logcheck: support new golangci-lint plugin interface

The new plugin interface was added in golangci/golangci-lint#3887
to allow settings for custom plugins. This commit implements the new
plugin interface with `config` value in the settings, and passes it
to flag `--config`.

go.mod

@@ -3,6 +3,7 @@ module sigs.k8s.io/logtools
 go 1.15
 
 require (
+	github.com/mitchellh/mapstructure v1.5.0 // indirect
 	golang.org/x/exp v0.0.0-20210220032938-85be41e4509f
 	golang.org/x/tools v0.1.12
 )

go.sum

@@ -1,6 +1,8 @@
 dmitri.shuralyov.com/gpu/mtl v0.0.0-20201218220906-28db891af037/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20200222043503-6f7a984d4dc4/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
+github.com/mitchellh/mapstructure v1.5.0 h1:jeMsZIYE/09sWLaz43PL7Gy6RuMjD2eJVyuac5Z2hdY=
+github.com/mitchellh/mapstructure v1.5.0/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RRV2QTWOzhPopBRo=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=

logcheck/plugin/plugin.go

@@ -19,6 +19,7 @@ limitations under the License.
 package main
 
 import (
+	"github.com/mitchellh/mapstructure"
 	"golang.org/x/tools/go/analysis"
 	"sigs.k8s.io/logtools/logcheck/pkg"
 )
@@ -33,3 +34,26 @@ func (*analyzerPlugin) GetAnalyzers() []*analysis.Analyzer {
 
 // AnalyzerPlugin is the entry point for golangci-lint.
 var AnalyzerPlugin analyzerPlugin
+
+// Settings is the value struct passed by golangci-lint.
+type Settings struct {
+	Config string
+}
+
+// New is the entry point for golangci-lint, which takes priority over AnalyzerPlugin.
+func New(conf interface{}) ([]*analysis.Analyzer, error) {
+	a := pkg.Analyser()
+
+	settings := Settings{}
+	if err := mapstructure.Decode(conf, &settings); err != nil {
+		return nil, err
+	}
+
+	if settings.Config != "" {
+		if err := a.Flags.Set("config", settings.Config); err != nil {
+			return nil, err
+		}
+	}
+
+	return []*analysis.Analyzer{a}, nil
+}