[bug] Build args are not resolved over multi-stage build

[gabyx]

Description

ARG commands evaluate to different things in multi-stage builds on macOS (Docker Desktop 20.10.13) and Linux (20.10.14).

Steps to reproduce the issue: 1.

FROM alpine:latest as base
ARG NAME="1234"
RUN echo "base:: $NAME"  
FROM base AS base-dev
ARG NAME
RUN echo "dev:: $NAME"  
FROM base-dev as base-custom
ARG NAME
RUN echo "custom::" $NAME

2. docker build --progress=plain .
3. Check output of custom::

Describe the results you received:

On Docker Desktop on macOS 20.10.13:

Step 9/9 : RUN echo "custom::" $NAME
 ---> Running in 1c484bcc731d
custom:: 1234

On Linux 20.10.14:

Step 9/9 : RUN echo "custom::" $NAME
 ---> Running in 1c484bcc731d
custom:: 

Describe the results you expected:

On Linux the output should be also

custom:: 1234

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

Output of docker version:

Docker version 20.10.14, build a224086 (LINUX)

Docker version 20.10.13, build a224086 (macOS)

Output of docker info:

Linux:

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  app: Docker App (Docker Inc., v0.9.1-beta3)
  buildx: Docker Buildx (Docker Inc., v0.8.1-docker)
  scan: Docker Scan (Docker Inc., v0.17.0)

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 76
 Server Version: 20.10.14
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 3df54a852345ae127d1fa3092b95168e4a88e2f8
 runc version: v1.0.3-0-gf46b6ba
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: default
 Kernel Version: 5.4.0-107-generic
 Operating System: Ubuntu 20.04.4 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 32
 Total Memory: 62.79GiB
 Name: gabyx-linux
 ID: T4P2:2KQP:6FOQ:YQKN:JXOK:XXD4:XPRY:IA4S:4QOP:B2MQ:XJUI:AFJR
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Username: gabyxgabyx
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No swap limit support

macOS:

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc., v0.8.1)
  compose: Docker Compose (Docker Inc., v2.3.3)
  regctl: Manage docker registries (regclient, 0.1)
  scan: Docker Scan (Docker Inc., v0.17.0)

Server:
 Containers: 2
  Running: 1
  Paused: 0
  Stopped: 1
 Images: 25
 Server Version: 20.10.13
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 2a1d4dbdb2a1030dc5b01e96fb110a9d9f150ecc
 runc version: v1.0.3-0-gf46b6ba
 init version: de40ad0
 Security Options:
  seccomp
   Profile: default
  cgroupns
 Kernel Version: 5.10.104-linuxkit
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 8
 Total Memory: 9.73GiB
 Name: docker-desktop
 ID: REL6:ZZ3C:NB2L:Y7Q4:VMEY:BNLB:56PT:4S6U:62QD:Z4HU:UDO3:RK7S
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 No Proxy: hubproxy.docker.internal
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  hubproxy.docker.internal:5000
  localhost:5000
  127.0.0.0/8
 Live Restore Enabled: false

[gabyx]

Ok, using # syntax = docker/dockerfile:1.0 and and docker buildx build resolves this issue.