analyzer should warn about final super parameters

[goderbauer]

class Base {
  Base(this.value);
  final int value;
}

class Extended extends Base {
  Extended(final super.value); // note the incorrect final here
}

The analyzer doesn't think anything is wrong with this code, but when I execute it, I get the following error:

Error: Can't have modifier 'final' here.
Try removing 'final'.
  Extended(final super.value);
           ^^^^^

The analyzer should tell me about this problem while I write the code so I can correct it before running my program.

(This was discovered while debugging #48698)

[goderbauer]

/cc @pq

[bwilkerson]

@scheglov

[scheglov]

Why? Is it specified somewhere?
I see that const, late and var are disallowed.

And the super-formal parameters specification also mentions var, super and late.

But in the language specification I see finalConstVarOrType in fieldFormalParameter, so I guess final is allowed.

And this code works fine in VM.

class A {
  final int value;
  A(final this.value);
}

void f(final int value) {}

main() {}

So, I don't see why it should not work for super.name.
@lrhn

[eernstg]

A super parameter is already final, so final should be benign, but redundant. I don't see any rules against it.

[pq]

A super parameter is already final, so final should be benign, but redundant

We could definitely consider linting or hinting for this. My preference would be to make it a hint I guess but maybe I'm missing a reason someone might value this redundancy?

[goderbauer]

If final is allowed there, why does it give a runtime error? Should that error be removed then as well?

[bwilkerson]

Yes, it's a bug that you got a runtime error.

It's effectively dead code, so a hint seems reasonable to me.

[eernstg]

why does it give a runtime error?

Wouldn't that be a compile-time error from the vm, rather than an actual run time error? If this is true then it should be reported as an issue on the common front end.

[asashour]

I understood there is a new issue to be created for the CFE, while this issue is for the analyzer to have a hint.

I am also under the impression that this should also be applied to FieldFormalParameter, since it has the same behavior.

Please look into https://dart-review.googlesource.com/c/sdk/+/239640

[eernstg]

Perhaps the error message from the CFE was emitted by some earlier version? I don't see it with the current CFE, not for a formal of the form final super.x and also not for final this.x.

[asashour]

Or possibly triggered in the last few days in the SDK.

It is reproducible with:

Dart SDK version: 2.17.0-251.0.dev (dev) (Tue Mar 29 00:56:13 2022 -0700) on "windows_x64" (from Flutter master)

[eernstg]

Right, I do get the error, with a bleeding edge dart from ac19f52. So it must be a quite recent change.