Analyzer fails to report an error when key in a constant map overrides operator ==

[spkersten]

In the following code:

void main() {
  final foo1 = Bar({const Foo(): ""});  // 1
  final foo2 = const Bar({Foo(): ""});  // 2
}

class Foo {
  const Foo();
  
  bool operator==(dynamic other) => false;
  
  int get hashCode => 1;
}

class Bar {
  const Bar(Map<Foo, String> x);
}

I get a warning for the foo1:

info: Prefer const with constant constructors. (prefer_const_constructors ...

But, with const at foo2, there is an error:

Error compiling to JavaScript:
main.dart:4:22:
Error: Constant evaluation error:
final foo2 = const Bar({Foo(): ""});
^
main.dart:4:27:
Info: The key 'Foo {}' does not have a primitive operator '=='.

• 'Foo' is from 'main.dart'.
  final foo2 = const Bar({Foo(): ""});
  ^
  Error: Compilation failed.

Dart 2.7.0

[bwilkerson]

It appears that the analyzer has failed to provide a required error at foo2. The specification says

It is a compile-time error if the operator ‘==’ of a key in a constant map literal is not primitive (10.1.3).

The analyzer should have produced this error, but didn't.

But the code that produces the prefer_const_constructors lint correctly suppresses that lint if the constructor invocation is implicitly const, which it is in the case of the Foo in foo2.

[spkersten]

A very similar issue:

class Foo {
  const Foo(List<int> numbers)
      : assert(numbers.length > 0),
        assert(numbers.isNotEmpty);
}

The first assert results in a warning say:

info: Use isNotEmpty instead of length (prefer_is_empty at [...] ...)

But following that suggestion (the second assert) is an error:

error: Invalid constant value. (invalid_constant at [...] ...)

[srawlins]

@spkersten That issue is different enough to warrant a new issue, if you'd like to open it.

For the record, neither of those assertions are legal. dart will report each. The analyzer is failing to report the first one.

[spkersten]

@srawlins Created dart-lang/sdk#42354

[bwilkerson]

@mraleph This is actually a bug in analyzer, not in the linter. Could you please move it back to the sdk repo?

[bwilkerson]

Thanks!

@scheglov Looks like analyzer is failing to report an error.

[mraleph]

@bwilkerson I took a liberty to rename the issue to reflect the actual bug - previous title confused me (that's why I moved it to linter).

[scheglov]

https://dart-review.googlesource.com/c/sdk/+/151623