toolkit: convert WFN.Value to value receiver

When using the go sql driver WFN will not be recognized as a
driver.Valuer (only *WFN). As WFN is direct value in claircore's structs
this makes it fiddly, the change allows both pointer and value to
benefit from Value().

Signed-off-by: crozzy <[email protected]>

toolkit/types/cpe/marshaling.go

@@ -50,7 +50,7 @@ func (w *WFN) Scan(src interface{}) (err error) {
 }
 
 // Value implements [driver.Valuer].
-func (w *WFN) Value() (driver.Value, error) {
+func (w WFN) Value() (driver.Value, error) {
 	switch err := w.Valid(); {
 	case err == nil:
 	case errors.Is(err, ErrUnset):

toolkit/types/cpe/marshaling_test.go

@@ -1,11 +1,50 @@
 package cpe
 
 import (
+	"database/sql/driver"
+	"fmt"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
 )
 
+func TestConvertValue(t *testing.T) {
+	w := MustUnbind(`cpe:2.3:a:foo\\bar:big\$money:2010:*:*:*:special:ipod_touch:80gb:*`)
+	var testcases = []struct {
+		name    string
+		wfn     any
+		want    string
+		wantErr error
+	}{
+		{
+			name:    "test value",
+			wfn:     w,
+			want:    `cpe:2.3:a:foo\\bar:big\$money:2010:*:*:*:special:ipod_touch:80gb:*`,
+			wantErr: nil,
+		},
+		{
+			name:    "test pointer",
+			wfn:     &w,
+			want:    `cpe:2.3:a:foo\\bar:big\$money:2010:*:*:*:special:ipod_touch:80gb:*`,
+			wantErr: nil,
+		},
+	}
+	dpc := driver.DefaultParameterConverter
+	for _, tt := range testcases {
+		t.Run(tt.name, func(t *testing.T) {
+			val, err := dpc.ConvertValue(tt.wfn)
+			if err != tt.wantErr {
+				t.Fatal(err)
+			}
+			v := val.(string)
+			if v != tt.want {
+				t.Fatalf("wanted %q but got %q", tt.want, v)
+			}
+			fmt.Println()
+		})
+	}
+}
+
 func TestMarshal(t *testing.T) {
 	t.Parallel()
 	var names = []string{