False positive flagged if quotes used when replacing variables in an ARG, ENV, or LABEL

[rcjsuen]

The following Dockerfile will built without any problems. We need to fix the validator so that it doesn't consider the ENV instruction to be an error.

FROM scratch
ARG BUNDLE_WITHOUT
ENV BUNDLE_WITHOUT=${bundle_without:-'development test'}

$ dockerfile-utils lint Dockerfile
Line: 3
ENV BUNDLE_WITHOUT=${bundle_without:-'development test'}
                                                       ^
Error: Syntax error - can't find = in "}". Must be of the form: name=value

$ docker build .
Sending build context to Docker daemon  1.693MB
Step 1/3 : FROM scratch
 --->
Step 2/3 : ARG BUNDLE_WITHOUT
 ---> Running in 7cc436e68ec3
Removing intermediate container 7cc436e68ec3
 ---> 64a3e0a2f136
Step 3/3 : ENV BUNDLE_WITHOUT=${bundle_without:-'development test'}
 ---> Running in c148dc76c691
Removing intermediate container c148dc76c691
 ---> a608dc772a5d
Successfully built a608dc772a5d

[rcjsuen]

Since ENV and LABEL is written in the same way, LABEL instructions also suffer from this same problem.

FROM scratch
LABEL BUNDLE_WITHOUT=${bundle_without:-'development test'}

$ dockerfile-utils lint Dockerfile
Line: 2
LABEL BUNDLE_WITHOUT=${bundle_without:-'development test'}
                                                         ^
Error: Syntax error - can't find = in "}". Must be of the form: name=value

$ docker build .
Sending build context to Docker daemon  1.695MB
Step 1/2 : FROM scratch
 --->
Step 2/2 : LABEL BUNDLE_WITHOUT=${bundle_without:-'development test'}
 ---> Running in 2714ad3002f9
Removing intermediate container 2714ad3002f9
 ---> 02682ef791a9
Successfully built 02682ef791a9

[rcjsuen]

I don't think any code changes will be necessary on this end. Should just need to adopt the new version of dockerfile-ast after rcjsuen/dockerfile-ast#24 has been fixed.

[rcjsuen]

Same problem applies to ARG instructions although the error isn't quite the same.

FROM scratch
ARG BUNDLE_WITHOUT=${bundle_without:-'development test'}

$ dockerfile-utils lint Dockerfile
Line: 2
ARG BUNDLE_WITHOUT=${bundle_without:-'development test'}
                                                       ^
Error: ARG requires exactly one argument

$ docker build .
Sending build context to Docker daemon  1.695MB
Step 1/2 : FROM scratch
 --->
Step 2/2 : ARG BUNDLE_WITHOUT=${bundle_without:-'development test'}
 ---> Running in 0ec9a4a58d65

Removing intermediate container 0ec9a4a58d65
 ---> 6e9479050949
Successfully built 6e9479050949