Expand ignore_empty into ignore to handle other semantics

proto/protovalidate/buf/validate/validate.proto

@@ -146,7 +146,7 @@ message FieldConstraints {
   // described as "serialized in the wire format," which follows the following rules:
   //
   // - the following "nullable" fields must be explicitly set to be considered present:
-  //   - singular message fields (may be their empty value)
+  //   - singular message fields (whose fields may be unpopulated/default values)
   //   - member fields of a oneof (may be their default value)
   //   - proto3 optional fields (may be their default value)
   //   - proto2 scalar fields
@@ -160,22 +160,22 @@ message FieldConstraints {
   // }
   // ```
   bool required = 25;
-  // If `ignore_empty` is true and applied to a non-nullable field (see
-  // `required` for more details), validation is skipped on the field if it is
-  // the default or empty value. Adding `ignore_empty` to a "nullable" field is
-  // a noop as these unset fields already skip validation (with the exception
-  // of `required`).
+  // DEPRECATED: use ignore=IGNORE_EMPTY instead.
+  bool ignore_empty = 26 [deprecated = true];
+  // Skip validation on the field if its value matches the specified rule.
   //
   // ```proto
-  // message MyRepeated {
-  //   // The field `value` min_len rule is only applied if the field isn't empty.
-  //   repeated string value = 1 [
-  //     (buf.validate.field).ignore_empty = true,
-  //     (buf.validate.field).min_len = 5
+  // message UpdateRequest {
+  //   // The uri rule only applies if the field is populated and not an empty
+  //   // string.
+  //   optional string url = 1 [
+  //     (buf.validate.field).ignore = IGNORE_DEFAULT,
+  //     (buf.validate.field).string.uri = true,
   //   ];
   // }
   // ```
-  bool ignore_empty = 26;
+  Ignore ignore = 27;
+
   oneof type {
     // Scalar Field Types
     FloatRules float = 1;
@@ -206,6 +206,19 @@ message FieldConstraints {
   }
 }
 
+// Specifies how FieldConstraints.ignore behaves. See the documentation for
+// FieldConstraints.required for definitions of "populated" and "nullable".
+enum Ignore {
+  // Validation is never skipped on the field unless it's an unpopulated
+  // nullable field.
+  IGNORE_UNSPECIFIED = 0;
+  // Validation is skipped if the field is unpopulated.
+  IGNORE_EMPTY = 1;
+  // Validation is skipped if the field is unpopulated or if it is a nullable
+  // field populated with its default value.
+  IGNORE_DEFAULT = 2;
+}
+
 // FloatRules describes the constraints applied to `float` values. These
 // rules may also be applied to the `google.protobuf.FloatValue` Well-Known-Type.
 message FloatRules {