Add makezero linter (#1520)

makezero ensures that objects recognized as slices are initialized with length 0.  By default, this is only required when we find a subsequent append to the object, but can also be enabled at all times as a way of discouraging the use of integer variables (i.e. "i") to index slices.

Author: ashanbrown

.golangci.example.yml

@@ -341,6 +341,9 @@ linters-settings:
   errorlint:
     # Report non-wrapping error creation using fmt.Errorf
     errorf: true
+  makezero:
+    # Allow only slices initialized with a length of zero. Default is false.
+    always: false
 
   # The custom section can be used to define linter plugins to be loaded at runtime. See README doc
   #  for more info.

go.mod

@@ -6,6 +6,7 @@ require (
 	4d63.com/gochecknoglobals v0.0.0-20201008074935-acfc0b28355a
 	github.com/Djarvur/go-err113 v0.0.0-20200511133814-5174e21577d5
 	github.com/OpenPeeDeeP/depguard v1.0.1
+	github.com/ashanbrown/makezero v0.0.0-20201205152432-7b7cdbb3025a
 	github.com/bombsimon/wsl/v3 v3.1.0
 	github.com/daixiang0/gci v0.2.4
 	github.com/denis-tingajkin/go-header v0.3.1

go.sum

@@ -266,6 +266,7 @@ type LintersSettings struct {
 	Exhaustive  ExhaustiveSettings
 	Gofumpt     GofumptSettings
 	ErrorLint   ErrorLintSettings
+	Makezero    MakezeroSettings
 
 	Custom map[string]CustomLinterSettings
 }
@@ -386,6 +387,10 @@ type ErrorLintSettings struct {
 	Errorf bool `mapstructure:"errorf"`
 }
 
+type MakezeroSettings struct {
+	Always bool
+}
+
 var defaultLintersSettings = LintersSettings{
 	Lll: LllSettings{
 		LineLength: 120,

pkg/config/config.go

@@ -0,0 +1,60 @@
+package golinters
+
+import (
+	"sync"
+
+	"github.com/ashanbrown/makezero/makezero"
+	"github.com/pkg/errors"
+	"golang.org/x/tools/go/analysis"
+
+	"github.com/golangci/golangci-lint/pkg/golinters/goanalysis"
+	"github.com/golangci/golangci-lint/pkg/lint/linter"
+	"github.com/golangci/golangci-lint/pkg/result"
+)
+
+const makezeroName = "makezero"
+
+func NewMakezero() *goanalysis.Linter {
+	var mu sync.Mutex
+	var resIssues []goanalysis.Issue
+
+	analyzer := &analysis.Analyzer{
+		Name: makezeroName,
+		Doc:  goanalysis.TheOnlyanalyzerDoc,
+	}
+	return goanalysis.NewLinter(
+		makezeroName,
+		"Finds slice declarations with non-zero initial length",
+		[]*analysis.Analyzer{analyzer},
+		nil,
+	).WithContextSetter(func(lintCtx *linter.Context) {
+		s := &lintCtx.Settings().Makezero
+
+		analyzer.Run = func(pass *analysis.Pass) (interface{}, error) {
+			var res []goanalysis.Issue
+			linter := makezero.NewLinter(s.Always)
+			for _, file := range pass.Files {
+				hints, err := linter.Run(pass.Fset, pass.TypesInfo, file)
+				if err != nil {
+					return nil, errors.Wrapf(err, "makezero linter failed on file %q", file.Name.String())
+				}
+				for _, hint := range hints {
+					res = append(res, goanalysis.NewIssue(&result.Issue{
+						Pos:        hint.Position(),
+						Text:       hint.Details(),
+						FromLinter: makezeroName,
+					}, pass))
+				}
+			}
+			if len(res) == 0 {
+				return nil, nil
+			}
+			mu.Lock()
+			resIssues = append(resIssues, res...)
+			mu.Unlock()
+			return nil, nil
+		}
+	}).WithIssuesReporter(func(*linter.Context) []goanalysis.Issue {
+		return resIssues
+	}).WithLoadMode(goanalysis.LoadModeSyntax | goanalysis.LoadModeTypesInfo)
+}

pkg/golinters/makezero.go

@@ -328,6 +328,9 @@ func (m Manager) GetAllSupportedLinterConfigs() []*linter.Config {
 			WithPresets(linter.PresetStyle).
 			WithLoadForGoAnalysis().
 			WithURL("https://github.com/kunwardeep/paralleltest"),
+		linter.NewConfig(golinters.NewMakezero()).
+			WithPresets(linter.PresetStyle, linter.PresetBugs).
+			WithURL("https://github.com/ashanbrown/makezero"),
 
 		// nolintlint must be last because it looks at the results of all the previous linters for unused nolint directives
 		linter.NewConfig(golinters.NewNoLintLint()).

pkg/lint/lintersdb/manager.go

@@ -0,0 +1,12 @@
+//args: -Emakezero
+package testdata
+
+func Makezero() []int {
+	x := make([]int, 5)
+	return append(x, 1) // ERROR "append to slice `x` with non-zero initialized length"
+}
+
+func MakezeroNolint() []int {
+	x := make([]int, 5)
+	return append(x, 1) //nolint:makezero // ok that we're appending to an uninitialized slice
+}

test/testdata/makezero.go

@@ -0,0 +1,13 @@
+//args: -Emakezero
+//config: linters-settings.makezero.always=true
+package testdata
+
+func MakezeroAlways() []int {
+	x := make([]int, 5) // ERROR "slice `x` does not have non-zero initial length"
+	return x
+}
+
+func MakezeroAlwaysNolint() []int {
+	x := make([]int, 5) //nolint:makezero // ok that this is not initialized
+	return x
+}