gofumpt: Add lang-version option + update linter

Without the Go language version input, `gofumpt` cannot apply some rules
which are version dependent.

Defaulting `lang-version` to the Go version of the running environment
if not specified.

Signed-off-by: Kailun Qin <[email protected]>

Author: kailun-qin

.golangci.example.yml

@@ -259,6 +259,10 @@ linters-settings:
     simplify: true
 
   gofumpt:
+    # Select the Go language version to target.
+    # Default is the Go version installed in the running environment.
+    lang-version: "1.15"
+
     # Choose whether or not to use the extra rules that are disabled
     # by default
     extra-rules: false

pkg/config/linters_settings.go

@@ -59,7 +59,8 @@ var defaultLintersSettings = LintersSettings{
 		DefaultSignifiesExhaustive: false,
 	},
 	Gofumpt: GofumptSettings{
-		ExtraRules: false,
+		LangVersion: "",
+		ExtraRules:  false,
 	},
 	ErrorLint: ErrorLintSettings{
 		Errorf:     true,
@@ -232,7 +233,8 @@ type GoFmtSettings struct {
 }
 
 type GofumptSettings struct {
-	ExtraRules bool `mapstructure:"extra-rules"`
+	LangVersion string `mapstructure:"lang-version"`
+	ExtraRules  bool   `mapstructure:"extra-rules"`
 }
 
 type GoHeaderSettings struct {

pkg/golinters/gofumpt.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"io/ioutil"
+	"os/exec"
 	"sync"
 
 	"github.com/pkg/errors"
@@ -33,6 +34,24 @@ func NewGofumpt() *goanalysis.Linter {
 		nil,
 	).WithContextSetter(func(lintCtx *linter.Context) {
 		analyzer.Run = func(pass *analysis.Pass) (interface{}, error) {
+			settings := lintCtx.Settings().Gofumpt
+
+			// Get the target Go language version to be used in gofumpt.
+			// Reuse logic from `https://github.com/mvdan/gofumpt/blob/ba6406b58f3630c5246474b20f6ee5c83d1cc6b9/gofmt.go#L127-L133`.
+			langVersion := settings.LangVersion
+			if langVersion == "" {
+				outGoVersion, errGoVersion := exec.Command("go", "list", "-m", "-f", "{{.GoVersion}}").Output()
+				outGoVersion = bytes.TrimSpace(outGoVersion)
+				if errGoVersion == nil && len(outGoVersion) > 0 {
+					langVersion = string(outGoVersion)
+				}
+			}
+
+			options := format.Options{
+				LangVersion: langVersion,
+				ExtraRules:  settings.ExtraRules,
+			}
+
 			var fileNames []string
 			for _, f := range pass.Files {
 				pos := pass.Fset.PositionFor(f.Pos(), false)
@@ -46,12 +65,12 @@ func NewGofumpt() *goanalysis.Linter {
 				if err != nil {
 					return nil, fmt.Errorf("unable to open file %s: %w", f, err)
 				}
-				output, err := format.Source(input, format.Options{
-					ExtraRules: lintCtx.Settings().Gofumpt.ExtraRules,
-				})
+
+				output, err := format.Source(input, options)
 				if err != nil {
 					return nil, fmt.Errorf("error while running gofumpt: %w", err)
 				}
+
 				if !bytes.Equal(input, output) {
 					out := bytes.Buffer{}
 					_, err = out.WriteString(fmt.Sprintf("--- %[1]s\n+++ %[1]s\n", f))