Analyzer support for Dart 1.50 non strong mode generic methods.

[leafpetersen]

We have an informal specification for Dart 1.50 generic methods here:

https://docs.google.com/document/d/1nccOSkdSyB9ls7TD8gUqIu6Wl2J_9bTSOoMCEIoAiQI/edit#heading=h.dnanv15dn1me

The analyzer should remove the partial support for error checking on generic methods (or make them into hints as warranted).

The only static errors for Dart 1.5 non strong mode generic methods are syntax errors, and errors for using a generic method parameter for an is check as in x is T, or as a type literal.

[kulshekhar]

Can the linked document be publicly shared?

[eernstg]

Here's a public version of the informal specification of generic method syntax that Leaf mentioned. Note that we do not commit to the contents of this file, things may still change!

Update Nov 2nd: We are now implementing this feature, and the informal specification is not expected to change any more.

[bwilkerson]

I believe that https://codereview.chromium.org/2487583002/ correctly converts errors to hints in the non-strong-mode case.

As far as I know the only remaining step is to remove the flag, so please let me know when doing so is appropriate.

[leafpetersen]

At some point there should be a non-strong mode error when a generic method parameter is used directly in an is check (e.g. x is T). Note though that x is List<T> is not an error.

This error is just transitional, to ensure that users do not rely on instance check behavior that will differ between strong mode and non-strong mode.

[bwilkerson]

Error, warning, or hint?

[leafpetersen]

It is an error.

[leafpetersen]

Also note, the error is only in an 'is' check, not in a cast expression ('x as T').