Use gofumpt if available, and enable gofumpt linter

gofumpt provides a supserset of gofmt / go fmt, but not every developer may have
it installed, so for situations where it's not available, fall back to gofmt.

As our code has been formatted with gofumpt already, in most cases contributions
will follow those formatting rules, but in some cases there may be a difference,
which would already be flagged by manual code review, but let's also enable the
gofumpt linter.

With this change, `make fmt` will use gofumpt is available; gofumpt has been
added to the dev-container, so `make -f docker.Makefile fmt` will always use it.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

.golangci.yml

@@ -4,6 +4,7 @@ linters:
     - depguard
     - dogsled
     - gocyclo
+    - gofumpt
     - goimports
     - gosec
     - gosimple

CONTRIBUTING.md

@@ -333,7 +333,7 @@ mind when nudging others to comply.
 
 The rules:
 
-1. All code should be formatted with `gofmt -s`.
+1. All code should be formatted with `gofumpt` (preferred) or `gofmt -s`.
 2. All code should pass the default levels of
    [`golint`](https://github.com/golang/lint).
 3. All code should follow the guidelines covered in [Effective

Makefile

@@ -5,6 +5,11 @@
 # Sets the name of the company that produced the windows binary.
 PACKAGER_NAME ?=
 
+# The repository doesn't have a go.mod, but "go list", and "gotestsum"
+# expect to be run from a module.
+GO111MODULE=auto
+export GO111MODULE
+
 all: binary
 
 _:=$(shell ./scripts/warn-outside-container $(MAKECMDGOALS))
@@ -45,8 +50,12 @@ shellcheck: ## run shellcheck validation
 	find scripts/ contrib/completion/bash -type f | grep -v scripts/winresources | grep -v '.*.ps1' | xargs shellcheck
 
 .PHONY: fmt
-fmt: ## run gofmt
-	go list -f {{.Dir}} ./... | xargs gofmt -w -s -d
+fmt: ## run gofumpt (if present) or gofmt
+	@if command -v gofumpt > /dev/null; then \
+		gofumpt -w -d -lang=1.19 . ; \
+	else \
+		go list -f {{.Dir}} ./... | xargs gofmt -w -s -d ; \
+	fi
 
 .PHONY: binary
 binary: ## build executable for Linux

docker.Makefile

@@ -76,7 +76,7 @@ shellcheck: ## run shellcheck validation
 	docker buildx bake shellcheck
 
 .PHONY: fmt
-fmt: ## run gofmt
+fmt: ## run gofumpt
 	$(DOCKER_RUN) $(DEV_DOCKER_IMAGE_NAME) make fmt
 
 .PHONY: vendor

dockerfiles/Dockerfile.dev

@@ -8,6 +8,14 @@ FROM docker/buildx-bin:${BUILDX_VERSION} AS buildx
 FROM golang:${GO_VERSION}-alpine AS golang
 ENV  CGO_ENABLED=0
 
+FROM golang AS gofumpt
+ARG GOFUMPT_VERSION=v0.4.0
+RUN --mount=type=cache,target=/root/.cache/go-build \
+    --mount=type=cache,target=/go/pkg/mod \
+    --mount=type=tmpfs,target=/go/src/ \
+    GO111MODULE=on go install "mvdan.cc/gofumpt@${GOFUMPT_VERSION}" \
+    && gofumpt --version
+
 FROM golang AS gotestsum
 ARG GOTESTSUM_VERSION=v0.4.0
 RUN --mount=type=cache,target=/root/.cache/go-build \
@@ -40,6 +48,7 @@ ENV DISABLE_WARN_OUTSIDE_CONTAINER=1
 ENV PATH=$PATH:/go/src/github.com/docker/cli/build
 
 COPY --from=buildx          /buildx /usr/libexec/docker/cli-plugins/docker-buildx
+COPY --from=gofumpt         /go/bin/* /go/bin/
 COPY --from=gotestsum       /go/bin/* /go/bin/
 COPY --from=goversioninfo   /go/bin/* /go/bin/