Add errnil linter.

go.mod

@@ -31,6 +31,7 @@ require (
 	github.com/golangci/revgrep v0.0.0-20210208091834-cd28932614b5
 	github.com/golangci/unconvert v0.0.0-20180507085042-28b1c447d1f4
 	github.com/gordonklaus/ineffassign v0.0.0-20210225214923-2e10b2664254
+	github.com/gostaticanalysis/nilerr v0.1.1
 	github.com/jgautheron/goconst v1.4.0
 	github.com/jingyugao/rowserrcheck v0.0.0-20210130005344-c6a0c12dd98d
 	github.com/jirfag/go-printf-func-name v0.0.0-20191110105641-45db9963cdd3

pkg/golinters/nilerr.go

@@ -0,0 +1,17 @@
+package golinters
+
+import (
+	"github.com/golangci/golangci-lint/pkg/golinters/goanalysis"
+	"github.com/gostaticanalysis/nilerr"
+	"golang.org/x/tools/go/analysis"
+)
+
+func NewNilErr() *goanalysis.Linter {
+	a := nilerr.Analyzer
+	return goanalysis.NewLinter(
+		a.Name,
+		"Finds the code that returns nil even if it checks that the error is not nil.",
+		[]*analysis.Analyzer{a},
+		nil,
+	).WithLoadMode(goanalysis.LoadModeTypesInfo)
+}

pkg/lint/lintersdb/manager.go

@@ -386,6 +386,10 @@ func (m Manager) GetAllSupportedLinterConfigs() []*linter.Config {
 			WithPresets(linter.PresetStyle).
 			WithLoadForGoAnalysis().
 			WithURL("https://github.com/julz/importas"),
+		linter.NewConfig(golinters.NewNilErr()).
+			WithLoadForGoAnalysis().
+			WithPresets(linter.PresetBugs).
+			WithURL("https://github.com/gostaticanalysis/nilerr"),
 
 		// nolintlint must be last because it looks at the results of all the previous linters for unused nolint directives
 		linter.NewConfig(golinters.NewNoLintLint()).

test/testdata/nilerr.go

@@ -0,0 +1,33 @@
+//args: -Enilerr
+package testdata
+
+func nilErr1() error {
+	err := nilErrDo()
+	if err == nil {
+		return err // ERROR `error is nil \(line 5\) but it returns error`
+	}
+
+	return nil
+}
+
+func nilErr2() error {
+	err := nilErrDo()
+	if err == nil {
+		return err // ERROR `error is nil \(line 14\) but it returns error`
+	}
+
+	return nil
+}
+
+func nilErr3() error {
+	err := nilErrDo()
+	if err != nil {
+		return nil // ERROR `error is not nil \(line 23\) but it returns nil`
+	}
+
+	return nil
+}
+
+func nilErrDo() error {
+	return nil
+}