dart fix for avoid_redundant_argument_values makes semantic changes when involving kIsWeb

[Hixie]

dart fix for avoid_redundant_argument_values makes semantic changes when involving kIsWeb.

STEPS TO REPRODUCE

• dart create dart_fix_test
• Replace the dart_fix_test/bin/dart_fix_test.dart file as follows:

void test({ bool foo = true }) { }

const bool kIsWeb = identical(0, 0.0);

void main(List<String> arguments) {
  test(foo: kIsWeb);
}

• Replace the analysis_options.yaml file as follows:

linter:
  rules:
    - avoid_redundant_argument_values

• Run dart fix --apply

EXPECTED RESULTS

The analyzer and dart fix should magically know that identical(0, 0.0) is not a constant value despite it being a constant according to the language, and thus make no change to the code above.

ACTUAL RESULTS

The argument is removed, because kIsWeb is assumed to be true (which is weird in itself, but that's another story) and so the argument is removed. This is, of course, a significant semantic change.

[bwilkerson]

@scheglov @srawlins

This sounds like a possible issue with the constant evaluation engine. Should we consider identical(0, 0.0) to evaluate to a valid bool of unknown value? At one point I think we decided to optimize analyzer for the web case, but I'm not convinced that's still a valid approach (even assuming it was at the time).

[scheglov]

https://dart-review.googlesource.com/c/sdk/+/216923
Lets see what it will do to Flutter bots.

[scheglov]

The original CL where kIsWeb workaround was added is https://dart-review.googlesource.com/c/sdk/+/135781.

[scheglov]

It looks fixed now with the CL landed.

dart_fix_test$ /Users/scheglov/Source/Dart/sdk.git/sdk/xcodebuild/ReleaseX64/dart-sdk/bin/dart fix --apply
Computing fixes in dart_fix_test... 3.6s
Nothing to fix!