feat: add gomod package

Author: ldez

gomod/gomod.go

@@ -0,0 +1,57 @@
+// Package gomod A function to get information about module (go list).
+package gomod
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os/exec"
+)
+
+// ModInfo Module information.
+//
+//nolint:tagliatelle // temporary: the next version of golangci-lint will allow configuration by package.
+type ModInfo struct {
+	Path      string `json:"Path"`
+	Dir       string `json:"Dir"`
+	GoMod     string `json:"GoMod"`
+	GoVersion string `json:"GoVersion"`
+	Main      bool   `json:"Main"`
+}
+
+// GetModuleInfo gets modules information from `go list`.
+func GetModuleInfo() ([]ModInfo, error) {
+	// https://github.com/golang/go/issues/44753#issuecomment-790089020
+	cmd := exec.Command("go", "list", "-m", "-json")
+
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, fmt.Errorf("command go list: %w: %s", err, string(out))
+	}
+
+	var infos []ModInfo
+
+	for dec := json.NewDecoder(bytes.NewBuffer(out)); dec.More(); {
+		var v ModInfo
+		if err := dec.Decode(&v); err != nil {
+			return nil, fmt.Errorf("unmarshaling error: %w: %s", err, string(out))
+		}
+
+		if v.GoMod == "" {
+			return nil, errors.New("working directory is not part of a module")
+		}
+
+		if !v.Main || v.Dir == "" {
+			continue
+		}
+
+		infos = append(infos, v)
+	}
+
+	if len(infos) == 0 {
+		return nil, errors.New("go.mod file not found")
+	}
+
+	return infos, nil
+}