Fixes false negatives in unused dependency checker.

Don't mark a dependency as used just because it defines a package that's used, since many files can define the same package.

PiperOrigin-RevId: 533184254

src/google/protobuf/descriptor.cc

@@ -4436,7 +4436,7 @@ Symbol DescriptorBuilder::FindSymbolNotEnforcingDeps(const std::string& name,
   // Only find symbols which were defined in this file or one of its
   // dependencies.
   const FileDescriptor* file = result.GetFile();
-  if (file == file_ || dependencies_.contains(file)) {
+  if ((file == file_ || dependencies_.contains(file)) && !result.IsPackage()) {
     unused_dependency_.erase(file);
   }
   return result;

src/google/protobuf/descriptor_unittest.cc

@@ -6204,6 +6204,42 @@ TEST_F(ValidationErrorTest, UnusedImportWarning) {
       "forward.proto: bar.proto: IMPORT: Import bar.proto is unused.\n");
 }
 
+// Verifies that the dependency checker isn't fooled by package symbols,
+// which can be defined in multiple files.
+TEST_F(ValidationErrorTest, SamePackageUnusedImportError) {
+  BuildFile(R"pb(
+    name: "unused_dependency.proto"
+    package: "protobuf_unittest.subpackage"
+    message_type { name: "Foo" }
+  )pb");
+
+  BuildFile(R"pb(
+    name: "used_dependency.proto"
+    package: "protobuf_unittest.subpackage"
+    message_type { name: "Bar" }
+  )pb");
+
+  pool_.AddUnusedImportTrackFile("import.proto", true);
+  BuildFileWithErrors(R"pb(
+                        name: "import.proto"
+                        package: "protobuf_unittest"
+                        dependency: "unused_dependency.proto"
+                        dependency: "used_dependency.proto"
+                        message_type {
+                          name: "Baz"
+                          field {
+                            name: "bar"
+                            number: 1
+                            label: LABEL_OPTIONAL
+                            type: TYPE_MESSAGE
+                            type_name: "subpackage.Bar"
+                          }
+                        }
+                      )pb",
+                      "import.proto: unused_dependency.proto: "
+                      "IMPORT: Import unused_dependency.proto is unused.\n");
+}
+
 namespace {
 void FillValidMapEntry(FileDescriptorProto* file_proto) {
   ASSERT_TRUE(TextFormat::ParseFromString(