analyzer: InheritanceManager3.getInheritedConcreteMap2 throws, given an extension type

[srawlins]

Ran across this while working extension type support into dartdoc. I think it is valid to pass an extension type-derived InterfaceElement to InheritanceManager3.getInheritedConcreteMap2, but that method then throws this:

Bad state: No element

dart:core-patch/array.dart 56:5                                           _Array.last
package:analyzer/src/dart/element/inheritance_manager3.dart 178:39        InheritanceManager3.getInheritedConcreteMap2
pkg/analyzer/test/src/dart/element/inheritance_manager3_test.dart 448:27  InheritanceManager3Test_ExtensionType.test_getInheritedConcreteMap_x
===== asynchronous gap ===========================
package:test_reflective_loader/test_reflective_loader.dart 281:21         _runTest.<fn>
===== asynchronous gap ===========================
package:test_api/src/backend/declarer.dart 215:9                          Declarer.test.<fn>.<fn>
===== asynchronous gap ===========================
package:test_api/src/backend/declarer.dart 213:7                          Declarer.test.<fn>
===== asynchronous gap ===========================
package:test_api/src/backend/invoker.dart 258:9                           Invoker._waitForOutstandingCallbacks.<fn>

because InheritanceManager3._getInterfaceExtensionType returns Interface._(..., superImplemented: const []).

CC @scheglov

[scheglov]

The documentation says about superclasses and mixins.

  /// Return signatures of all concrete members that the given [element] inherits
  /// from the superclasses and mixins.
  Map<Name, ExecutableElement> getInheritedConcreteMap2(
      InterfaceElement element) {
    var interface = getInterface(element);
    return interface.superImplemented.last;
  }

And extension types don't have them.

What is the use case for invoking it for extension types?

[srawlins]

Given this code:

extension type ET(int it) implements num {}

I can call .abs() on an expression of type ET. But ET does not declare abs. If it doesn't "inherit" it either, what word do we use?

Even if I should not be calling getInheritedConcreteMap2 with an extension type, it should not crash.

[scheglov]

Inherited methods are not necessary concrete.
So, getInheritedConcreteMap2() is wrong API for this.
I think we should use getInheritedMap2() instead.

https://dart-review.googlesource.com/c/sdk/+/329782 adds a check to prevent the crash, and expands the test to print inheritedMap.

[srawlins]

Excellent thanks for the tip!