ci: Switch from gometalinter to golangci-lint

The former is deprecated in favour of the later, which is faster and less
memory hungry.

The `.golangci.yml` is a straight translation of the enabled linters and
exclusions from `gometalinter.json`, except:

- The exclusions of `specification/bindata.go` and `templateloader` no longer
  seem relevant (nothing hits, the latter no longer exists) so those are
  dropped.
- I didn't copy over the various tweaks to output formats (the `sort` key) nor
  the deadline setting.
- There is currently no equivalent to the `WarnUnmatchedDirective` key, see
  golangci/golangci-lint#404
- The `unparam` linter now catches a few things which it didn't before, these
  are fixed here:

    pkg/yatee/yatee.go:131:39: tokenize - result 1 (error) is always nil (unparam)
    func tokenize(expr string) ([]string, error) {
                                          ^
    pkg/yatee/yatee_test.go:31:47: `testProcess` - `parameters` always receives `parameters` (`"\nfoo: bar\nloop: $loop\napp:\n  mode: debug\n  release: false\n  co...`) (unparam)
    func testProcess(t *testing.T, input, output, parameters, error string) {
                                                  ^
    pkg/yatee/yatee_test.go:147:56: `testProcessWithOrder` - `error` is unused (unparam)
    func testProcessWithOrder(t *testing.T, input, output, error string) {
                                                           ^

  The first and third by dropping the unused return value and parameter
  respectively. For the middle one I marked as `nolint` since it makes sense to
  keep `parameters` defined in the caller since they are combined with `input`
  to produce `output` and it is useful to have them in the same context.

The `nakedret` linter is part of `golangci-lint` already so there is no need to
add it separately.

Signed-off-by: Ian Campbell <ijc@docker.com>

Author: Ian Campbell

.golangci.yml

@@ -0,0 +1,24 @@
+linters:
+  enable-all: false
+  disable-all: true
+  enable:
+    - deadcode
+    - gocyclo
+    - gofmt
+    - goimports
+    - golint
+    - gosimple
+    - ineffassign
+    - interfacer
+    - lll
+    - misspell
+    - nakedret
+    - unconvert
+    - unparam
+    - unused
+    - vet
+linters-settings:
+  gocyclo:
+    min-complexity: 16
+  lll:
+    line-length: 200

Dockerfile.lint

@@ -8,18 +8,8 @@ RUN apk add --no-cache \
     make \
     coreutils
 
-ENV GOMETALITER_VERSION=2.0.11
-ENV NAKEDRECT_SHA=c0e305a4f690fed163d47628bcc06a6d5655bf92
-
-WORKDIR /go/src/github.com/alecthomas/gometalinter
-RUN curl -L https://github.com/alecthomas/gometalinter/archive/v${GOMETALITER_VERSION}.tar.gz | tar xz --strip-components=1 \
-    && go build -v -o /usr/local/bin/gometalinter . \
-    && gometalinter --install \
-    && rm -rf /go/src/* /go/pkg/*
-
-WORKDIR /go/src/github.com/alexkohler/nakedret
-RUN git clone https://github.com/alexkohler/nakedret.git /go/src/github.com/alexkohler/nakedret \
-    && go build -v -o /usr/local/bin/nakedret . \
+RUN GO111MODULE=on go get \
+    github.com/golangci/golangci-lint/cmd/golangci-lint@v1.16.0 \
     && rm -rf /go/src/* /go/pkg/*
 
 WORKDIR /go/src/github.com/docker/app

Makefile

@@ -73,7 +73,7 @@ test: test-unit test-e2e ## run all tests
 
 lint: ## run linter(s)
 	@echo "Linting..."
-	@gometalinter --config=gometalinter.json ./...
+	@golangci-lint run ./...
 
 test-e2e: bin/$(BIN_NAME) ## run end-to-end tests
 	@echo "Running e2e tests..."

gometalinter.json

@@ -128,7 +128,7 @@ func extract(expr string) (string, error) {
 	return expr[0:i], nil
 }
 
-func tokenize(expr string) ([]string, error) {
+func tokenize(expr string) []string {
 	var tokens []string
 	p := 0
 	for p < len(expr) {
@@ -145,7 +145,7 @@ func tokenize(expr string) ([]string, error) {
 			p++
 		}
 	}
-	return tokens, nil
+	return tokens
 }
 
 func evalValue(comps []string, i int) (int64, int, error) {
@@ -199,10 +199,7 @@ func evalSub(comps []string, i int) (int64, int, error) {
 
 // resolves an arithmetic expression
 func evalExpr(expr string) (int64, error) {
-	comps, err := tokenize(expr)
-	if err != nil {
-		return 0, err
-	}
+	comps := tokenize(expr)
 	v, _, err := evalSub(comps, 0)
 	return v, err
 }

pkg/yatee/yatee.go

@@ -28,7 +28,10 @@ func TestEval(t *testing.T) {
 	testEval(t, "${foo?foo:bar}", env, "foo")
 }
 
-func testProcess(t *testing.T, input, output, parameters, error string) {
+// The nolint is because `parameters` is always the same, but it is
+// preferable to keep the definition in the caller since it
+// corresponds to `input` and `output`.
+func testProcess(t *testing.T, input, output, parameters, error string) { //nolint:unparam
 	ps := make(map[interface{}]interface{})
 	err := yaml.Unmarshal([]byte(parameters), ps)
 	assert.NilError(t, err)
@@ -144,7 +147,7 @@ ab:
 		"eval loop detected")
 }
 
-func testProcessWithOrder(t *testing.T, input, output, error string) {
+func testProcessWithOrder(t *testing.T, input, output string) {
 	parameters := make(map[string]interface{})
 
 	res, err := ProcessWithOrder(input, parameters)
@@ -164,7 +167,7 @@ func TestProcessWithOrder(t *testing.T) {
 `, `parent:
   bb: true
   aa: false
-`, "")
+`)
 
 	// Test ordering is preserved at the top level
 	testProcessWithOrder(t,
@@ -176,5 +179,5 @@ aaa:
   nested: true
 aaa:
   nested: false
-`, "")
+`)
 }