refactor: use go mod edit to get the main module (#72)

utils.go

@@ -2,57 +2,29 @@ package musttag
 
 import (
 	"encoding/json"
-	"errors"
 	"fmt"
-	"io"
-	"os"
 	"os/exec"
 	"strings"
 )
 
-var (
-	getwd         = os.Getwd
-	commandOutput = func(name string, args ...string) (string, error) {
-		output, err := exec.Command(name, args...).Output()
-		return string(output), err
-	}
-)
-
 func getMainModule() (string, error) {
-	args := []string{"go", "list", "-m", "-json"}
+	args := [...]string{"go", "mod", "edit", "-json"}
 
-	output, err := commandOutput(args[0], args[1:]...)
+	out, err := exec.Command(args[0], args[1:]...).Output()
 	if err != nil {
-		return "", fmt.Errorf("running `%s`: %w", strings.Join(args, " "), err)
+		return "", fmt.Errorf("running %q: %w", strings.Join(args[:], " "), err)
 	}
 
-	cwd, err := getwd()
-	if err != nil {
-		return "", fmt.Errorf("getting wd: %w", err)
+	var info struct {
+		Module struct {
+			Path string `json:"Path"`
+		} `json:"Module"`
 	}
-
-	decoder := json.NewDecoder(strings.NewReader(output))
-
-	for {
-		// multiple JSON objects will be returned when using Go workspaces; see #63 for details.
-		var module struct {
-			Path      string `json:"Path"`
-			Main      bool   `json:"Main"`
-			Dir       string `json:"Dir"`
-			GoMod     string `json:"GoMod"`
-			GoVersion string `json:"GoVersion"`
-		}
-		if err := decoder.Decode(&module); err != nil {
-			if errors.Is(err, io.EOF) {
-				return "", fmt.Errorf("main module not found\n%s", output)
-			}
-			return "", fmt.Errorf("decoding json: %w\n%s", err, output)
-		}
-
-		if module.Main && strings.HasPrefix(cwd, module.Dir) {
-			return module.Path, nil
-		}
+	if err := json.Unmarshal(out, &info); err != nil {
+		return "", fmt.Errorf("decoding module info: %w\n%s", err, out)
 	}
+
+	return info.Module.Path, nil
 }
 
 // based on golang.org/x/tools/imports.VendorlessPath

utils_test.go

@@ -7,42 +7,6 @@ import (
 	. "go-simpler.org/assert/EF"
 )
 
-func Test_getMainModule(t *testing.T) {
-	tests := map[string]struct {
-		want, output string
-	}{
-		"single module": {
-			want: "module1",
-			output: `
-{"Path": "module1", "Main": true, "Dir": "/path/to/module1"}`,
-		},
-		"multiple modules": {
-			want: "module1",
-			output: `
-{"Path": "module1", "Main": true, "Dir": "/path/to/module1"}
-{"Path": "module2", "Main": true, "Dir": "/path/to/module2"}`,
-		},
-	}
-
-	for name, test := range tests {
-		t.Run(name, func(t *testing.T) {
-			gwd, co := getwd, commandOutput
-			defer func() { getwd, commandOutput = gwd, co }()
-
-			getwd = func() (string, error) {
-				return "/path/to/module1/pkg", nil
-			}
-			commandOutput = func(string, ...string) (string, error) {
-				return test.output, nil
-			}
-
-			got, err := getMainModule()
-			assert.NoErr[F](t, err)
-			assert.Equal[E](t, got, test.want)
-		})
-	}
-}
-
 func Test_cutVendor(t *testing.T) {
 	tests := []struct {
 		path, want string