multi stage builds: Error: determining starting point for build: no FROM statement found

[r10r]

Trying to set the base image name using a build argument fails in 1.37.5 for multi stage builds.
With buildah 1.33.6 this works as expected.

Example

ARG image_build
FROM $image_build as build
RUN echo foo >bar

ARG image_release
FROM $image_release
COPY --from=build bar bar

buildah bud --build-arg image_build=alpine:latest --build-arg image_release=alpine:3.20.3

[1/2] STEP 1/3: FROM alpine:latest AS build
[1/2] STEP 2/3: RUN echo foo >bar
[1/2] STEP 3/3: ARG image_release
Error: determining starting point for build: no FROM statement found

buildah --version
buildah version 1.37.5 (image-spec 1.1.0, runtime-spec 1.2.0)

[r10r]

To limit the bisect maybe a bit more: buildah v1.33.11 works fine too and 1.38.0 fails

[github-actions]

A friendly reminder that this issue had no activity for 30 days.

[flouthoc]

I can reproduce this, I'll take a look at this. Thanks for reporting.

[nalind]

FROM instructions can only reference args declared in the header of the file, i.e., the part of the file before the first FROM.
Despite appearances from the use of whitespace in the quoted example, the ARG image_release line is treated as part of the first stage.
Move the ARG image_release line to be just after the ARG image_build line (before FROM $image_build as build) , and you should be all set.