Add resources.Copy

Implemented by most Resource objects, but not Page (for now).

Fixes #9313

5 files changed, 59 insertions, 4 deletions

diff --git a/resources/image.go b/resources/image.go
index f431784b4..3eda709d9 100644
--- a/resources/image.go
+++ b/resources/image.go
@@ -134,7 +134,7 @@ func (i *imageResource) getExif() *exif.ExifInfo {
 	return i.meta.Exif
 }
 
-// Cloneis for internal use.
+// Clone is for internal use.
 func (i *imageResource) Clone() resource.Resource {
 	gr := i.baseResource.Clone().(baseResource)
 	return &imageResource{
@@ -144,6 +144,15 @@ func (i *imageResource) Clone() resource.Resource {
 	}
 }
 
+func (i *imageResource) cloneTo(targetPath string) resource.Resource {
+	gr := i.baseResource.cloneTo(targetPath).(baseResource)
+	return &imageResource{
+		root:         i.root,
+		Image:        i.WithSpec(gr),
+		baseResource: gr,
+	}
+}
+
 func (i *imageResource) cloneWithUpdates(u *transformationUpdate) (baseResource, error) {
 	base, err := i.baseResource.cloneWithUpdates(u)
 	if err != nil {
diff --git a/resources/resource.go b/resources/resource.go
index ead483d65..e38090dbe 100644
--- a/resources/resource.go
+++ b/resources/resource.go
@@ -1,4 +1,4 @@
-// Copyright 2019 The Hugo Authors. All rights reserved.
+// Copyright 2022 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.
@@ -120,8 +120,19 @@ func (t transformerNotAvailable) Key() internal.ResourceTransformationKey {
 	return t.key
 }
 
+// resourceCopier is for internal use.
+type resourceCopier interface {
+	cloneTo(targetPath string) resource.Resource
+}
+
+// Copy copies r to the targetPath given.
+func Copy(r resource.Resource, targetPath string) resource.Resource {
+	return r.(resourceCopier).cloneTo(targetPath)
+}
+
 type baseResourceResource interface {
 	resource.Cloner
+	resourceCopier
 	resource.ContentProvider
 	resource.Resource
 	resource.Identifier
@@ -225,6 +236,20 @@ func (l *genericResource) Clone() resource.Resource {
 	return l.clone()
 }
 
+func (l *genericResource) cloneTo(targetPath string) resource.Resource {
+	c := l.clone()
+
+	targetPath = helpers.ToSlashTrimLeading(targetPath)
+	dir, file := path.Split(targetPath)
+
+	c.resourcePathDescriptor = &resourcePathDescriptor{
+		relTargetDirFile: dirFile{dir: dir, file: file},
+	}
+
+	return c
+
+}
+
 func (l *genericResource) Content() (any, error) {
 	if err := l.initContent(); err != nil {
 		return nil, err
diff --git a/resources/resource/resourcetypes.go b/resources/resource/resourcetypes.go
index e3251aabe..4ba95c170 100644
--- a/resources/resource/resourcetypes.go
+++ b/resources/resource/resourcetypes.go
@@ -26,8 +26,7 @@ var (
 	_ ResourceError        = (*resourceError)(nil)
 )
 
-// Cloner is an internal template and not meant for use in the templates. It
-// may change without notice.
+// Cloner is for internal use.
 type Cloner interface {
 	Clone() Resource
 }
diff --git a/resources/resource_factories/create/create.go b/resources/resource_factories/create/create.go
index 3827411a9..075d25736 100644
--- a/resources/resource_factories/create/create.go
+++ b/resources/resource_factories/create/create.go
@@ -51,6 +51,13 @@ func New(rs *resources.Spec) *Client {
 	}
 }
 
+// Copy copies r to the new targetPath.
+func (c *Client) Copy(r resource.Resource, targetPath string) (resource.Resource, error) {
+	return c.rs.ResourceCache.GetOrCreate(resources.ResourceCacheKey(targetPath), func() (resource.Resource, error) {
+		return resources.Copy(r, targetPath), nil
+	})
+}
+
 // Get creates a new Resource by opening the given filename in the assets filesystem.
 func (c *Client) Get(filename string) (resource.Resource, error) {
 	filename = filepath.Clean(filename)
diff --git a/resources/transform.go b/resources/transform.go
index a470c94da..bb1608cbd 100644
--- a/resources/transform.go
+++ b/resources/transform.go
@@ -42,6 +42,7 @@ import (
 
 var (
 	_ resource.ContentResource        = (*resourceAdapter)(nil)
+	_ resourceCopier                  = (*resourceAdapter)(nil)
 	_ resource.ReadSeekCloserResource = (*resourceAdapter)(nil)
 	_ resource.Resource               = (*resourceAdapter)(nil)
 	_ resource.Source                 = (*resourceAdapter)(nil)
@@ -175,6 +176,19 @@ func (r *resourceAdapter) Data() any {
 	return r.target.Data()
 }
 
+func (r resourceAdapter) cloneTo(targetPath string) resource.Resource {
+	newtTarget := r.target.cloneTo(targetPath)
+	newInner := &resourceAdapterInner{
+		spec:   r.spec,
+		target: newtTarget.(transformableResource),
+	}
+	if r.resourceAdapterInner.publishOnce != nil {
+		newInner.publishOnce = &publishOnce{}
+	}
+	r.resourceAdapterInner = newInner
+	return &r
+}
+
 func (r *resourceAdapter) Crop(spec string) (images.ImageResource, error) {
 	return r.getImageOps().Crop(spec)
 }
@@ -596,6 +610,7 @@ type transformableResource interface {
 	resource.ContentProvider
 	resource.Resource
 	resource.Identifier
+	resourceCopier
 }
 
 type transformationUpdate struct {