LABEL error is unclear when quotes are misused

[alexcb]

VERSION 0.7

test:
  FROM alpine
  RUN echo https://github.com/earthly/earthly > url
  LABEL "org.opencontainers.image.source=$(cat url)"

fails:

Error: build target: build main: failed to solve: resolve build context for target +test: Earthfile line 6:52 '
': invalid syntax

[alexcb]

https://github.com/earthly/earthly/blob/main/earthfile2llb/interpreter.go#L1423-L1444 makes calls to expand args, but it's not clear how "org.opencontainers.image.source=$(cat url)" ends up being split into "org.opencontainers.image.source", "=", $(cat url)"

[alexcb]

Note that this does work

VERSION 0.7

test:
  FROM alpine
  RUN echo https://github.com/earthly/earthly > url
  LABEL org.opencontainers.image.source="$(cat url)"   # note the quotes are located after the `=`.

[alexcb]

this too works:

VERSION 0.7

test:
  FROM alpine
  RUN echo https://github.com/earthly/earthly > url
  LABEL org.opencontainers.image.source=$(cat url)

[alexcb]

stretch goal: currently LABEL only appears under:

$ head tests/smoke.earth
VERSION 0.7
# This is a smoke test for parsing. We don't actually check that the config was
# set correctly.
FROM alpine:3.15
test:
    LABEL a=b c=d "e    eee = ee"=fff
    LABEL x=y
    LABEL abc.def.ghi=jkl

we should create an integration test that validates the label is correctly produced in the built image.

[nelsam]

For clarification's sake: LABEL "org.opencontainers.image.source"="$(cat url)" also works.

LABEL "somelabel=somevalue" should not be valid syntax, correct? The issue mentions "org.opencontainers.image.source=$(cat url)", but that is one value - we should not split on the equals sign there. Since the = is inside of the quote pair, that equates to LABEL labelKey, and our parser grammar requires a label statement to be LABEL (labelKey EQUALS labelValue)* - so the = cannot be inside of the quote pair to be valid syntax.

The error message is obtuse (and this is not the only case where an error message is obtuse), so I would like to improve the error message - but I want to make sure that the problem is specifically that the error message is not clear enough to track down why the LABEL failed.

[alexcb]

LABEL "somelabel=somevalue" should not be valid syntax, correct?

That's a really good point.

where as LABEL "$KEY"="$VALUE" should be valid (as you point out, it already works).

It seems like the only issue is the error is not obvious.