Add safety check for package list validation

pkg/merge/merge.go

@@ -1,9 +1,16 @@
 package merge
 
-func Merge(packages map[string]bool) []string {
+import "errors"
+
+var ErrEmptyList = errors.New("package list is empty")
+
+func Merge(packages map[string]bool) ([]string, error) {
 	result := make([]string, 0, len(packages))
 	for name := range packages {
 		result = append(result, name)
 	}
-	return result
+	if len(result) == 0 {
+		return nil, ErrEmptyList
+	}
+	return result, nil
 }

pkg/output/output.go

@@ -14,13 +14,13 @@ type Result struct {
 
 func Format(r *Result) string {
 	var b strings.Builder
-	b.WriteString(fmt.Sprintf("Installed %d packages, removed %d packages", r.Installed, r.Removed))
+	b.WriteString(fmt.Sprintf("installed %d packages, removed %d packages", r.Installed, r.Removed))
 	if len(r.ToInstall) > 0 {
-		b.WriteString("\nWould install: ")
+		b.WriteString("\nwould install: ")
 		b.WriteString(strings.Join(r.ToInstall, ", "))
 	}
 	if len(r.ToRemove) > 0 {
-		b.WriteString("\nWould remove: ")
+		b.WriteString("\nwould remove: ")
 		b.WriteString(strings.Join(r.ToRemove, ", "))
 	}
 	return b.String()

pkg/pacman/pacman.go

@@ -13,10 +13,21 @@ import (
 	"github.com/Riyyi/declpac/pkg/pacman/sync"
 )
 
-func Sync(packages []string) (*output.Result, error) {
+func Sync(packages []string, noCheck bool) (*output.Result, error) {
 	start := time.Now()
 	log.Debug("Sync: starting...")
 
+	explicitList, err := read.ExplicitList()
+	if err != nil {
+		return nil, err
+	}
+	explicitCount := len(explicitList)
+
+	if !noCheck && len(packages) < explicitCount/2 {
+		errMsg := "safety check: state packages (%d) less than half of explicitly installed (%d), override with --nocheck"
+		return nil, fmt.Errorf(errMsg, len(packages), explicitCount)
+	}
+
 	list, err := read.List()
 	if err != nil {
 		return nil, err

pkg/pacman/read/read.go

@@ -35,6 +35,25 @@ func List() ([]string, error) {
 	return list, nil
 }
 
+func ExplicitList() ([]string, error) {
+	start := time.Now()
+	log.Debug("ExplicitList: starting...")
+
+	cmd := exec.Command("pacman", "-Qqe")
+	output, err := cmd.Output()
+	if err != nil {
+		return nil, err
+	}
+
+	list := strings.Split(strings.TrimSpace(string(output)), "\n")
+	if len(list) > 0 && list[0] == "" {
+		list = nil
+	}
+
+	log.Debug("ExplicitList: done (%.2fs)", time.Since(start).Seconds())
+	return list, nil
+}
+
 func ListOrphans() ([]string, error) {
 	start := time.Now()
 	log.Debug("ListOrphans: starting...")