Update PROTOVALIDATE lint rule to check unenforceable required rules (#4309)

These are unenforceable, because `repeated` and `map` fields do not
track field presence.

Ref: https://protovalidate.com/schemas/standard-rules/#field-presence

Fixes #3812.

Author: stefanvanburen

CHANGELOG.md

@@ -4,7 +4,8 @@
 
 - Add `buf registry policy {commit,create,delete,info,label,settings}` commands to manage BSR policies.
 - Add LSP deprecate code action to add the deprecated option on types and symbols.
-- Fix import LSP document link to not include `import` keyword
+- Fix import LSP document link to not include `import` keyword.
+- Update `PROTOVALIDATE` lint rule to support checking unenforceable `required` rules on `repeated.items`, `map.keys` and `map.values`.
 
 ## [v1.64.0] - 2026-01-19
 

private/bufpkg/bufcheck/bufcheckserver/internal/buflintvalidate/field.go

@@ -453,6 +453,15 @@ func checkRepeatedRules(
 		)
 	}
 	itemAdder := baseAdder.cloneWithNewBasePath(repeatedRulesFieldNumber, itemsFieldNumberInRepeatedRules)
+	if repeatedRules.Items != nil && repeatedRules.Items.GetRequired() {
+		itemAdder.addForPathf(
+			[]int32{requiredFieldNumber},
+			"Field %q has %s on repeated item rules, which is unenforceable. The %s constraint cannot be applied to individual items in a repeated field.",
+			baseAdder.fieldName(),
+			itemAdder.getFieldRuleName(requiredFieldNumber),
+			itemAdder.getFieldRuleName(requiredFieldNumber),
+		)
+	}
 	return checkRulesForField(itemAdder, repeatedRules.Items, containingMessageDescriptor, nil, fieldDescriptor, false, extensionTypeResolver)
 }
 
@@ -493,11 +502,29 @@ func checkMapRules(
 		)
 	}
 	keyAdder := baseAdder.cloneWithNewBasePath(mapRulesFieldNumber, keysFieldNumberInMapRules)
+	if mapRules.Keys != nil && mapRules.Keys.GetRequired() {
+		keyAdder.addForPathf(
+			[]int32{requiredFieldNumber},
+			"Field %q has %s on map key rules, which is unenforceable. The %s constraint cannot be applied to map keys.",
+			baseAdder.fieldName(),
+			keyAdder.getFieldRuleName(requiredFieldNumber),
+			keyAdder.getFieldRuleName(requiredFieldNumber),
+		)
+	}
 	err := checkRulesForField(keyAdder, mapRules.Keys, containingMessageDescriptor, fieldDescriptor, fieldDescriptor.MapKey(), false, extensionTypeResolver)
 	if err != nil {
 		return err
 	}
 	valueAdder := baseAdder.cloneWithNewBasePath(mapRulesFieldNumber, valuesFieldNumberInMapRules)
+	if mapRules.Values != nil && mapRules.Values.GetRequired() {
+		valueAdder.addForPathf(
+			[]int32{requiredFieldNumber},
+			"Field %q has %s on map value rules, which is unenforceable. The %s constraint cannot be applied to map values.",
+			baseAdder.fieldName(),
+			valueAdder.getFieldRuleName(requiredFieldNumber),
+			valueAdder.getFieldRuleName(requiredFieldNumber),
+		)
+	}
 	return checkRulesForField(valueAdder, mapRules.Values, containingMessageDescriptor, fieldDescriptor, fieldDescriptor.MapValue(), false, extensionTypeResolver)
 }
 

private/bufpkg/bufcheck/lint_test.go

@@ -682,6 +682,8 @@ func TestRunProtovalidate(t *testing.T) {
 		bufanalysistesting.NewFileAnnotation(t, "map.proto", 83, 5, 83, 55, "PROTOVALIDATE"),
 		bufanalysistesting.NewFileAnnotation(t, "map.proto", 86, 5, 86, 57, "PROTOVALIDATE"),
 		bufanalysistesting.NewFileAnnotation(t, "map.proto", 87, 5, 87, 55, "PROTOVALIDATE"),
+		bufanalysistesting.NewFileAnnotation(t, "map.proto", 90, 53, 90, 98, "PROTOVALIDATE"),
+		bufanalysistesting.NewFileAnnotation(t, "map.proto", 92, 55, 92, 102, "PROTOVALIDATE"),
 		bufanalysistesting.NewFileAnnotation(t, "number.proto", 20, 5, 20, 42, "PROTOVALIDATE"),
 		bufanalysistesting.NewFileAnnotation(t, "number.proto", 25, 5, 25, 43, "PROTOVALIDATE"),
 		bufanalysistesting.NewFileAnnotation(t, "number.proto", 28, 5, 28, 43, "PROTOVALIDATE"),
@@ -740,6 +742,7 @@ func TestRunProtovalidate(t *testing.T) {
 		bufanalysistesting.NewFileAnnotation(t, "repeated.proto", 55, 42, 55, 76, "PROTOVALIDATE"),
 		bufanalysistesting.NewFileAnnotation(t, "repeated.proto", 65, 5, 65, 62, "PROTOVALIDATE"),
 		bufanalysistesting.NewFileAnnotation(t, "repeated.proto", 68, 55, 68, 110, "PROTOVALIDATE"),
+		bufanalysistesting.NewFileAnnotation(t, "repeated.proto", 70, 51, 70, 102, "PROTOVALIDATE"),
 		bufanalysistesting.NewFileAnnotation(t, "string.proto", 31, 5, 31, 46, "PROTOVALIDATE"),
 		bufanalysistesting.NewFileAnnotation(t, "string.proto", 36, 5, 36, 44, "PROTOVALIDATE"),
 		bufanalysistesting.NewFileAnnotation(t, "string.proto", 41, 5, 41, 44, "PROTOVALIDATE"),

private/bufpkg/bufcheck/testdata/lint/protovalidate/proto/map.proto

@@ -86,4 +86,8 @@ message MapTest {
     (buf.validate.field).map.keys.string.example = "bad",
     (buf.validate.field).map.values.int64.example = -1
   ];
+  // invalid: required cannot be set on map keys
+  map<string, int32> invalid_required_on_keys = 19 [(buf.validate.field).map.keys.required = true];
+  // invalid: required cannot be set on map values
+  map<int32, string> invalid_required_on_values = 20 [(buf.validate.field).map.values.required = true];
 }

private/bufpkg/bufcheck/testdata/lint/protovalidate/proto/repeated.proto

@@ -66,4 +66,6 @@ message RepeatedTest {
   ];
   repeated string valid_no_constraint_example = 21 [(buf.validate.field).repeated.items.string.example = "proto"];
   repeated string invalid_no_constraint_example = 22 [(buf.validate.field).repeated.items.bool.example = true];
+  // invalid: required cannot be set on repeated items
+  repeated string invalid_required_on_items = 23 [(buf.validate.field).repeated.items.required = true];
 }