Cross-build step with multiplatform build logging is ambiguous

[cpuguy83]

When performing a build step such as this example:

FROM --platform=$BUILDPLATFORM AS hello
RUN echo hello; sleep 10

And then building for multiple target platforms, it is difficult to tell which platform target is running or failed because the output effectively shows BUILDPLATFORM (in this case).

Example from above might look like this even though I'm building for both linux/amd64 and linux/arm64, both only show linux/amd64:

[ linux/amd64 hello 1/1 ] RUN  echo hello; sleep 10
hello
[ linux/amd64 hello 1/1 ] RUN  echo hello; sleep 10
hello

[tonistiigi]

Showing linux/amd64 in there is correct as the hello/sleep binary running there is linux/amd64 but as it is confusing we could detect the case where TARGETPLATFORM for Dockerfile stage is not the same as current platform and show both then.

[chendave]

+1

[chendave]

/assign

[chendave]

if anyone want a quick fix, pls feel free to assign this to yourself.

[pkoenig10]

Fixed by #2576