitemap]: https://github.com/jekyll/jekyll-sitemap
 [jekyll-titles-from-headings]: https://github.com/benbalter/jekyll-titles-from-headings
 [jemoji]: https://github.com/jekyll/jemoji
+[github-pages]: https://github.com/github/pages-gem

plugins/github_pages.go

@@ -0,0 +1,38 @@
+package plugins
+
+import "github.com/osteele/gojekyll/utils"
+
+func init() {
+	register("github-pages", githubPagesPlugin{})
+}
+
+type githubPagesPlugin struct{ plugin }
+
+func (p githubPagesPlugin) ModifyPluginList(names []string) []string {
+	for _, name := range githubPagesPlugins {
+		if !utils.StringArrayContains(names, name) {
+			names = append(names, name)
+		}
+	}
+	return names
+}
+
+var githubPagesPlugins = []string{
+	"jekyll-avatar",
+	"jekyll-coffeescript",
+	"jekyll-default-layout",
+	"jekyll-feed",
+	"jekyll-gist",
+	"jekyll-github-metadata",
+	"jekyll-mentions",
+	"jekyll-optional-front-matter",
+	"jekyll-paginate",
+	"jekyll-readme-index",
+	"jekyll-redirect-from",
+	"jekyll-relative-links",
+	"jekyll-sass-converter",
+	"jekyll-seo-tag",
+	"jekyll-sitemap",
+	"jekyll-titles-from-headings",
+	"jemoji",
+}

plugins/plugins.go

@@ -21,6 +21,7 @@ import (
 type Plugin interface {
 	Initialize(Site) error
 	ConfigureTemplateEngine(*liquid.Engine) error
+	ModifyPluginList([]string) []string
 	ModifySiteDrop(Site, map[string]interface{}) error
 	PostRead(Site) error
 	PostRender([]byte) ([]byte, error)
@@ -42,16 +43,17 @@ func Lookup(name string) (Plugin, bool) {
 }
 
 // Install installs a registered plugin.
-func Install(names []string, site Site) {
+func Install(names []string, site Site) error {
 	for _, name := range names {
 		if p, found := directory[name]; found {
 			if err := p.Initialize(site); err != nil {
-				panic(err)
+				return err
 			}
 		} else {
 			fmt.Printf("warning: gojekyll does not emulate the %s plugin.\n", name)
 		}
 	}
+	return nil
 }
 
 // Names returns a sorted list of names of registered plugins.
@@ -71,6 +73,7 @@ type plugin struct{}
 
 func (p plugin) Initialize(Site) error                             { return nil }
 func (p plugin) ConfigureTemplateEngine(*liquid.Engine) error      { return nil }
+func (p plugin) ModifyPluginList(names []string) []string          { return names }
 func (p plugin) ModifySiteDrop(Site, map[string]interface{}) error { return nil }
 func (p plugin) PostRead(Site) error                               { return nil }
 func (p plugin) PostRender(b []byte) ([]byte, error)               { return b, nil }

site/plugins.go

@@ -0,0 +1,51 @@
+package site
+
+import (
+	"github.com/osteele/gojekyll/plugins"
+	"github.com/osteele/gojekyll/utils"
+)
+
+func (s *Site) installPlugins() error {
+	names := s.cfg.Plugins
+	installed := map[string]bool{}
+	// install plugins and call their ModifyPluginList lists
+	for {
+		pending := []string{}
+		for _, name := range names {
+			if !installed[name] {
+				pending = append(pending, name)
+			}
+		}
+		if len(pending) == 0 {
+			break
+		}
+		if err := plugins.Install(pending, s); err != nil {
+			return err
+		}
+		for _, name := range names {
+			if !installed[name] {
+				p, ok := plugins.Lookup(name)
+				if ok {
+					names = p.ModifyPluginList(names)
+				}
+			}
+		}
+		for _, name := range pending {
+			installed[name] = true
+		}
+	}
+	s.plugins = names
+	return nil
+}
+
+func (s *Site) runHooks(h func(plugins.Plugin) error) error {
+	for _, name := range s.plugins {
+		p, ok := plugins.Lookup(name)
+		if ok {
+			if err := h(p); err != nil {
+				return utils.WrapError(err, "running plugin")
+			}
+		}
+	}
+	return nil
+}

site/read.go

@@ -25,8 +25,10 @@ func FromDirectory(dir string, flags config.Flags) (*Site, error) {
 
 // Read loads the site data and files.
 func (s *Site) Read() error {
+	if err := s.installPlugins(); err != nil {
+		return utils.WrapError(err, "initializing plugins")
+	}
 	s.Routes = make(map[string]pages.Document)
-	plugins.Install(s.cfg.Plugins, s)
 	if err := s.findTheme(); err != nil {
 		return utils.WrapError(err, "finding theme")
 	}

site/site.go

@@ -22,6 +22,7 @@ type Site struct {
 	cfg      config.Config
 	data     map[string]interface{} // from _data files
 	flags    config.Flags           // command-line flags, override config files
+	plugins  []string               // initially cfg.Plugins, but plugins can modify this this
 	themeDir string                 // absolute path to theme directory
 
 	docs               []pages.Document // all documents, whether or not they are output
@@ -88,18 +89,6 @@ func (s *Site) Config() *config.Config {
 	return &s.cfg
 }
 
-func (s *Site) runHooks(h func(plugins.Plugin) error) error {
-	for _, name := range s.cfg.Plugins {
-		p, ok := plugins.Lookup(name)
-		if ok {
-			if err := h(p); err != nil {
-				return utils.WrapError(err, "running plugin")
-			}
-		}
-	}
-	return nil
-}
-
 // Site is in the pages.RenderingContext interface.
 func (s *Site) Site() interface{} {
 	return s

utils/strings.go

@@ -58,8 +58,8 @@ func StringArrayToMap(a []string) map[string]bool {
 	return m
 }
 
-// StringContains returns a bool indicating whether the array contains the string.
-func StringContains(a []string, s string) bool {
+// StringArrayContains returns a bool indicating whether the array contains the string.
+func StringArrayContains(a []string, s string) bool {
 	for _, item := range a {
 		if item == s {
 			return true