Makefile+github: add make fmt-check to check for formatting

.github/workflows/main.yml

@@ -32,6 +32,24 @@ env:
   GO_VERSION: 1.18.2
 
 jobs:
+  ########################
+  # format code
+  ########################
+  fmt-check:
+    name: check code format
+    runs-on: ubuntu-latest
+    steps:
+      - name: git checkout
+        uses: actions/checkout@v3
+
+      - name: setup go ${{ env.GO_VERSION }}
+        uses: actions/setup-go@v3
+        with:
+          go-version: '${{ env.GO_VERSION }}'
+
+      - name: fmt
+        run: make fmt-check
+
   ########################
   # RPC and mobile compilation check
   ########################

Makefile

@@ -258,6 +258,10 @@ fmt: $(GOIMPORTS_BIN)
 	@$(call print, "Formatting source.")
 	gofmt -l -w -s $(GOFILES_NOVENDOR)
 
+fmt-check: fmt
+	@$(call print, "Checking fmt results.")
+	if test -n "$$(git status --porcelain)"; then echo "code not formatted correctly, please run `make fmt` again!"; git status; git diff; exit 1; fi
+
 lint: docker-tools
 	@$(call print, "Linting source.")
 	$(DOCKER_TOOLS) golangci-lint run -v $(LINT_WORKERS)

docs/release-notes/release-notes-0.16.0.md

@@ -45,6 +45,9 @@ transaction](https://github.com/lightningnetwork/lnd/pull/6730).
 * [The `golangci-lint` tool was updated to
   `v1.46.2`](https://github.com/lightningnetwork/lnd/pull/6731)
 
+* Updated the github actions to use `make fmt-check` in its [build
+  process](https://github.com/lightningnetwork/lnd/pull/6853).
+
 # Contributors (Alphabetical Order)
 
 * Carla Kirk-Cohen