refactor: change the stages for embed files generation

The main goal to avoid cache invalidation on `tag` changes: by pushing
the tag down the build after the generate step, avoid invalidating build
cache on each tag change (`-dirty`, rebasing, etc.)

Signed-off-by: Andrey Smirnov <andrey.smirnov@talos-systems.com>

Dockerfile

@@ -137,23 +137,6 @@ ENV PROTOTOOL_CACHE_PATH /.cache/prototool
 ARG SOURCE_DATE_EPOCH
 ENV SOURCE_DATE_EPOCH ${SOURCE_DATE_EPOCH}
 WORKDIR /src
-ARG NAME
-ARG SHA
-ARG USERNAME
-ARG REGISTRY
-ARG TAG
-ARG ARTIFACTS
-ARG PKGS
-ARG EXTRAS
-RUN mkdir -p pkg/machinery/gendata/data && \
-    echo -n ${NAME} > pkg/machinery/gendata/data/name && \
-    echo -n ${SHA} > pkg/machinery/gendata/data/sha && \
-    echo -n ${USERNAME} > pkg/machinery/gendata/data/username && \
-    echo -n ${REGISTRY} > pkg/machinery/gendata/data/registry && \
-    echo -n ${EXTRAS} > pkg/machinery/gendata/data/extras && \
-    echo -n ${PKGS} > pkg/machinery/gendata/data/pkgs && \
-    echo -n ${TAG} > pkg/machinery/gendata/data/tag && \
-    echo -n ${ARTIFACTS} > pkg/machinery/gendata/data/artifacts
 
 # The build-go target creates a container to build Go code with Go modules downloaded and verified.
 
@@ -226,11 +209,36 @@ RUN --mount=type=cache,target=/.cache go generate ./...
 RUN goimports -w -local github.com/talos-systems/talos ./
 RUN gofumpt -w ./
 
-FROM build AS fix_embed
+FROM build AS embed-generate
+ARG NAME
+ARG SHA
+ARG USERNAME
+ARG REGISTRY
+ARG TAG
+ARG ARTIFACTS
+ARG PKGS
+ARG EXTRAS
+RUN mkdir -p pkg/machinery/gendata/data && \
+    echo -n ${NAME} > pkg/machinery/gendata/data/name && \
+    echo -n ${SHA} > pkg/machinery/gendata/data/sha && \
+    echo -n ${USERNAME} > pkg/machinery/gendata/data/username && \
+    echo -n ${REGISTRY} > pkg/machinery/gendata/data/registry && \
+    echo -n ${EXTRAS} > pkg/machinery/gendata/data/extras && \
+    echo -n ${PKGS} > pkg/machinery/gendata/data/pkgs && \
+    echo -n ${TAG} > pkg/machinery/gendata/data/tag && \
+    echo -n ${ARTIFACTS} > pkg/machinery/gendata/data/artifacts
+
+FROM scratch AS embed
+COPY --from=embed-generate /src/pkg/machinery/gendata/data /pkg/machinery/gendata/data
+
+FROM embed-generate AS embed-abbrev-generate
 ARG ABBREV_TAG
 RUN echo -n "undefined" > pkg/machinery/gendata/data/sha && \
     echo -n ${ABBREV_TAG} > pkg/machinery/gendata/data/tag
 
+FROM scratch AS embed-abbrev
+COPY --from=embed-abbrev-generate /src/pkg/machinery/gendata/data /pkg/machinery/gendata/data
+
 FROM --platform=${BUILDPLATFORM} scratch AS generate
 COPY --from=proto-format-build /src/api /api/
 COPY --from=generate-build /api/common/*.pb.go /pkg/machinery/api/common/
@@ -247,7 +255,7 @@ COPY --from=go-generate /src/pkg/machinery/resources/network/ /pkg/machinery/res
 COPY --from=go-generate /src/pkg/machinery/config/types/v1alpha1/ /pkg/machinery/config/types/v1alpha1/
 COPY --from=go-generate /src/pkg/machinery/nethelpers/ /pkg/machinery/nethelpers/
 COPY --from=go-generate /src/pkg/machinery/extensions/ /pkg/machinery/extensions/
-COPY --from=fix_embed /src/pkg/machinery/gendata/data /pkg/machinery/gendata/data
+COPY --from=embed-abbrev / /
 
 # The base target provides a container that can be used to build all Talos
 # assets.
@@ -257,7 +265,7 @@ COPY ./cmd ./cmd
 COPY ./pkg ./pkg
 COPY ./internal ./internal
 COPY --from=generate /pkg/machinery/ ./pkg/machinery/
-COPY --from=build /src/pkg/machinery/gendata/data ./pkg/machinery/gendata/data
+COPY --from=embed / ./
 RUN --mount=type=cache,target=/.cache go list all >/dev/null
 WORKDIR /src/pkg/machinery
 RUN --mount=type=cache,target=/.cache go mod download