feat: add gochecksumtype linter

`gochecksumtype` is a linter that checks that type switches on "sum
types" in Go are exhaustive.

https://github.com/alecthomas/go-check-sumtype

This is based on BurntSushi/go-sumtype, but fixes, modernises and
simplifies it.

Author: alecthomas

.golangci.reference.yml

@@ -2027,6 +2027,7 @@ linters:
     - gocheckcompilerdirectives
     - gochecknoglobals
     - gochecknoinits
+    - gochecksumtype
     - gocognit
     - goconst
     - gocritic
@@ -2137,6 +2138,7 @@ linters:
     - gocheckcompilerdirectives
     - gochecknoglobals
     - gochecknoinits
+    - gochecksumtype
     - gocognit
     - goconst
     - gocritic

go.mod

@@ -119,6 +119,7 @@ require (
 
 require (
 	github.com/Masterminds/semver v1.5.0 // indirect
+	github.com/alecthomas/go-check-sumtype v0.1.3
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.1.2 // indirect
 	github.com/chavacava/garif v0.0.0-20221024190013-b3ef35877348 // indirect

go.sum

@@ -0,0 +1,73 @@
+package golinters
+
+import (
+	"strings"
+	"sync"
+
+	gochecksumtype "github.com/alecthomas/go-check-sumtype"
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/go/packages"
+
+	"github.com/golangci/golangci-lint/pkg/golinters/goanalysis"
+	"github.com/golangci/golangci-lint/pkg/lint/linter"
+	"github.com/golangci/golangci-lint/pkg/result"
+)
+
+const goCheckSumTypeName = "gochecksumtype"
+
+func NewGoCheckSumType() *goanalysis.Linter {
+	var mu sync.Mutex
+	var resIssues []goanalysis.Issue
+
+	analyzer := &analysis.Analyzer{
+		Name: goCheckSumTypeName,
+		Doc:  goanalysis.TheOnlyanalyzerDoc,
+		Run: func(pass *analysis.Pass) (interface{}, error) {
+			issues, err := runGoCheckSumType(pass)
+			if err != nil {
+				return nil, err
+			}
+			if len(issues) == 0 {
+				return nil, nil
+			}
+			mu.Lock()
+			resIssues = append(resIssues, issues...)
+			mu.Unlock()
+			return nil, nil
+		},
+	}
+	return goanalysis.NewLinter(
+		goCheckSumTypeName,
+		`Run exhaustiveness checks on Go "sum types"`,
+		[]*analysis.Analyzer{analyzer},
+		nil,
+	).WithIssuesReporter(func(ctx *linter.Context) []goanalysis.Issue {
+		return resIssues
+	}).WithLoadMode(goanalysis.LoadModeTypesInfo)
+}
+
+func runGoCheckSumType(pass *analysis.Pass) ([]goanalysis.Issue, error) {
+	resIssues := []goanalysis.Issue{}
+	pkg := &packages.Package{
+		Fset:      pass.Fset,
+		Syntax:    pass.Files,
+		Types:     pass.Pkg,
+		TypesInfo: pass.TypesInfo,
+	}
+	var unknownError error
+	errors := gochecksumtype.Run([]*packages.Package{pkg})
+	for _, err := range errors {
+		err, ok := err.(gochecksumtype.Error)
+		if !ok {
+			unknownError = err
+			continue
+		}
+		prefix := err.Pos().String() + ": "
+		resIssues = append(resIssues, goanalysis.NewIssue(&result.Issue{
+			FromLinter: goCheckSumTypeName,
+			Text:       strings.TrimPrefix(err.Error(), prefix),
+			Pos:        err.Pos(),
+		}, pass))
+	}
+	return resIssues, unknownError
+}

pkg/golinters/gochecksumtype.go

@@ -37,7 +37,6 @@ func NewUnparam(settings *config.UnparamSettings) *goanalysis.Linter {
 			mu.Lock()
 			resIssues = append(resIssues, issues...)
 			mu.Unlock()
-
 			return nil, nil
 		},
 	}

pkg/golinters/unparam.go

@@ -456,6 +456,11 @@ func (m Manager) GetAllSupportedLinterConfigs() []*linter.Config {
 			WithSince("v1.12.0").
 			WithPresets(linter.PresetStyle),
 
+		linter.NewConfig(golinters.NewGoCheckSumType()).
+			WithSince("v1.51.2").
+			WithPresets(linter.PresetBugs).
+			WithURL("https://github.com/alecthomas/go-check-sumtype"),
+
 		linter.NewConfig(golinters.NewGocognit(gocognitCfg)).
 			WithSince("v1.20.0").
 			WithPresets(linter.PresetComplexity).

pkg/lint/lintersdb/manager.go

@@ -0,0 +1,32 @@
+//golangcitest:args -Egochecksumtype
+package testdata
+
+//sumtype:decl
+type SumType interface{ isSumType() }
+
+//sumtype:decl
+type One struct{} // want "type 'One' is not an interface"
+
+func (One) isSumType() {}
+
+type Two struct{}
+
+func (Two) isSumType() {}
+
+func sumTypeTest() {
+	var sum SumType = One{}
+	switch sum.(type) { // want "exhaustiveness check failed for sum type.*SumType.*missing cases for Two"
+	case One:
+	}
+
+	switch sum.(type) { // want "exhaustiveness check failed for sum type.*SumType.*missing cases for Two"
+	case One:
+	default:
+		panic("??")
+	}
+
+	switch sum.(type) {
+	case One:
+	case Two:
+	}
+}