Changes for init/tidy

Dockerfile

@@ -2,12 +2,17 @@
 
 FROM --platform=${BUILDPLATFORM} golang:1.16.5-alpine AS base
 WORKDIR /src
-ENV CGO_ENABLED=0
+ENV CGO_ENABLED=1
+RUN apk update
+RUN apk add gcc g++
+RUN mkdir /out
+
+FROM base AS buildbase
 COPY go.* .
 RUN --mount=type=cache,target=/go/pkg/mod \
     go mod download
 
-FROM base AS build
+FROM buildbase AS build
 ARG TARGETOS
 ARG TARGETARCH
 RUN --mount=target=. \
@@ -31,6 +36,24 @@ RUN --mount=target=. \
     --mount=type=cache,target=/root/.cache/golangci-lint \
     golangci-lint run --timeout 10m0s ./...
 
+FROM base as mod-init-base
+WORKDIR /out
+COPY . .
+ENV MODNAME example
+RUN rm -f go.sum go.mod ; go mod init "${MODNAME}" && go mod tidy
+
+FROM base AS mod-tidy
+WORKDIR /out
+COPY . .
+RUN go mod tidy
+
+FROM scratch AS mod-init
+COPY --from=mod-init-base /out/go.mod /go.mod
+COPY --from=mod-init-base /out/go.sum /go.sum
+
+FROM scratch AS tidy
+COPY --from=mod-tidy /out/go.sum /go.sum
+
 FROM scratch AS unit-test-coverage
 COPY --from=unit-test /out/cover.out /cover.out
 

Makefile

@@ -28,8 +28,10 @@ lint:
 
 .PHONY: tidy
 tidy:
-	@docker run -t -i -v `pwd`:/src --workdir /src --rm golang:${UTIL_TAG} /usr/local/go/bin/go mod tidy
+	export DOCKER_BUILDKIT=1
+	@docker build . --target tidy --output .
 
 .PHONY: init
 init:
-	@docker run -t -i -v `pwd`:/src --workdir /src --rm golang:${UTIL_TAG} /usr/local/go/bin/go mod init
+	export DOCKER_BUILDKIT=1
+	@docker build . --target mod-init --output .