Explicitly reject fields that are closed enums with implicit presence…

… in Java generators.

The normal case of this is already rejected by the .proto parser, this additional check covers legacy_closed_enum cases. Those cases will otherwise reach a CHECK-fail, this just makes for a clearer error message that this is simply a disallowed combination.

PiperOrigin-RevId: 696587446

src/google/protobuf/compiler/java/generator_unittest.cc

@@ -65,6 +65,28 @@ TEST_F(JavaGeneratorTest, BasicError) {
       "foo.proto:4:7: Expected \"required\", \"optional\", or \"repeated\"");
 }
 
+TEST_F(JavaGeneratorTest, ImplicitPresenceLegacyClosedEnumDisallowed) {
+  CreateTempFile("foo.proto",
+                 R"schema(
+    edition = "2023";
+    import "third_party/java/protobuf/java_features.proto";
+    option features.field_presence = IMPLICIT;
+    enum Bar {
+      AAA = 0;
+    }
+    message Foo {
+      Bar bar = 1 [features.(pb.java).legacy_closed_enum = true];
+    }
+  )schema");
+
+  RunProtoc(
+      "protocol_compiler --proto_path=$tmpdir --java_out=$tmpdir foo.proto");
+
+  ExpectErrorSubstring(
+      "foo.proto: Field Foo.bar has a closed enum type with implicit "
+      "presence.");
+}
+
 
 }  // namespace
 }  // namespace java