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Adjacent LABEL instructions in the same stage are easier to review when they are written as a single multi-line LABEL block.
PropertyValue
SeverityInfo
CategoryStyle
DefaultEnabled
Auto-fixYes

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Description

Modern Docker no longer needs separate LABEL instructions to keep image layers small, so scattered LABELs serve no build purpose. Grouping them into one multi-line block keeps related image metadata together, makes diffs easier to read, and reduces the chance that two unrelated edits land on different lines of the same logical metadata block. The rule reports when a stage has at least min-labels label key/value pairs spread across two or more adjacent LABEL instructions. Two LABEL instructions are considered adjacent only when no other Dockerfile instruction (such as ARG, ENV, or RUN) and no comment line appears between them. Comments are treated as deliberate section breaks and never crossed by the auto-fix. This rule does not reorder labels. Stable ordering is left to a separate rule.

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Auto-fix

The fix replaces the first LABEL instruction in the run with one multi-line LABEL containing every pair from the run, and deletes the remaining LABEL instructions in the run. Pairs are emitted in source order so that Docker’s “last value wins” rule still produces the same effective image label map. The fix is suppressed when:
  • a key in the run is dynamic (for example LABEL "$PREFIX.name"=...)
  • a pair uses the legacy LABEL key value form
  • the run contains a duplicate key (let tally/labels/no-duplicate-keys rewrite the duplicate first)
The fix output uses the same shape that tally/newline-per-chained-call produces for split LABELs, so the two rules agree on a single canonical form and a re-lint after fixing is clean.

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Examples

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Bad

FROM alpine:3.20

LABEL org.opencontainers.image.title="demo"
LABEL org.opencontainers.image.description="example image"
LABEL org.opencontainers.image.source="https://github.com/example/demo"
LABEL org.opencontainers.image.licenses="Apache-2.0"

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Good

FROM alpine:3.20

LABEL org.opencontainers.image.title="demo" \
      org.opencontainers.image.description="example image" \
      org.opencontainers.image.source="https://github.com/example/demo" \
      org.opencontainers.image.licenses="Apache-2.0"

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Configuration

[rules.tally.labels.prefer-grouped]
severity = "info"
min-labels = 3
OptionTypeDefaultDescription
min-labelsinteger (>= 2)3Minimum total label key/value pairs across an adjacent run before the rule reports.