Proposal: Expose Git information via build args

[mschfh]

This proposal builds upon the existing Git labels feature (#1290) which attaches Git metadata to images via labels.

Problem Statement

Currently, there's no simple way to access Git metadata during the build process or at runtime, as the BUILDX_GIT_LABELS feature only adds labels to the final image, they are not accessible during the build process.

Proposed Solution

Add a new config variable, (e.g. BUILDX_GIT_ARGS) that would expose the same Git metadata as build args, making them available during the build process. The build args would be similar to the existing labels:

Label	Build Arg
com.docker.image.source.entrypoint	SOURCEDOCKERFILE
org.opencontainers.image.revision	GITREVISION
org.opencontainers.image.source	GITSOURCE

This follows the same naming pattern as other automatic arguments like BUILDPLATFORM, TARGETARCH, etc.

Implementation

Similar to BUILDX_GIT_LABELS, this would be opt-in via an environment variable and would only work when building from a context with a .git directory.

Example Use Cases

• Conditional build logic based on Git state
  • Skip certain build steps when building from a "dirty" Git state
• Build-time decisions based on repository information
  • Include debug symbols only for development branches
• Version stamping during build process