CA2021 Do not call Enumerable.Cast<T> or Enumerable.OfType<T> false positives

[buyaa-n]

Analyzer

Diagnostic ID: CA2021: Do not call Enumerable.Cast<T> or Enumerable.OfType<T> with incompatible types

Analyzer source

SDK: Built-in CA analyzers in .NET 8 SDK or later

Describe the bug

Following false positives found in runtime test builds (normally we don't turn on analyzers in test projects, but this analyzer warns by default therefore failing the test builds). So, we have lowered the analyzer severity into info level until these bugs fixed. @fowl2 please let us know if you interested in fixing these, thanks!

1. False positive with dynamic expressions:

  // Type 'int' is incompatible with type 'dynamic' and cast attempts will throw InvalidCastException at runtime
     int[] numbers = new int[] { 1, 2, 3 };
     var v = from dynamic d in numbers select (int)d;

2. False positive with nullability annotations:

  // Type 'int' is incompatible with type 'int?' and cast attempts will throw InvalidCastException at runtime
    Enumerable.Range(1, 5).Cast<int?>();

3. False positive with ValueTuple

  // Type '(int, int)' is incompatible with type '(int min, int max)' and cast attempts will throw InvalidCastException at runtime
    from (int min, int max) pair in new[] { (1, 2), (-10, -3) };

4. For this one don't have a sample repro yet, check the runtime code for more details

// `Type 'System.Collections.Generic.KeyValuePair<string, System.Text.RegularExpressions.Group>' is incompatible with type 'System.Text.RegularExpressions.Group' and cast attempts will throw InvalidCastException at runtime`
     var actualSet = new HashSet<(int start, int end)>(
                match.Groups
                .Cast<Group>()
                .Select(g => (start: g.Index, end: g.Index + g.Length)));

Expected behavior

No warning

Actual behavior

Warns

Additional context

Found in: dotnet/runtime@f3bcd21

CC @fowl2 @stephentoub

[fowl2]

@buyaa-n I've started work on this

[hoyosjs]

There's one other case I think this is throwing a warning where I didn't quite expect it:

        [Fact]
        public async Task CanCastReadonlyStructToInterface()
        {
            await VerifyCS.VerifyAnalyzerAsync(@"
using System.Collections;
using System.Collections.Generic;
using System.Linq;

interface IInterface {}

readonly struct Implementation : IInterface {}

class C
{
    void M()
    {
        IEnumerable<Implementation> e = default;
        e.Cast<IInterface>();
    }
}
");
        }

The problem is

https://github.com/dotnet/roslyn-analyzers/blob/main/src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Runtime/DoNotCallEnumerableCastOrOfTypeWithIncompatibleTypesAnalyzer.cs#L318-L319

It doesn't consider interfaces on structs.

[buyaa-n]

It doesn't consider interfaces on structs.

Right, @hoyosjs is this blocking any repo build or PR?

CC @fowl2 could you fix this?

[hoyosjs]

I submitted the fix PR. Its not blocking. We wanted to enable the rule in a repo that's gonna be merged into another one that has the rule enabled. This flags and breaks the build. We'll update the analyzer when it becomes available.

Cc: @leculver

[buyaa-n]

Thanks @hoyosjs, the fix merged, closing this issue