False positive caused by ARG that continues to nothing

[rcjsuen]

The following unrealistic Dockerfile builds just fine.

FROM scratch
ARG var=value \
# var2=value2

$ docker build .
Sending build context to Docker daemon  1.774MB
Step 1/2 : FROM scratch
 --->
Step 2/2 : ARG var=value
 ---> Running in 39d20b950664
Removing intermediate container 39d20b950664
 ---> 52bd1fd4e9ae
Successfully built 52bd1fd4e9ae

However, the validator will flag an error. Note also that the range of the highlighted content seems weird as it includes the whitespace between ARG and var=value as well as the whitespace after the var=value.

$ docker run -v `pwd`/Dockerfile:/Dockerfile rcjsuen/dockerfile-utils lint /Dockerfile
Line: 2
ARG var=value \
   ^^^^^^^^^^^
Error: ARG requires exactly one argument

[rcjsuen]

This looks like a bug in dockerfile-ast and not the validator.

[rcjsuen]

This is caused by rcjsuen/dockerfile-ast#40.