COPY to a relative destination without WORKDIR set.

Problematic code:

FROM scratch
COPY foo bar

Correct code:

FROM scratch
COPY foo /bar

or

FROM scratch
WORKDIR /
COPY foo bar

Rationale:

While COPYing to a relative path is not problematic per sé, errors happen, when changes are introduced to the WORKDIR without updating the destination of the COPY command. Since it is easy to overlook this relationship, Hadolint emits this warning when no WORKDIR is set and COPY has a relative destination. This case is error prone and either setting the COPY-destination absolute or the WORKDIR explicitly will reduce the probability of having an error. It is assumed, that when a WORKDIR is set, the programmer will make sure it works well together with the destination of the COPY statements.