c8a38c91dd
## Review A dedicated reviewer checked the rule description successfully for: - [ ] logical errors and incorrect information - [ ] information gaps and missing content - [ ] text style and tone - [ ] PR summary and labels follow [the guidelines](https://github.com/SonarSource/rspec/#to-modify-an-existing-rule) --------- Co-authored-by: Marcin Stachniuk <marcin.stachniuk@sonarsource.com>
85 lines
2.2 KiB
Plaintext
85 lines
2.2 KiB
Plaintext
The variable is not available in the current scope.
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It will be evaluated to an empty value.
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== Why is this an issue?
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The variables defined by `ARG` instruction have a scope from the definition to the end of the build stage where it was defined.
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If it was defined in the beginning of the Dockerfile (outside of any build stage), then its scope is restricted to only `FROM` instructions.
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Outside of their scope, variables will be resolved to empty string which may lead to unintended behaviour.
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== How to fix it
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=== Code examples
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==== Noncompliant code example
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[source,docker,diff-id=1,diff-type=noncompliant]
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----
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ARG SETTINGS
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FROM busybox
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RUN ./run/setup $SETTINGS
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----
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In this case the `$SETTINGS` variable will be evaluated to empty string.
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==== Compliant solution
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[source,docker,diff-id=1,diff-type=compliant]
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----
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FROM busybox
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ARG SETTINGS
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RUN ./run/setup $SETTINGS
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----
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In this case when Dockerfile will be built with the flag `--build-arg SETTINGS=--some-settings` the flag `--some-settings` will be passed to the `RUN` instruction.
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==== Noncompliant code example
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[source,docker,diff-id=2,diff-type=noncompliant]
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----
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ARG SETTINGS="--default-settings"
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FROM busybox
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RUN ./run/setup $SETTINGS
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----
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In this case the `$SETTINGS` variable will be evaluated to empty string.
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==== Compliant solution
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[source,docker,diff-id=2,diff-type=compliant]
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----
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ARG SETTINGS="--default-settings"
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FROM busybox
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ARG SETTINGS
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RUN ./run/setup $SETTINGS
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----
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In this case the flag `--default-settings` will be passed to `RUN` instruction (unless another value is provided during build time).
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=== How does this work?
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The `FROM` instruction starts a new build stage where variables defined by previous `ARG` instructions are out of this new scope.
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To make it accessible for the build stage they need to be defined after the `FROM` instruction.
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== Resources
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=== Documentation
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* https://docs.docker.com/engine/reference/builder/#scope[ARG scope - Dockerfile reference]
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Include the `ARG` instruction in the build stage where it is used.
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=== Highlighting
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Highlight usage of the variable where it is not accessible.
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'''
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endif::env-github,rspecator-view[]
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