Unexpected analyze argument_type_not_assignable error

[cyliale]

Hello i have the some analyze errors on use of fnString() and fnInt() when i use this sample test code. Comments in code.

Type seems not promoted in lambda function arguments.

Source code is

bool fnString(final String s) => s == 'text';
bool fnInt(final int i) => i == 1;
void main() {
  test('DART bug : analyze error in expect lambda function', () {
    Object? o = 'text';
    if (o is! String) {
      fail('o should be a String');
    }
    // Ok: unrelated_type_equality_checks lint error for "o == 1" as expected
    expect(o == 1, false);
    // Ok: o is seen as a String
    expect(o == 'text', true);
    // Ok: o is seen as a String
    expect(() => o == 'text', true);
    // Bug: argument_type_not_assignable analyze error
    // o is seen as an Object? instead of a String !!!
    expect(() => fnString(o), true);

    o = 1;
    if (o is! int) {
      fail('o should be an int');
    }
    // Ok: unrelated_type_equality_checks lint error for "o == 'text'" as expected
    expect(o == 'text', false);
    // Ok: o is seen as a int
    expect(o == 1, true);
    // Ok: o is seen as a int
    expect(() => o == 1, true);
    // Bug: argument_type_not_assignable analyze error
    // o is seen as an Object? instead of an int !!!
    expect(() => fnInt(o), true);
  });
}

Dart SDK version: 2.16.1 (stable) (Unknown timestamp) on "linux_x64"

[cyliale]

If i write "final s = o;" just before then "expect(() => fnString(s), true);" has no analyze error.
If i write "final i = o;" just before then "expect(() => fnInt(i), true);" has no analyze error.

But it would be nice to not be obliged to write these additional lines.

[cyliale]

If you need my yaml config.

environment:
  sdk: '>=2.15.0 <3.0.0'

dependencies:
  collection: ^1.15.0
  pub_semver: ^2.0.0
  yaml: ^3.1.0

dev_dependencies:
  lint: ^1.8.1
  matcher: '>=0.12.3 <0.14.0'
  test: ^1.16.0

and my analysis options.

include: all_lint_rules.yaml
analyzer:
  exclude:
  #- '**.freezed.dart'

  strong-mode:
    implicit-casts: false
    implicit-dynamic: false

  errors:
    included_file_warning: ignore
    missing_required_param: error
    missing_return: error
    parameter_assignments: warning
    todo: ignore

linter:
  rules:
    always_specify_types: false
    always_use_package_imports: false
    avoid_annotating_with_dynamic: false
    avoid_final_parameters: false
    prefer_double_quotes: false
    require_trailing_commas: false
    sort_constructors_first: false
    unnecessary_final: false

[cyliale]

Beware, if you separate tests into two separate tests and make the variable "o" "final", the analyze bug disappears.

[bwilkerson]

@stereotype441

[stereotype441]

The first issue (o is seen as an Object? instead of a String in expect(() => fnString(o), true);) is expected behavior. Flow analysis only operates on local information; it doesn't make any assumptions about the behaviors of functions other than the one being analyzed. In particular, it doesn't make any assumptions about when the expect function executes the closure that's passed to it. As far as it knows, expect might save the closure somewhere, and it might get executed at a later time, after o = 1 has been executed. So it can't safely promote the type of o to String inside the closure () => fnString(o).

The second issue (o is seen as an Object? instead of an int in expect(() => fnInt(o), true);) is more unfortunate, and it's something I'm looking into fixing. In this case, flow analysis isn't smart enough to see that at the time of expect(() => fnInt(o), true);, all of the assignments to o are already in the past, and therefore, in effect, o is final now (and therefore safe to promote). This issue is tracked in dart-lang/language#1536.

[cyliale]

Thanks a lot for your explanations and your work.

[srawlins]

I'll close this in favor of dart-lang/language#1536.