fix(coderd/util/maps): ignore zero values in Subset

johnstcn · johnstcn · commit 795ffda6669f · 2025-02-10T18:00:04.000Z
diff --git a/coderd/util/maps/maps.go b/coderd/util/maps/maps.go
@@ -8,9 +8,14 @@ import (
 
 // Subset returns true if all the keys of a are present
 // in b and have the same values.
+// If the corresponding value of a[k] is the zero value in
+// b, Subset will skip comparing that value.
+// This allows checking for the presence of map keys.
 func Subset[T, U comparable](a, b map[T]U) bool {
+	var uz U
 	for ka, va := range a {
-		if vb, ok := b[ka]; !ok || va != vb {
+		ignoreZeroValue := va == uz
+		if vb, ok := b[ka]; !ok || (!ignoreZeroValue && va != vb) {
 			return false
 		}
 	}
diff --git a/coderd/util/maps/maps_test.go b/coderd/util/maps/maps_test.go
@@ -11,8 +11,9 @@ func TestSubset(t *testing.T) {
 	t.Parallel()
 
 	for idx, tc := range []struct {
-		a        map[string]string
-		b        map[string]string
+		a map[string]string
+		b map[string]string
+		// expected value from Subset
 		expected bool
 	}{
 		{
@@ -50,6 +51,24 @@ func TestSubset(t *testing.T) {
 			b:        map[string]string{"a": "1", "b": "3"},
 			expected: false,
 		},
+		// Zero value
+		{
+			a:        map[string]string{"a": "1", "b": ""},
+			b:        map[string]string{"a": "1", "b": "3"},
+			expected: true,
+		},
+		// Zero value, but the other way round
+		{
+			a:        map[string]string{"a": "1", "b": "3"},
+			b:        map[string]string{"a": "1", "b": ""},
+			expected: false,
+		},
+		// Both zero values
+		{
+			a:        map[string]string{"a": "1", "b": ""},
+			b:        map[string]string{"a": "1", "b": ""},
+			expected: true,
+		},
 	} {
 		tc := tc
 		t.Run("#"+strconv.Itoa(idx), func(t *testing.T) {
