chore(ci): lint with golangci-lint (#726)

This introduces linting in CI to help maintain code quality and identify
issues that may not be caught by tests. To avoid a big PR that resolves
all existing linting issues, the CI workflow is configured to only look
at files that are changed in a particular PR or commit; we'll need to
keep an eye on this to make sure it's working as expected. This will
allow us to chip away at existing issues over time. Eventually (ideally
within a few months), the CI workflow should be updated to always lint
the entire codebase.

This PR also introduces a `make lint` task for local execution, but this
task lints the entire codebase and, for the time being, will catch some
issues that are not flagged for a particular PR or commit in CI.

.github/workflows/golangci-lint.yml

@@ -0,0 +1,30 @@
+name: golangci-lint
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+permissions:
+  contents: read
+  pull-requests: read # Remove along with only-new-issues by 2025
+jobs:
+  golangci:
+    name: lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: Determine golangci-lint version
+        id: golangcilint
+        run: |
+          line=$(grep GOLANGCI_LINT_VERSION= GNUmakefile)
+          version=$(echo ${line} | cut -d = -f2)
+          echo "version=$version" >> "$GITHUB_OUTPUT"
+      - name: golangci-lint
+        uses: golangci/golangci-lint-action@v6
+        with:
+          args: --whole-files # Remove along with only-new-issues by 2025
+          version: ${{ steps.golangcilint.outputs.version }}
+          only-new-issues: true # Remove along with pull-requests: read permission by 2025

.golangci.yaml

@@ -0,0 +1,13 @@
+run:
+  modules-download-mode: readonly
+  skip-dirs:
+    - cmd/migration-tool
+linters:
+  enable:
+    - errcheck
+    - goimports
+    - gosimple
+    - govet
+    - ineffassign
+    - staticcheck
+    - unused

GNUmakefile

@@ -11,6 +11,9 @@ ACCTEST_COUNT       ?= 1
 GOFMT_FILES         ?=$$(find . -name '*.go' |grep -v vendor)
 PKG_NAME            =equinix
 
+GOLANGCI_LINT_VERSION=v1.56
+GOLANGCI_LINT=go run github.com/golangci/golangci-lint/cmd/golangci-lint@${GOLANGCI_LINT_VERSION}
+
 ifneq ($(origin TESTS_REGEXP), undefined)
 	TESTARGS = -run='$(TESTS_REGEXP)'
 endif
@@ -45,6 +48,8 @@ clean:
 	${GOCMD} clean
 	rm -f ${BINARY}
 
+lint:
+	${GOLANGCI_LINT} run -v
 
 vet:
 	@echo "go vet ."
@@ -117,4 +122,4 @@ tfproviderdocs-check:
 		echo "Unexpected issues found in code with bflad/tfproviderdocs."; \
 		exit 1)
 
-.PHONY: test testacc build install clean  fmt fmtcheck errcheck test-compile docs-lint docs-lint-fix tfproviderlint tfproviderlint-fix tfproviderdocs-check
+.PHONY: test testacc build install clean lint fmt fmtcheck errcheck test-compile docs-lint docs-lint-fix tfproviderlint tfproviderlint-fix tfproviderdocs-check