unexportedglobal: Linter to require '_' prefix on globals

This adds a unexportedglobal to golangci-lint.
[unexportedglobal][1] is a linter that requires that
unexported global variables and constants are prefixed with '_'.

  [1]: https://github.com/abhinav/unexportedglobal

```go
package foo

// Bad
var pool = sync.Pool{ /* ... */ }

// Good
var _pool = sync.Pool{ /* ... */ }
```

The idea is to eliminate the risk of conflict between
names of local variables and names of global variables.

The linter is inspired by the [Prefix Unexported Globals with `_`][2]
guidance in [Uber's Go Style Guide][3].

  [2]: https://github.com/uber-go/guide/blob/master/style.md#prefix-unexported-globals-with-_
  [3]: https://github.com/uber-go/guide/blob/master/style.md

The linter is not enabled by default.
I have also not added it to the 'style' preset
because not everyone may agree with this change.

Author: abhinav

.golangci.reference.yml

@@ -2175,6 +2175,7 @@ linters:
     - tparallel
     - typecheck
     - unconvert
+    - unexportedglobal
     - unparam
     - unused
     - usestdlibvars
@@ -2289,6 +2290,7 @@ linters:
     - tparallel
     - typecheck
     - unconvert
+    - unexportedglobal
     - unparam
     - unused
     - usestdlibvars

go.mod

@@ -115,9 +115,10 @@ require (
 	github.com/yeya24/promlinter v0.2.0
 	github.com/ykadowak/zerologlint v0.1.3
 	gitlab.com/bosi/decorder v0.2.3
+	go.abhg.dev/unexportedglobal v0.2.0
 	go.tmz.dev/musttag v0.7.1
 	golang.org/x/exp v0.0.0-20230510235704-dd950f8aeaea
-	golang.org/x/tools v0.10.0
+	golang.org/x/tools v0.11.0
 	gopkg.in/yaml.v3 v3.0.1
 	honnef.co/go/tools v0.4.3
 	mvdan.cc/gofumpt v0.5.0
@@ -185,9 +186,9 @@ require (
 	go.uber.org/multierr v1.6.0 // indirect
 	go.uber.org/zap v1.24.0 // indirect
 	golang.org/x/exp/typeparams v0.0.0-20230224173230-c95f2b4c22f2 // indirect
-	golang.org/x/mod v0.11.0 // indirect
+	golang.org/x/mod v0.12.0 // indirect
 	golang.org/x/sync v0.3.0 // indirect
-	golang.org/x/sys v0.9.0 // indirect
+	golang.org/x/sys v0.10.0 // indirect
 	golang.org/x/text v0.9.0 // indirect
 	google.golang.org/protobuf v1.28.0 // indirect
 	gopkg.in/ini.v1 v1.67.0 // indirect

go.sum

@@ -0,0 +1,16 @@
+package golinters
+
+import (
+	"github.com/golangci/golangci-lint/pkg/golinters/goanalysis"
+	"go.abhg.dev/unexportedglobal"
+	"golang.org/x/tools/go/analysis"
+)
+
+func NewUnexportedGlobal() *goanalysis.Linter {
+	return goanalysis.NewLinter(
+		"unexportedglobal",
+		"Disallows unexported globals without a '_' prefix",
+		[]*analysis.Analyzer{unexportedglobal.Analyzer},
+		nil,
+	).WithLoadMode(goanalysis.LoadModeTypesInfo)
+}

pkg/golinters/unexportedglobal.go

@@ -817,6 +817,13 @@ func (m Manager) GetAllSupportedLinterConfigs() []*linter.Config {
 			WithPresets(linter.PresetStyle).
 			WithURL("https://github.com/mdempsky/unconvert"),
 
+		linter.NewConfig(golinters.NewUnexportedGlobal()).
+			WithSince("v1.54.0").
+			WithLoadForGoAnalysis().
+			WithPresets(linter.PresetStyle).
+			WithAutoFix().
+			WithURL("https://github.com/abhinav/unexportedglobal"),
+
 		linter.NewConfig(golinters.NewUnparam(unparamCfg)).
 			WithSince("v1.9.0").
 			WithPresets(linter.PresetUnused).

pkg/lint/lintersdb/manager.go

@@ -0,0 +1,15 @@
+//golangcitest:args -Eunexportedglobal
+package testdata
+
+import "fmt"
+
+var ExportedVar = 1 // ok
+
+var unexportedVar = 1 // want `unexported global "unexportedVar" should be prefixed with '_'`
+
+var _unexportedVar = 1 // ok
+
+func _1() {
+	var local = 42
+	fmt.Println(local) // ok
+}