Add some java plugin integration tests.

PiperOrigin-RevId: 689943588

src/google/protobuf/compiler/java/BUILD.bazel

@@ -129,6 +129,7 @@ cc_library(
     deps = [
         ":generator_common",
         ":helpers",
+        ":internal_helpers",
         ":java_features_bootstrap",
         ":names",
         "//src/google/protobuf",
@@ -194,6 +195,20 @@ cc_library(
     ],
 )
 
+cc_test(
+    name = "generator_unittest",
+    srcs = ["generator_unittest.cc"],
+    deps = [
+        ":java",
+        ":java_features_bootstrap",
+        "//:protobuf",
+        "//src/google/protobuf",
+        "//src/google/protobuf/compiler:command_line_interface_tester",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_test(
     name = "doc_comment_unittest",
     srcs = ["doc_comment_unittest.cc"],

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

@@ -26,6 +26,7 @@
 #include "google/protobuf/compiler/java/generator_factory.h"
 #include "google/protobuf/compiler/java/helpers.h"
 #include "google/protobuf/compiler/java/full/generator_factory.h"
+#include "google/protobuf/compiler/java/internal_helpers.h"
 #include "google/protobuf/compiler/java/lite/generator_factory.h"
 #include "google/protobuf/compiler/java/name_resolver.h"
 #include "google/protobuf/compiler/java/options.h"
@@ -33,6 +34,7 @@
 #include "google/protobuf/compiler/retention.h"
 #include "google/protobuf/compiler/versions.h"
 #include "google/protobuf/descriptor.pb.h"
+#include "google/protobuf/descriptor_visitor.h"
 #include "google/protobuf/dynamic_message.h"
 #include "google/protobuf/io/printer.h"
 #include "google/protobuf/io/zero_copy_stream.h"
@@ -250,7 +252,8 @@ bool FileGenerator::Validate(std::string* error) {
            "https://github.com/protocolbuffers/protobuf/blob/main/java/"
            "lite.md";
   }
-  return true;
+
+  return error->empty();
 }
 
 void FileGenerator::Generate(io::Printer* printer) {

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

@@ -0,0 +1,72 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2023 Google Inc.  All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+#include "google/protobuf/compiler/java/generator.h"
+
+#include <memory>
+
+#include "google/protobuf/descriptor.pb.h"
+#include <gtest/gtest.h>
+#include "google/protobuf/compiler/java/java_features.pb.h"
+#include "google/protobuf/compiler/command_line_interface_tester.h"
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace java {
+namespace {
+
+class JavaGeneratorTest : public CommandLineInterfaceTester {
+ protected:
+  JavaGeneratorTest() {
+    RegisterGenerator("--java_out", "--java_opt",
+                      std::make_unique<JavaGenerator>(), "Java test generator");
+
+    // Generate built-in protos.
+    CreateTempFile(
+        "google/protobuf/descriptor.proto",
+        google::protobuf::DescriptorProto::descriptor()->file()->DebugString());
+    CreateTempFile("third_party/java/protobuf/java_features.proto",
+                   pb::JavaFeatures::descriptor()->file()->DebugString());
+  }
+};
+
+TEST_F(JavaGeneratorTest, Basic) {
+  CreateTempFile("foo.proto",
+                 R"schema(
+    syntax = "proto2";
+    message Foo {
+      optional int32 bar = 1;
+    })schema");
+
+  RunProtoc(
+      "protocol_compiler --proto_path=$tmpdir --java_out=$tmpdir foo.proto");
+
+  ExpectNoErrors();
+}
+
+TEST_F(JavaGeneratorTest, BasicError) {
+  CreateTempFile("foo.proto",
+                 R"schema(
+    syntax = "proto2";
+    message Foo {
+      int32 bar = 1;
+    })schema");
+
+  RunProtoc(
+      "protocol_compiler --proto_path=$tmpdir --java_out=$tmpdir foo.proto");
+
+  ExpectErrorSubstring(
+      "foo.proto:4:7: Expected \"required\", \"optional\", or \"repeated\"");
+}
+
+
+}  // namespace
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google