add coordinate set

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

syft/source/coordinates.go

@@ -2,6 +2,7 @@ package source
 
 import (
 	"fmt"
+	"sort"
 
 	"github.com/anchore/syft/internal/log"
 	"github.com/anchore/syft/syft/artifact"
@@ -13,6 +14,18 @@ type Coordinates struct {
 	FileSystemID string `json:"layerID,omitempty"` // An ID representing the filesystem. For container images, this is a layer digest. For directories or a root filesystem, this is blank.
 }
 
+// CoordinateSet represents a set of string types.
+type CoordinateSet map[Coordinates]struct{}
+
+// NewCoordinateSet creates a CoordinateSet populated with values from the given slice.
+func NewCoordinateSet(start ...Coordinates) CoordinateSet {
+	ret := make(CoordinateSet)
+	for _, s := range start {
+		ret.Add(s)
+	}
+	return ret
+}
+
 func (c Coordinates) ID() artifact.ID {
 	f, err := artifact.IDFromHash(c)
 	if err != nil {
@@ -32,3 +45,37 @@ func (c Coordinates) String() string {
 	}
 	return fmt.Sprintf("Location<%s>", str)
 }
+
+// Add a string to the set.
+func (s CoordinateSet) Add(i Coordinates) {
+	s[i] = struct{}{}
+}
+
+// Remove a string from the set.
+func (s CoordinateSet) Remove(i Coordinates) {
+	delete(s, i)
+}
+
+// Contains indicates if the given string is contained within the set.
+func (s CoordinateSet) Contains(i Coordinates) bool {
+	_, ok := s[i]
+	return ok
+}
+
+// ToSlice returns a sorted slice of Locations that are contained within the set.
+func (s CoordinateSet) ToSlice() []Coordinates {
+	ret := make([]Coordinates, len(s))
+	idx := 0
+	for v := range s {
+		ret[idx] = v
+		idx++
+	}
+
+	sort.SliceStable(ret, func(i, j int) bool {
+		if ret[i].RealPath == ret[j].RealPath {
+			return ret[i].FileSystemID < ret[j].FileSystemID
+		}
+		return ret[i].RealPath < ret[j].RealPath
+	})
+	return ret
+}