Mismatch between Dockerfile ARG reference and variable scoping documentation

[srgoni]

Is this a docs issue?

• My issue is about the documentation content or website

Type of issue

Information is incorrect

Description

The manual page about build variables describes automatic inheritance of ARGs between stages, but this is nowhere mentioned in the Dockerfile reference.

Variable scoping: https://docs.docker.com/build/building/variables/#scoping

Once a build argument is declared or consumed in a stage, it's automatically inherited by child stages.

Dockerfile reference: https://docs.docker.com/reference/dockerfile/#scope

An ARG instruction goes out of scope at the end of the build stage where it was defined. To use an argument in multiple stages, each stage must include the ARG instruction.

This can lead to confusion and unexpected behavior when relying on ARGs being scrubbed between stages.

Location

https://docs.docker.com/reference/dockerfile/#scope

Suggestion

Since the behavior described in the build variable manual matches what docker build does, it should also be mentioned in the Dockerfile reference.

[dvdksn]

Thanks for reporting, the fix has been merged upstream, and will be released with the next BuildKit release 👍🏻

[docker-robot]

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