Publish diagnostic if COPY instruction has an insufficient number of arguments

[rcjsuen]

FROM alpine AS dev
COPY --from=dev

$ docker build .
Sending build context to Docker daemon  86.15MB
Step 1/2 : FROM alpine AS dev
 ---> 7328f6f8b418
Step 2/2 : COPY --from=dev
COPY requires at least two arguments

As can be seen above, a COPY instruction requires two arguments for it to be a valid. However, with the use of the --from flag, an error complaining about COPY requiring two arguments may appear even if you do indeed have two arguments.

FROM alpine AS dev
COPY --from=dev .

$ docker build .
Sending build context to Docker daemon  86.15MB
Step 1/2 : FROM alpine AS dev
 ---> 7328f6f8b418
Step 2/2 : COPY --from=dev .
COPY requires at least two arguments