add skills command scaffold

internal/skills/collisions.go

@@ -0,0 +1,55 @@
+package skills
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/cli/cli/v2/internal/skills/discovery"
+)
+
+// NameCollision represents a group of skills that share the same InstallName
+// and would overwrite each other when installed to the same directory.
+type NameCollision struct {
+	Name         string   // the conflicting install name (may include namespace prefix)
+	DisplayNames []string // display names of each conflicting skill
+}
+
+// FindNameCollisions detects skills that share the same InstallName and returns a
+// sorted slice of collisions. Callers decide how to present the conflict to
+// the user (different flows need different error messages).
+func FindNameCollisions(skills []discovery.Skill) []NameCollision {
+	byName := make(map[string][]discovery.Skill)
+	for _, s := range skills {
+		byName[s.InstallName()] = append(byName[s.InstallName()], s)
+	}
+
+	var collisions []NameCollision
+	for name, group := range byName {
+		if len(group) <= 1 {
+			continue
+		}
+		names := make([]string, len(group))
+		for i, s := range group {
+			names[i] = s.DisplayName()
+		}
+		collisions = append(collisions, NameCollision{Name: name, DisplayNames: names})
+	}
+
+	sort.Slice(collisions, func(i, j int) bool {
+		return collisions[i].Name < collisions[j].Name
+	})
+	return collisions
+}
+
+// FormatCollisions builds a human-readable string listing each collision,
+// suitable for embedding in an error message. Each collision is formatted as
+// "name: display1, display2" and collisions are separated by newlines with
+// leading indentation.
+func FormatCollisions(collisions []NameCollision) string {
+	lines := make([]string, len(collisions))
+	for i, c := range collisions {
+		lines[i] = fmt.Sprintf("%s: %s", c.Name, strings.Join(c.DisplayNames, ", "))
+	}
+	return strings.Join(lines, "\n  ")
+}