Add a consolidated file cache

This commits reworks how file caching is performed in Hugo. Now there is only one way, and it can be configured.

This is the default configuration:

```toml
[caches]
[caches.getjson]
dir = ":cacheDir"
maxAge = -1
[caches.getcsv]
dir = ":cacheDir"
maxAge = -1
[caches.images]
dir = ":resourceDir/_gen"
maxAge = -1
[caches.assets]
dir = ":resourceDir/_gen"
maxAge = -1
```

You can override any of these cache setting in your own `config.toml`.

The placeholders explained:

`:cacheDir`: This is the value of the `cacheDir` config option if set (can also be set via OS env variable `HUGO_CACHEDIR`). It will fall back to `/opt/build/cache/hugo_cache/` on Netlify, or a `hugo_cache` directory below the OS temp dir for the others.
`:resourceDir`: This is the value of the `resourceDir` config option.

`maxAge` is the time in seconds before a cache entry will be evicted, -1 means forever and 0 effectively turns that particular cache off.

This means that if you run your builds on Netlify, all caches configured with `:cacheDir` will be saved and restored on the next build. For other CI vendors, please read their documentation. For an CircleCI example, see https://github.com/bep/hugo-sass-test/blob/6c3960a8f4b90e8938228688bc49bdcdd6b2d99e/.circleci/config.yml

Fixes #5404

1 files changed, 11 insertions, 15 deletions

diff --git a/resource/resource.go b/resource/resource.go
index be3ebdb8b..350519913 100644
--- a/resource/resource.go
+++ b/resource/resource.go
@@ -28,6 +28,7 @@ import (
 	"github.com/gohugoio/hugo/tpl"
 	"github.com/pkg/errors"
 
+	"github.com/gohugoio/hugo/cache/filecache"
 	"github.com/gohugoio/hugo/common/collections"
 	"github.com/gohugoio/hugo/common/hugio"
 	"github.com/gohugoio/hugo/common/loggers"
@@ -280,12 +281,15 @@ type Spec struct {
 
 	imageCache    *imageCache
 	ResourceCache *ResourceCache
-
-	GenImagePath  string
-	GenAssetsPath string
+	FileCaches    filecache.Caches
 }
 
-func NewSpec(s *helpers.PathSpec, logger *loggers.Logger, outputFormats output.Formats, mimeTypes media.Types) (*Spec, error) {
+func NewSpec(
+	s *helpers.PathSpec,
+	fileCaches filecache.Caches,
+	logger *loggers.Logger,
+	outputFormats output.Formats,
+	mimeTypes media.Types) (*Spec, error) {
 
 	imaging, err := decodeImaging(s.Cfg.GetStringMap("imaging"))
 	if err != nil {
@@ -296,24 +300,16 @@ func NewSpec(s *helpers.PathSpec, logger *loggers.Logger, outputFormats output.F
 		logger = loggers.NewErrorLogger()
 	}
 
-	genImagePath := filepath.FromSlash("_gen/images")
-	// The transformed assets (CSS etc.)
-	genAssetsPath := filepath.FromSlash("_gen/assets")
-
 	rs := &Spec{PathSpec: s,
 		Logger:        logger,
-		GenImagePath:  genImagePath,
-		GenAssetsPath: genAssetsPath,
 		imaging:       &imaging,
 		MediaTypes:    mimeTypes,
 		OutputFormats: outputFormats,
+		FileCaches:    fileCaches,
 		imageCache: newImageCache(
+			fileCaches.ImageCache(),
+
 			s,
-			// We're going to write a cache pruning routine later, so make it extremely
-			// unlikely that the user shoots him or herself in the foot
-			// and this is set to a value that represents data he/she
-			// cares about. This should be set in stone once released.
-			genImagePath,
 		)}
 
 	rs.ResourceCache = newResourceCache(rs)