Caching-friendly Makefile Rule to use Protoc within Docker

Makefile

PROTOS_SRC := $(wildcard ./api/*.proto)
GEN_SRC := $(PROTOS_SRC) Makefile
GEN_SUM := gen.sum
GO_PKG := moul.io/test
GO_DIR := ./go

.PHONY: clean
clean:
        rm -f gen.sum $(wildcard *.swagger.json)

.PHONY: generate
generate: gen.sum
$(GEN_SUM): $(GEN_SRC)
        shasum $(GEN_SRC) | sort -k 2 > $(GEN_SUM).tmp
        diff -q $(GEN_SUM).tmp $(GEN_SUM) || ( \
          set -e; \
          (set -e; cd $(GO_DIR) && GO111MODULE=on go mod vendor); \
          docker run \
            --user=`id -u` \
            --volume="$(PWD):/go/src/$(GO_PKG)" \
            --workdir="/go/src/$(GO_PKG)" \
            --entrypoint="sh" \
            --rm \
            moul/protoc-gen-gotemplate \
            -xec 'make generate_local' \
        )

.PHONY: generate_local
generate_local:
        protoc -I ../api:../go/vendor:/protobuf --swagger_out=logtostderr=true:. ../api/bertyprotocol.proto
        protoc -I ../api:../go/vendor:/protobuf --swagger_out=logtostderr=true:. ../api/bertychat.proto
        shasum $(GEN_SRC) | sort -k 2 > $(GEN_SUM).tmp
        mv $(GEN_SUM).tmp $(GEN_SUM)