"ARG requires exactly one argument" dockerfile-utils(4)

[oberfoerster]

in Dockerfile:

...
ARG BUILD_ARG1=23 \
    BUILD_ARG2=42
...

renders following warning from dockerfile-utils: "ARG requires exactly one argument" albeit everything building and working as expected.

ENV:

Version: 1.43.2
Commit: 0ba0ca52957102ca3527cf479571617f0de6ed50
Date: 2020-03-24T07:52:11.516Z
Electron: 7.1.11
Chrome: 78.0.3904.130
Node.js: 12.8.1
V8: 7.8.279.23-electron.0
OS: Linux x64 3.10.0-1160.11.1.el7.x86_64

[bwateratmsft]

I guess it's debatable; the spec for ARG implies (but doesn't overtly state) that it takes only one item, optionally with a default value.

ARG <name>[=<default value>]

As an example for multiple, it gives the following:

FROM busybox
ARG user1
ARG buildno
# ...

@rcjsuen what do you think?

[ucheNkadiCode]

@rcjsuen, do you think it's possible to make this dockerfile specification a little more flexible to include the user's ARG use case? The phrase "requires" makes it seem like their example won't run when it will.

[rcjsuen]

First of all, thank you to @oberfoerster for the bug report and my apologies for the late response. Been flooded with GitHub notifications and I haven't yet gotten around to pruning things down so this fell through the cracks. :(

So, with regards to ARG instructions taking in multiple arguments, that is a new feature introduced by moby/buildkit#1692 in the 20.10 release. I'll make the change in the language server so that this is no longer flagged as an error.

[bwateratmsft]

Cool, didn't know it was explicitly added as a new capability. Thanks!

[oberfoerster]

Thank You!
Seems, I'm an early adopter then ;)

[rcjsuen]

@oberfoerster I've opened #2866 to fix this.