Dockerfile comment line with continuation

[SvenDowideit]

I just commented out one line of a RUN command with a set of 's on the end (and when that errored out, moved the commented out line to just before the RUN

and the line continuation thus commented out the entire set :)

so I went from

RUN something && \
         else && \
         else && \
         else && \
         last

to

RUN something && \
#         else && \
         else && \
         else && \
         last

which quietly works ? to

#         else && \
RUN something && \
         else && \
         else && \
         last

and therefore the RUN was completely commented out.

We can either define this as 'works as intended' and so I'll document it, or decide that its a little too surprising (given that its a very hidden omission) and thus process the # before the \

@shykes @crosbymichael opinions?

[florentx]

I hit this one repeatedly :-/

[leandro-lucarella-sociomantic]

Hi, I will comment on this one even when is really old because I'm getting some deprecation message about this syntax.

I basically have this:

LABEL \
    maintainer="Me" \
    # Some comment about the next line
    description="Some image"

And I get this (docker-ce 17.09.0):

[WARNING]: Empty continuation line found in:
    LABEL     maintainer="Me"     description="Some image"
[WARNING]: Empty continuation lines will become errors in a future release.

I search for information about how line continuation and comments should be handled and couldn't find anything relevant except for this issue. I tried adding a \ and the end of the comment and is the same.

Given that is recommended everywhere to use line continuations with ENV and LABEL to avoid creating loads of layers (this is just an example, I have images with plenty of labels), it seems weird to have no clear solution to put comments in these multi-line commands.

Should I create a new issue about this?

[robertjpayne]

@leandro-lucarella-sociomantic same here, unsure if this is a regression or not?

[thaJeztah]

@leandro-lucarella-sociomantic @robertjpayne see #35004

[leandro-lucarella-sociomantic]

Ah, nice! Do you know if this will be part of a patch release or we'll have to wait until next full release to stop getting the deprecation messages?