Using `VariableElement.computeConstantValue`, can we read fields from superclasses?

[dark...@gmail.com]

Hello!

I was trying to use VariableElement.computeConstantValue to obtain some information about a constant I have full control over.

I was successfully able to read direct field of a given variable. But when trying to read fields coming from the superclass, I seem to always get `null`.

Is it supposed to be possible?

Thanks!

[dark...@gmail.com]

For example, consider:

class Foo extends Bar {

const Foo(this.a, super.b);

final int a;

}

class Bar {

const Bar(this.b);

final int b;

}

const value = Foo(1, 2);

When trying to inspect `value`, calling `DartObject.toString()` on it gives:

Foo ((super) = Bar (b = int (2)); a = int (1))

This suggests that both fields were parsed.

But `getField('a')` returns `1`, yet `getField('b')` returns `null`

[dark...@gmail.com]

Ignore me, I found the solution by adding some prints in the SDK's source.

It seems that we have to do:

`fooObject.getField('(super)')?.getField('b');`

However, I couldn't find this documented anywhere. I thin it'd be variable information to add on `getField`'s dartdoc

[Brian Wilkerson]

It's a bit unfortunate. I believe the reason is because of the possibility of a field in a subclass shadowing a field in a superclass and the occasional need (maybe only in tests) to check that the superclass field has the right value.

It does seem like there could be a better API that would make the common case (where there is no shadowing) easier.

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[dark...@gmail.com]

I ended-up adding an extension method that does a simple recursion:

extension DartObjectSuperField on DartObject {

DartObject? getFieldInThisOrSuper(String name) {

final field = getField(name);

if (field != null) return field;

final superField = getField('(super)');

if (superField == null) return null;

return superField.getFieldInThisOrSuper(name);

}

}

I'm mainly worried about discoverability. That `(super)` syntax isn't well documented.

To find it, I ended up putting a print in DartObjectImpl, to print GenericState._fieldMap.keys

[Brian Wilkerson]

I created https://github.com/dart-lang/sdk/issues/54895 so that we could discuss various possible improvements without loosing the thread.

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