Use docker build for lint

This approach allows better caching of results (so faster subsequent
lints). It also avoids bind mounts which are slow.

Benchmarks on my machine (2017 MacBook Pro 13"):
* bind mount lint: 2m 38s
* new lint (after docker builder prune): 1m 35s
* old lint (rerun no changes): 2m 38s
* new lint (rerun added println in random Go file): 9s

Signed-off-by: Christopher Crone <[email protected]>

Dockerfile

@@ -1,5 +1,6 @@
 # syntax = docker/dockerfile:experimental
 ARG GO_VERSION=1.14.3-alpine
+ARG GOLANGCI_LINT_VERSION=1.27.0
 
 FROM golang:${GO_VERSION} AS base
 ARG TARGET_OS=unknown
@@ -32,14 +33,23 @@ ADD . ${PWD}
 FROM protos-base AS make-protos
 RUN make -f builder.Makefile protos
 
+FROM golangci/golangci-lint:v${GOLANGCI_LINT_VERSION}-alpine AS lint-base
+
+FROM base AS lint
+COPY --from=lint-base /usr/bin/golangci-lint /usr/bin/golangci-lint
+ENV CGO_ENABLED=0
+RUN --mount=id=build,type=cache,target=/root/.cache/go-build \
+    --mount=id=lint,type=cache,target=/root/.cache/golangci-lint \
+    make -f builder.Makefile lint
+
 FROM base AS make-cli
-RUN --mount=type=cache,target=/root/.cache/go-build \
+RUN --mount=id=build,type=cache,target=/root/.cache/go-build \
     GOOS=${TARGET_OS} \
     GOARCH=${TARGET_ARCH} \
-    make -f  builder.Makefile cli
+    make -f builder.Makefile cli
 
 FROM base AS make-cross
-RUN --mount=type=cache,target=/root/.cache/go-build \
+RUN --mount=id=build,type=cache,target=/root/.cache/go-build \
     make -f builder.Makefile cross
 
 FROM scratch AS protos

Makefile

@@ -62,7 +62,8 @@ cache-clear: ## Clear the builder cache
 	@docker builder prune --force --filter type=exec.cachemount --filter=unused-for=24h
 
 lint: ## run linter(s)
-	docker run --rm -t -v $(PWD):/app -w /app golangci/golangci-lint:v1.27-alpine golangci-lint run --timeout 10m0s ./...
+	@docker build . \
+	--target lint
 
 classic-link: ## create docker-classic symlink if does not already exist
 	ln -s /usr/local/bin/docker-classic /Applications/Docker.app/Contents/Resources/bin/docker
@@ -73,4 +74,4 @@ help: ## Show help
 
 FORCE:
 
-.PHONY: all protos cli e2e-local cross test cache-clear lint help classic-link
+.PHONY: all protos cli e2e-local cross test cache-clear lint classic-link help