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.