strange issue when building image with build-arg on windows via Makefile

[Liu233w]

Description

Use the file below to reproduce it:

Makefile:

build:
	docker build . -f testArgPath.Dockerfile -t test-image --build-arg path=/var/testPath
run:
	docker run --rm test-image pwd
clean:
	docker image rm test-image

testArgPath.Dockerfile:

FROM alpine
ARG path
WORKDIR ${path}

running on windows via command prompt

Steps to reproduce the issue:

1. make build run clean

Describe the results you received:

d:\Sources\docker>make build run clean
docker build . -f testArgPath.Dockerfile -t test-image --build-arg path=/var/testPath
Sending build context to Docker daemon  4.096kB
Step 1/3 : FROM alpine
 ---> 3f53bb00af94
Step 2/3 : ARG path
 ---> Running in 1d0cea8985b2
Removing intermediate container 1d0cea8985b2
 ---> 05049de90a53
Step 3/3 : WORKDIR ${path}
 ---> Running in a778a99b6571
Removing intermediate container a778a99b6571
 ---> 264f464ff6fc
Successfully built 264f464ff6fc
Successfully tagged test-image:latest
SECURITY WARNING: You are building a Docker image from Windows against a non-Windows Docker host. All files and directories added to build context will have '-rwxr-xr-x' permissions. It is recommended to double check and reset permissions for sensitive files and directories.
docker run --rm test-image pwd
/D:/Software/msys2/var/testPath          <================== see this line =========
docker image rm test-image
Untagged: test-image:latest
Deleted: sha256:264f464ff6fc249e949fbfe5a7e5efd4c39481f8f9bcc9c58cfe8d25d83d7d85
Deleted: sha256:6442f5ad8e93b2e06f86c8e9acab852acfc5ea06255917e319be8aa0c9777f3d
Deleted: sha256:05049de90a53fd0bedbd61aff0431e92e260e8b02dbddf0db0c383c2217bd1f5

Describe the results you expected:

The output of pwd should be /var/testPath

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

I installed msys2 on windows to use make, by simply running pacman -S make and adding the bin path (d:\Software\msys2\usr\bin\ on my computer) of msys2 to the path environment variable.

Output of docker version:

docker on windows

docker version:

Docker version 18.09.0, build 4d60db4

docker desktop version:

Version 2.0.0.0-win81 (29211)
Channel: stable
Build: 4271b9e

Output of docker info:

Containers: 0
 Running: 0
 Paused: 0
 Stopped: 0
Images: 12
Server Version: 18.09.0
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 macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 468a545b9edcd5932818eb9de8e72413e616e86e
runc version: 69663f0bd4b60df09991c08812a60108003fa340
init version: fec3683
Security Options:
 seccomp
  Profile: default
Kernel Version: 4.9.125-linuxkit
Operating System: Docker for Windows
OSType: linux
Architecture: x86_64
CPUs: 2
Total Memory: 1.934GiB
Name: linuxkit-00155d35fc13
ID: H4F2:SVUL:BGTY:7PPJ:XJHS:3NJE:ZC3C:CSUD:4YFP:R3Z2:DMJO:BTEZ
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): true
 File Descriptors: 22
 Goroutines: 47
 System Time: 2018-12-31T17:26:27.8167808Z
 EventsListeners: 1
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
 127.0.0.0/8
Registry Mirrors:
 https://registry.docker-cn.com/
 http://8cc5e21c.m.daocloud.io/
Live Restore Enabled: false
Product License: Community Engine

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

[Liu233w]

I finally figured it out. Msys2 will correct the path automatically and change /var/testPath to /D:/Software/msys2/var/testPath in shell parameters. To fix that, just set environment variable MSYS2_ARG_CONV_EXCL="*" or add a line to the beginning of makefile like this:

export MSYS2_ARG_CONV_EXCL = *

build:
	echo $$MSYS2_ARG_CONV_EXCL
	docker build . -f testArgPath.Dockerfile -t test-image --build-arg path=/var/testPath
run:
	docker run --rm test-image pwd
clean:
	docker image rm test-image

the link that describe the feature: msys2/MSYS2-packages#84