Create vm service models about webdev

[jakemac53]

Actually, it looks like https://github.com/dart-lang/vm_service_drivers already has a parser for the markdown file, and we could likely just add serialization logic to that generator and use that package instead of maintaining our own yaml file.

[jakemac53]

Example yaml file for all the models up to and including the Event type:

classes:
  BoundField:
    fields:
      decl:
        type: '@Field'
      value:
        type: '@Instance|Sentinel'
  BoundVariable:
    fields:
      name:
        type: string
      value:
        type: '@Instance|@TypeArguments|Sentinel'
      declarationTokenPos:
        type: int
      scopeStartTokenPos:
        type: int
      scopeEndTokenPos:
        type: int
  Breakpoint:
    extends: Object
    fields:
      breakpointNumber:
        type: int
      resolved:
        type: bool
      isSyntheticAsyncContinuation:
        type: bool
        optional: true
      location:
        type: SourceLocation|UnresolvedSourceLocation
  '@Class':
    extends: '@Object'
    fields:
      name:
        type: string
  Class:
    extends: Object
    fields:
      name:
        type: string
      error:
        type: '@Error'
        optional: true
      abstract:
        type: bool
      const:
        type: bool
      library:
        type: '@Library'
      location:
        type: SourceLocation
        optional: true
      super:
        type: '@Class'
        optional: true
      superType:
        type: '@Instance'
        optional: true
      interfaces:
        type: '@Instance[]'
      mixin:
        type: '@Instance'
        optional: true
      fields:
        type: '@Field[]'
      functions:
        type: '@Function[]'
      subclasses:
        type: '@Class[]'
  ClassList:
    extends: Response
    fields:
      classes: '@Class[]'
  '@Code':
    extends: '@Object'
    fields:
      name:
        type: string
      kind:
        type: CodeKind
  Code:
    extends: '@Object'
    fields:
      name:
        type: string
      kind:
        type: CodeKind
  '@Context':
    extends: '@Object'
    fields:
      length:
        type: int
  Context:
    extends: Object
    fields:
      length:
        type: int
      parent:
        type: Context
        optional: true
      variables:
        type: 'ContextElement[]'
  ContextElement:
    fields:
      value:
        type: '@Instance|Sentinel'
  '@Error':
    extends: '@Object'
    fields:
      kind:
        type: ErrorKind
      message:
        type: string
  Error:
    extends: Object
    fields:
      kind:
        type: ErrorKind
      message:
        type: string
      exception:
        type: '@Instance'
        optional: true
      stacktrace:
        type: '@Instance'
        optional: true
  Event:
    extends: Response
    fields:
      kind:
        type: EventKind
      isolate:
        type: '@Isolate'
        optional: true
      vm:
        type: '@VM'
        optional: true
      timestamp:
        type: int
      breakpoint:
        type: Breakpoint
        optional: true
      pauseBreakpoints:
        type: Breakpoint[]
        optional: true
      topFrame:
        type: Frame
        optional: true
      exception:
        type: '@Instance'
        optional: true
      bytes:
        type: string
        optional: true
      inspectee:
        type: '@Instance'
        optional: true
      extensionRPC:
        type: string
        optional: true
      extensionKind:
        type: string
        optional: true
      extensionData:
        type: ExtensionData
        optional: true
      timelineEvents:
        type: TimelineEvent[]
        optional: true
      atAsyncSuspension:
        type: bool
        optional: true
      status:
        type: String
        optional: true

enums:
  CodeKind:
    - Dart
    - Native
    - Stub
    - Tag
    - Collected
  ErrorKind:
    - UnhandledException
    - LanguageError
    - InternalError
    - TerminationError

[natebosch]

When we say "extends" here does that translate to an extends in the generated Dart code? That precludes generating correct equals implementations if subclasses add fields...

[jakemac53]

When we say "extends" here does that translate to an extends in the generated Dart code?

Yes

That precludes generating correct equals implementations if subclasses add fields...

how so? also i don't think this is a requirement for us in any case (I wasn't planning on implementing equals or hashCode)

[jakemac53]

fwiw, it seems like you can do:

bool operator==(other) => other is ThisType && other.someField == someField && super == other;

a bit bizarre, but it appears to work

[natebosch]

how so?

In Dart (as in many other OO languages) you cannot use extends with an instantiable super class and implement operator== on both that follows the contract and the Liskov Substitution Principle.

The docs say that the operator must be symmetric.

If the implementation of SuperType.operator== checks other is SuperType, and the SubType.operator== checks other is SubType, then this property is not held.

var a = SuperType();
var b = SubType();
a == b; // true, b is SuperType holds
b == a; // false, a is SubType does not hold

If you try to get around this problem by using other.runtimeType == SuperType then you can fix the symmetry, but fail Liskov Substitution because an instance of SubType is no longer indistinguishable from a SuperType when used as such.

I think you can get around the problem if you ignore the extra fields in SubType when it comes to equality, but that ends up being a pretty lame implementation.
You can also get around the problem if only the leaf classes are instantiable and the super types are abstract.

[jakemac53]

Ah ya good point, we can just ignore equals for now.