dart:mirrors fails to find metadata on dependencies

[sestegra]

Dart VM version: 2.0.0-dev.67.0 (Tue Jul 3 18:17:07 2018 +0200) on "macos_x64"

@Foo()
import 'dart:mirrors';

class Foo {
  const Foo();
}

@Foo()
class Bar {
  @Foo()
  String it;

  void doIt(@Foo() String param) {}
}

void main() {
  {
    print("### Annotation on dependencies");
    final mirror = currentMirrorSystem().isolate.rootLibrary;

    for (var d in mirror.libraryDependencies) {
      print(d.targetLibrary.simpleName);
      print(d.metadata);
    }
  }

  {
    print("### Annotation on class, field and parameters");
    final mirror = reflectClass(Bar);
    print(mirror.metadata);
    print((mirror.declarations[#it] as VariableMirror).metadata);
    for (var p in (mirror.declarations[#doIt] as MethodMirror).parameters) {
      print("${p.simpleName} -> ${p.metadata}");
    }
  }
}

Output with Dart 1.24.3

## Annotation on dependencies
Symbol("dart.mirrors")
[InstanceMirror on Instance of 'Foo']
Symbol("dart.core")
[]
### Annotation on class, field and parameters
[InstanceMirror on Instance of 'Foo']
[InstanceMirror on Instance of 'Foo']
Symbol("param") -> [InstanceMirror on Instance of 'Foo']

Output with Dart 2.0.0-dev.67.0

### Annotation on dependencies
Symbol("dart.mirrors")
[]
### Annotation on class, field and parameters
[InstanceMirror on Instance of 'Foo']
[InstanceMirror on Instance of 'Foo']
Symbol("param") -> []

[sestegra]

Output with 6dfc4ef revision

### Annotation on dependencies
Symbol("dart.mirrors")
[]
### Annotation on class, field and parameters
[InstanceMirror on Instance of 'Foo']
[InstanceMirror on Instance of 'Foo']
Symbol("param") -> [InstanceMirror on Instance of 'Foo']

So only annotation on dependencies is still missing.

[thosakwe]

Likely related to:

• dart:mirrors fails to find metadata on method parameters with --preview-dart-2 #33207
• ObjectMirror.invoke ignores typeArguments #33594

[sestegra]

I found that dependencies annotations are not implemented.
I've started to investigate on the source code.
At least, the following patch should be applied.

diff --git a/runtime/vm/compiler/frontend/kernel_translation_helper.cc b/runtime/vm/compiler/frontend/kernel_translation_helper.cc
index ac65dec..5fac295 100644
--- a/runtime/vm/compiler/frontend/kernel_translation_helper.cc
+++ b/runtime/vm/compiler/frontend/kernel_translation_helper.cc
@@ -1304,7 +1304,10 @@ void LibraryDependencyHelper::ReadUntilExcluding(Field field) {
     }
       /* Falls through */
     case kAnnotations: {
-      helper_->SkipListOfExpressions();
+      annotation_count_ = helper_->ReadListLength();  // read list length.
+      for (intptr_t i = 0; i < annotation_count_; ++i) {
+        helper_->SkipExpression();  // read ith expression.
+      }
       if (++next_read_ == field) return;
     }
       /* Falls through */
diff --git a/runtime/vm/compiler/frontend/kernel_translation_helper.h b/runtime/vm/compiler/frontend/kernel_translation_helper.h
index 342a8de..ee81079 100644
--- a/runtime/vm/compiler/frontend/kernel_translation_helper.h
+++ b/runtime/vm/compiler/frontend/kernel_translation_helper.h
@@ -729,7 +729,7 @@ class LibraryDependencyHelper {
   };

   explicit LibraryDependencyHelper(KernelReaderHelper* helper)
-      : helper_(helper), next_read_(kFileOffset) {}
+      : annotation_count_(0), helper_(helper), next_read_(kFileOffset) {}

   void ReadUntilIncluding(Field field) {
     ReadUntilExcluding(static_cast<Field>(static_cast<int>(field) + 1));
@@ -740,6 +740,7 @@ class LibraryDependencyHelper {
   uint8_t flags_;
   StringIndex name_index_;
   NameIndex target_library_canonical_name_;
+  intptr_t annotation_count_;

  private:
   KernelReaderHelper* helper_;

[sestegra]

I guess that void KernelLoader::LoadLibraryImportsAndExports(Library* library) method has to be updated as well (from runtime/vm/kernel_loader.cc file).

[sestegra]

I'm close to the solution, but I'm only starting to understand C++ source.
This patch is crashing at "BuildAnnotations".

diff --git a/runtime/vm/kernel_loader.cc b/runtime/vm/kernel_loader.cc
index 114ae9a..920740f 100644
--- a/runtime/vm/kernel_loader.cc
+++ b/runtime/vm/kernel_loader.cc
@@ -869,6 +869,7 @@ void KernelLoader::LoadLibraryImportsAndExports(Library* library) {
   const intptr_t deps_count = builder_.ReadListLength();
   for (intptr_t dep = 0; dep < deps_count; ++dep) {
     LibraryDependencyHelper dependency_helper(&builder_);
+    intptr_t library_dependency_kernel_offset = builder_.ReaderOffset();
     dependency_helper.ReadUntilExcluding(LibraryDependencyHelper::kCombinators);

     // Ignore the dependency if the target library is invalid.
@@ -937,6 +938,14 @@ void KernelLoader::LoadLibraryImportsAndExports(Library* library) {
         }
       }
     }
+
+    if (FLAG_enable_mirrors && (dependency_helper.annotation_count_ > 0)) {
+      AlternativeReadingScope alt(&builder_.reader_, library_dependency_kernel_offset);
+      LibraryDependencyHelper dependency_helper(&builder_);
+      dependency_helper.ReadUntilExcluding(LibraryDependencyHelper::kAnnotations);
+      Object& metadata = Object::ZoneHandle(Z, builder_.BuildAnnotations());
+      target_library.AddLibraryMetadata(metadata, builder_.ReadPosition());
+    }
   }
 }

[sestegra]

@alexmarkov, @rmacnak-google
Could you give me small help ?
I know well Dart, but I'm only a beginner on C++ source code.

[sestegra]

Thanks