cache/filecache: Add a cache prune func

Fixes #5439

hugolib/prune_resources.go

@@ -1,4 +1,4 @@
-// Copyright 2017-present The Hugo Authors. All rights reserved.
+// Copyright 2018 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.
@@ -13,89 +13,7 @@
 
 package hugolib
 
-import (
-	"io"
-	"os"
-	"strings"
-
-	"github.com/gohugoio/hugo/helpers"
-
-	"github.com/spf13/afero"
-)
-
-// GC requires a build first.
+// GC requires a build first and must run on it's own. It is not thread safe.
 func (h *HugoSites) GC() (int, error) {
-	s := h.Sites[0]
-	assetsCacheFs := h.Deps.FileCaches.AssetsCache().Fs
-	imageCacheFs := h.Deps.FileCaches.ImageCache().Fs
-
-	isImageInUse := func(name string) bool {
-		for _, site := range h.Sites {
-			if site.ResourceSpec.IsInImageCache(name) {
-				return true
-			}
-		}
-
-		return false
-	}
-
-	isAssetInUse := func(name string) bool {
-		// These assets are stored in tuplets with an added extension to the key.
-		key := strings.TrimSuffix(name, helpers.Ext(name))
-		for _, site := range h.Sites {
-			if site.ResourceSpec.ResourceCache.Contains(key) {
-				return true
-			}
-		}
-
-		return false
-	}
-
-	walker := func(fs afero.Fs, dirname string, inUse func(filename string) bool) (int, error) {
-		counter := 0
-		err := afero.Walk(fs, dirname, func(path string, info os.FileInfo, err error) error {
-			if info == nil {
-				return nil
-			}
-
-			if info.IsDir() {
-				f, err := fs.Open(path)
-				if err != nil {
-					return nil
-				}
-				defer f.Close()
-				_, err = f.Readdirnames(1)
-				if err == io.EOF {
-					// Empty dir.
-					s.Fs.Source.Remove(path)
-				}
-
-				return nil
-			}
-
-			inUse := inUse(path)
-			if !inUse {
-				err := fs.Remove(path)
-				if err != nil && !os.IsNotExist(err) {
-					s.Log.ERROR.Printf("Failed to remove %q: %s", path, err)
-				} else {
-					counter++
-				}
-			}
-			return nil
-		})
-
-		return counter, err
-	}
-
-	imageCounter, err1 := walker(imageCacheFs, "", isImageInUse)
-	assetsCounter, err2 := walker(assetsCacheFs, "", isAssetInUse)
-	totalCount := imageCounter + assetsCounter
-
-	if err1 != nil {
-		return totalCount, err1
-	}
-
-	return totalCount, err2
-
+	return h.Deps.FileCaches.Prune()
 }