--cache-from invalidates caches for ADD command

[zen0wu]

Description

Steps to reproduce the issue:

1. Use the following simple Dockerfile

FROM python:3.6.5

RUN echo "START"
RUN mkdir /test
ADD a /test
RUN echo "AHA"

2. Run docker build --cache-from shivawu/test-cache-from .
3. Run 2 again

Describe the results you received:

[ec2-user@ip-192-0-0-151 test]$ docker build --pull -t shivawu/test-cache-from:test6 --cache-from shivawu/test-cache-from:test5 .
Sending build context to Docker daemon  2.56 kB
Step 1/6 : FROM python:3.6.5
3.6.5: Pulling from library/python
Digest: sha256:ed978c29213ab3360766d2f42a898d5faa60e27294f142ba58c6c3617896a52b
Status: Image is up to date for python:3.6.5
 ---> efb6baa1169f
Step 2/6 : RUN apt-get update && apt-get install -y vim
 ---> Using cache
 ---> ea40cb37d9bf
Step 3/6 : RUN echo "START"
 ---> Using cache
 ---> 5f18a85fd606
Step 4/6 : RUN mkdir /test
 ---> Using cache
 ---> 1451f6ff4b55
Step 5/6 : ADD a /test
 ---> 5ca8fec6c97f
Removing intermediate container 8bd9a93a1edf
Step 6/6 : RUN echo "AHA"
 ---> Running in cd6a87a7c1c8
AHA
 ---> cd286d325aca
Removing intermediate container cd6a87a7c1c8
Successfully built cd286d325aca
[ec2-user@ip-192-0-0-151 test]$ docker build --pull -t shivawu/test-cache-from:test6 --cache-from shivawu/test-cache-from:test5 .
Sending build context to Docker daemon  2.56 kB
Step 1/6 : FROM python:3.6.5
3.6.5: Pulling from library/python
Digest: sha256:ed978c29213ab3360766d2f42a898d5faa60e27294f142ba58c6c3617896a52b
Status: Image is up to date for python:3.6.5
 ---> efb6baa1169f
Step 2/6 : RUN apt-get update && apt-get install -y vim
 ---> Using cache
 ---> ea40cb37d9bf
Step 3/6 : RUN echo "START"
 ---> Using cache
 ---> 5f18a85fd606
Step 4/6 : RUN mkdir /test
 ---> Using cache
 ---> 1451f6ff4b55
Step 5/6 : ADD a /test
 ---> 85441a2840a8
Removing intermediate container 3805300332bc
Step 6/6 : RUN echo "AHA"
 ---> Running in e0c8bbfed714
AHA
 ---> 6e496426a963
Removing intermediate container e0c8bbfed714
Successfully built 6e496426a963

Describe the results you expected:

As you can see, the two run of docker build diverge from step 5, all steps from 1-4 are using the cache, but when encountered an ADD instruction, it fails to use the cache.

Additional information you deem important (e.g. issue happens only occasionally):

Output of docker version:

Client:
 Version:	18.03.0-ce
 API version:	1.37
 Go version:	go1.9.4
 Git commit:	0520e24
 Built:	Wed Mar 21 23:06:22 2018
 OS/Arch:	darwin/amd64
 Experimental:	false
 Orchestrator:	swarm

Server:
 Engine:
  Version:	18.03.0-ce
  API version:	1.37 (minimum version 1.12)
  Go version:	go1.9.4
  Git commit:	0520e24
  Built:	Wed Mar 21 23:14:32 2018
  OS/Arch:	linux/amd64
  Experimental:	true

Output of docker info:

Containers: 0
 Running: 0
 Paused: 0
 Stopped: 0
Images: 44
Server Version: 18.03.0-ce
Storage Driver: overlay2
 Backing Filesystem: extfs
 Supports d_type: true
 Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host ipvlan macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: cfd04396dc68220d1cecbe686a6cc3aa5ce3667c
runc version: 4fc53a81fb7c994640722ac585fa9ca548971871
init version: 949e6fa
Security Options:
 seccomp
  Profile: default
Kernel Version: 4.9.87-linuxkit-aufs
Operating System: Docker for Mac
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 1.952GiB
Name: linuxkit-025000000001
ID: Z2LA:YT54:G4DX:G4LY:JAH2:5DVY:ZCUZ:F2GA:DXNX:BE6Z:IICC:ZC5X
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): true
 File Descriptors: 22
 Goroutines: 40
 System Time: 2018-04-03T05:26:33.970715485Z
 EventsListeners: 2
HTTP Proxy: docker.for.mac.http.internal:3128
HTTPS Proxy: docker.for.mac.http.internal:3129
Registry: https://index.docker.io/v1/
Labels:
Experimental: true
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

Additional environment details (AWS, VirtualBox, physical, etc.):

[arm64b]

I can't reproduce in my system, or your produce steps list above is not exactly match your actual operation.
First you need to tag the image you're building like this:
docker build -t shivawu/test-cache-from ., then you can test if the cache is OK with:
docker build --cache-from shivawu/test-cache-from -t shivawu/test-cache-from:test0 .