Dynamic Go workspace Docker build contexts

!DockerGoWorkspaces.md

(gist title)

This gist assumes the following directory structure:

• foobar-ws/
  • bar/
    • bar.go
    • go.mod
  • foo/
    • foo.go
    • go.mod
  • foobar/
    • deployments/foobar/
      • Dockerfile
    • go.mod
    • go.sum
    • main.go
    • Makefile

Dockerfile

FROM scratch as empty

FROM golang:1.20-alpine AS builder
ARG WSDISKPATHS
ARG MOD1=./
ARG MOD2=./
ARG MOD3=./
ARG MOD4=./
ARG MOD5=./
ARG MOD6=./
ARG MOD7=./
ARG MOD8=./
ARG MOD9=./

WORKDIR /ws
# Copy the additionally used modules into the soon-to-be workspace.
COPY --from=bctx1 . ${MOD1}
COPY --from=bctx2 . ${MOD2}
COPY --from=bctx3 . ${MOD3}
COPY --from=bctx4 . ${MOD4}
COPY --from=bctx5 . ${MOD5}
COPY --from=bctx6 . ${MOD6}
COPY --from=bctx7 . ${MOD7}
COPY --from=bctx8 . ${MOD8}
COPY --from=bctx9 . ${MOD9}

# Finally copy in the main module containing a main package to be build.
WORKDIR /ws/foobar
COPY go.mod go.sum ./
RUN go mod download
COPY *.go ./

# Establish the Go workspace
WORKDIR /ws
RUN go work init ${WSDISKPATHS}
RUN go build -v -o /foobar ./foobar

Makefile

MAINUSE:=./foobar
EMPTYCONTEXT:=.emptyctx
NUMCONTEXTS:=9

SHELL:=/bin/bash

build:
	@# find out if we are in workspace mode -- and it we are, then the list of
	@# modules actually used.
	@mkdir -p $(EMPTYCONTEXT); \
	trap 'rm -rf -- "$(EMPTYCONTEXT)"' EXIT; \
	contexts=(); \
	workspace_details=$$(go work edit --json); \
	if [[ $${workspace_details} ]]; then \
		goworkdir=$$(dirname $$(go env GOWORK)); \
		echo "found workspace" $${goworkdir}; \
		diskpaths=$$(echo $${workspace_details} | jq --raw-output '.Use | .[]? | .DiskPath'); \
		echo "modules used in workspace:" $${diskpaths}; \
		while IFS= read -r module; do \
			if [[ "$${module}" == "$(MAINUSE)" ]]; then \
				echo "  🏠" $${module}; \
			else \
				relcontext=$$(realpath --relative-to="." $${goworkdir}/$${module}); \
				contexts+=( $${relcontext} ); \
				echo "  🧩" $${module} "» 📁" $${relcontext}; \
			fi \
		done <<< $${diskpaths}; \
	else \
		diskpaths="$(MAINUSE)"; \
	fi; \
	buildctxargs=(); \
	buildargs=(); \
	ctxno=1; \
	for ctx in "$${contexts[@]}"; do \
		buildctxargs+=( "--build-context=bctx$${ctxno}=$${ctx}" ); \
		buildargs+=( "--build-arg=MOD$${ctxno}=./$$(basename ./$${ctx})/" ); \
		((ctxno=ctxno+1)); \
	done; \
	for ((;ctxno<=$(NUMCONTEXTS);ctxno++)); do \
		buildctxargs+=( "--build-context=bctx$${ctxno}=$(EMPTYCONTEXT)" ); \
	done; \
	echo "args:" $${buildctxargs[*]} $${buildargs[*]}; \
	echo "build inside:" $${CWD}; \
	docker build \
		-f ./deployments/foobar/Dockerfile \
		$${buildargs[@]} \
		$${buildctxargs[@]} \
		--build-arg=WSDISKPATHS="$$(echo $${diskpaths})" \
		.