Add a new util to clear a property

proptools.Clear(ptr) clears a property with its zero value.

Bug: 313806237
Test: m blueprint_tests
Change-Id: Ib78f9f88a9b0a8b04e1ab6c5e545b55ba4269e5d

proptools/proptools.go

@@ -53,6 +53,12 @@ func FieldNameForProperty(propertyName string) string {
 	return fieldName
 }
 
+// Clear takes a pointer to a field and clears the value pointed to by the pointer with zero value.
+func Clear[T any](ptr *T) {
+	var zeroValue T
+	*ptr = zeroValue
+}
+
 // BoolPtr returns a pointer to a new bool containing the given value.
 func BoolPtr(b bool) *bool {
 	return &b

proptools/proptools_test.go

@@ -14,7 +14,9 @@
 
 package proptools
 
-import "testing"
+import (
+	"testing"
+)
 
 func TestPropertyNameForField(t *testing.T) {
 	tests := []struct {
@@ -112,3 +114,45 @@ func TestFieldNameForProperty(t *testing.T) {
 		})
 	}
 }
+
+func TestClearField(t *testing.T) {
+	props := struct {
+		i  int
+		s  string
+		ps *string
+		ss []string
+		c  struct {
+			n int
+		}
+	}{}
+
+	props.i = 42
+	Clear(&props.i)
+	if props.i != 0 {
+		t.Error("int field is not cleared to zero.")
+	}
+
+	props.s = "foo"
+	Clear(&props.s)
+	if props.s != "" {
+		t.Error("string field is not cleared to zero.")
+	}
+
+	props.ps = StringPtr("foo")
+	Clear(&props.ps)
+	if props.ps != nil {
+		t.Error("string pointer field is not cleared to zero.")
+	}
+
+	props.ss = []string{"foo"}
+	Clear(&props.ss)
+	if props.ss != nil {
+		t.Error("string array field is not cleared to zero.")
+	}
+
+	props.c.n = 42
+	Clear(&props.c)
+	if props.c.n != 0 {
+		t.Error("struct field is not cleared to zero.")
+	}
+}