absolute: efficient equivalence check method

This is more efficient and makes the call site cleaner.

Signed-off-by: Ophestra <cat@gensokyo.uk>

container/absolute.go

@@ -39,6 +39,15 @@ func (a *Absolute) String() string {
 	return a.pathname
 }
 
+func (a *Absolute) Is(v *Absolute) bool {
+	if a == nil && v == nil {
+		return true
+	}
+	return a != nil && v != nil &&
+		a.pathname != zeroString && v.pathname != zeroString &&
+		a.pathname == v.pathname
+}
+
 // NewAbs checks pathname and returns a new [Absolute] if pathname is absolute.
 func NewAbs(pathname string) (*Absolute, error) {
 	if !isAbs(pathname) {

container/absolute_test.go

@@ -69,7 +69,7 @@ func TestNewAbs(t *testing.T) {
 			wantPanic := `path "etc" is not absolute`
 
 			if r := recover(); r != wantPanic {
-				t.Errorf("MustAbsolute: panic = %v; want %v", r, wantPanic)
+				t.Errorf("MustAbs: panic = %v; want %v", r, wantPanic)
 			}
 		}()
 
@@ -98,6 +98,29 @@ func TestAbsoluteString(t *testing.T) {
 	})
 }
 
+func TestAbsoluteIs(t *testing.T) {
+	testCases := []struct {
+		name string
+		a, v *Absolute
+		want bool
+	}{
+		{"nil", (*Absolute)(nil), (*Absolute)(nil), true},
+		{"nil a", (*Absolute)(nil), MustAbs("/"), false},
+		{"nil v", MustAbs("/"), (*Absolute)(nil), false},
+		{"zero", new(Absolute), new(Absolute), false},
+		{"zero a", new(Absolute), MustAbs("/"), false},
+		{"zero v", MustAbs("/"), new(Absolute), false},
+		{"equals", MustAbs("/"), MustAbs("/"), true},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := tc.a.Is(tc.v); got != tc.want {
+				t.Errorf("Is: %v, want %v", got, tc.want)
+			}
+		})
+	}
+}
+
 type sCheck struct {
 	Pathname *Absolute `json:"val"`
 	Magic    int       `json:"magic"`