Implement support for partial templates

config.go

@@ -1,8 +1,10 @@
 package main
 
 import (
+	"fmt"
 	"os"
 	"path"
+	"strings"
 	"text/template"
 
 	"github.com/BurntSushi/toml"
@@ -65,6 +67,17 @@ func (c *Config) LoadTemplates(path string) error {
 				URLs:  c.URLs,
 			}
 		},
+		"partial": func(name string, data interface{}) (interface{}, error) {
+			t, ok := c.Templates.FindPartial(name)
+			if !ok {
+				return "", fmt.Errorf("Error: partial %q not found", name)
+			}
+			var b strings.Builder
+			if err := t.Execute(&b, data); err != nil {
+				return "", err
+			}
+			return b.String(), nil
+		},
 	})
 	return c.Templates.Load(path)
 }

templates.go

@@ -67,3 +67,11 @@ func (t *Templates) FindTemplate(path string, tmpl string) (*template.Template,
 	// Failed to find template
 	return nil, false
 }
+
+// FindPartial returns the partial template of the given name.
+func (t *Templates) FindPartial(name string) (*template.Template, bool) {
+	if t, ok := t.tmpls[pathpkg.Join("/_partials", name)]; ok {
+		return t, true
+	}
+	return nil, false
+}