validation-gen/util: add ParseInt utility for canonical integer parsing

Signed-off-by: Bryce Palmer <bpalmer@redhat.com>

staging/src/k8s.io/code-generator/cmd/validation-gen/util/util.go

@@ -17,6 +17,9 @@ limitations under the License.
 package util
 
 import (
+	"fmt"
+	"strconv"
+
 	"k8s.io/gengo/v2/parser/tags"
 	"k8s.io/gengo/v2/types"
 )
@@ -114,3 +117,23 @@ func IsDirectComparable(t *types.Type) bool {
 	}
 	return false
 }
+
+// ParseInt strictly parses an int from a string input,
+// ensuring that when converted back to a string, the resulting
+// int and the input string have the exact same representation.
+// This prevents scenarios where an input like `0100` parses
+// as 100 and would be re-stringed as `100`.
+func ParseInt(val string) (int, error) {
+	intVal, err := strconv.Atoi(val)
+	if err != nil {
+		return 0, fmt.Errorf("parsing %q as int: %w", val, err)
+	}
+
+	strVal := strconv.Itoa(intVal)
+	if strVal != val {
+		err := fmt.Errorf("parsed int %d converted to a string value of %q which does not match the input string", intVal, strVal)
+		return 0, fmt.Errorf("parsing %q as int: %w", val, err)
+	}
+
+	return intVal, nil
+}

staging/src/k8s.io/code-generator/cmd/validation-gen/util/util_test.go

@@ -452,3 +452,55 @@ func TestIsDirectComparable(t *testing.T) {
 		}
 	}
 }
+
+func TestParseInt(t *testing.T) {
+	type testcase struct {
+		name          string
+		in            string
+		expectedOut   int
+		expectedError bool
+	}
+
+	testcases := []testcase{
+		{
+			name:          "valid canonical integer string",
+			in:            "100",
+			expectedOut:   100,
+			expectedError: false,
+		},
+		{
+			name:          "invalid canonical integer string, not an integer at all",
+			in:            "notanint",
+			expectedOut:   0,
+			expectedError: true,
+		},
+		{
+			name:          "invalid canonical integer string, spurious leading zeros",
+			in:            "00100",
+			expectedOut:   0,
+			expectedError: true,
+		},
+		{
+			name:          "invalid canonical integer string, octal value",
+			in:            "0o123",
+			expectedOut:   0,
+			expectedError: true,
+		},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			out, err := ParseInt(tc.in)
+			switch {
+			case tc.expectedError && err == nil:
+				t.Error("expected an error but did not receive one")
+			case !tc.expectedError && err != nil:
+				t.Errorf("received an unexpected error: %v", err)
+			}
+
+			if out != tc.expectedOut {
+				t.Errorf("expected an output value of %d but got %d", tc.expectedOut, out)
+			}
+		})
+	}
+}