Lambdas in best type contribute oblivious type arguments

[jcouv]

        [Fact]
        [WorkItem(33664, "https://github.com/dotnet/roslyn/issues/33664")]
        public void ConditionalOperator_WithLambdaConversions()
        {
            var source = @"
using System;
class C
{
    Func<bool, T> D1<T>(T t) => k => t;

    void M1(bool b, string? s)
    {
        _ = (b ? D1(s) : k => s) /*T:System.Func<bool, string?>!*/;
        _ = (b ? k => s : D1(s)) /*T:System.Func<bool, string?>!*/;
        _ = (true ? D1(s) : k => s) /*T:System.Func<bool, string?>!*/;
        _ = (true ? k => s : D1(s)) /*T:System.Func<bool, string>!*/; // unexpected type
        _ = (false ? D1(s) : k => s) /*T:System.Func<bool, string>!*/; // unexpected type
        _ = (false ? k => s : D1(s)) /*T:System.Func<bool, string?>!*/;

        _ = (b ? D1(s!) : k => s) /*T:System.Func<bool, string>!*/; // 1, unexpected type
        _ = (b ? k => s : D1(s!)) /*T:System.Func<bool, string>!*/; // 2, unexpected type
        _ = (true ? D1(s!) : k => s) /*T:System.Func<bool, string>!*/; // unexpected type
        _ = (true ? k => s : D1(s!)) /*T:System.Func<bool, string>!*/; // 3, unexpected type
        _ = (false ? D1(s!) : k => s) /*T:System.Func<bool, string>!*/; // 4, unexpected type
        _ = (false ? k => s : D1(s!)) /*T:System.Func<bool, string>!*/; // unexpected type

        _ = (b ? D1(true ? throw null! : s) : k => s) /*T:System.Func<bool, string>!*/; // 5, unexpected type
        _ = (b ? k => s : D1(true ? throw null! : s)) /*T:System.Func<bool, string>!*/; // 6, unexpected type
        _ = (true ? D1(true ? throw null! : s) : k => s) /*T:System.Func<bool, string>!*/; // unexpected type
        _ = (true ? k => s : D1(true ? throw null! : s)) /*T:System.Func<bool, string>!*/; // 7, unexpected type
        _ = (false ? D1(true ? throw null! : s) : k => s) /*T:System.Func<bool, string>!*/; // 8, unexpected type
        _ = (false ? k => s : D1(true ? throw null! : s)) /*T:System.Func<bool, string>!*/; // unexpected type
    }

    delegate T MyDelegate<T>(bool b);
    ref MyDelegate<T> D2<T>(T t) => throw null!;

    void M(bool b, string? s)
    {
        _ = (b ? ref D2(s) : ref D2(s!)) /*T:C.MyDelegate<string>!*/; // 9
        _ = (b ? ref D2(s!) : ref D2(s)) /*T:C.MyDelegate<string>!*/; // 10
        _ = (true ? ref D2(s) : ref D2(s!)) /*T:C.MyDelegate<string>!*/; // 11
        _ = (true ? ref D2(s!) : ref D2(s)) /*T:C.MyDelegate<string!>!*/;
        _ = (false ? ref D2(s) : ref D2(s!)) /*T:C.MyDelegate<string!>!*/;
        _ = (false ? ref D2(s!) : ref D2(s)) /*T:C.MyDelegate<string>!*/; // 12
    }
}";

            // See TODO2
            // Best type inference involving lambda conversion should agree with method type inference
            // Missing diagnostics

            var comp = CreateCompilation(source, options: WithNonNullTypesTrue());
            comp.VerifyTypes();
            comp.VerifyDiagnostics(
                // (36,14): warning CS8619: Nullability of reference types in value of type 'C.MyDelegate<string?>' doesn't match target type 'C.MyDelegate<string>'.
                //         _ = (b ? ref D2(s) : ref D2(s!)) /*T:C.MyDelegate<string>!*/; // 9
                Diagnostic(ErrorCode.WRN_NullabilityMismatchInAssignment, "b ? ref D2(s) : ref D2(s!)").WithArguments("C.MyDelegate<string?>", "C.MyDelegate<string>").WithLocation(36, 14),
                // (37,14): warning CS8619: Nullability of reference types in value of type 'C.MyDelegate<string>' doesn't match target type 'C.MyDelegate<string?>'.
                //         _ = (b ? ref D2(s!) : ref D2(s)) /*T:C.MyDelegate<string>!*/; // 10
                Diagnostic(ErrorCode.WRN_NullabilityMismatchInAssignment, "b ? ref D2(s!) : ref D2(s)").WithArguments("C.MyDelegate<string>", "C.MyDelegate<string?>").WithLocation(37, 14),
                // (38,14): warning CS8619: Nullability of reference types in value of type 'C.MyDelegate<string?>' doesn't match target type 'C.MyDelegate<string>'.
                //         _ = (true ? ref D2(s) : ref D2(s!)) /*T:C.MyDelegate<string>!*/; // 11
                Diagnostic(ErrorCode.WRN_NullabilityMismatchInAssignment, "true ? ref D2(s) : ref D2(s!)").WithArguments("C.MyDelegate<string?>", "C.MyDelegate<string>").WithLocation(38, 14),
                // (41,14): warning CS8619: Nullability of reference types in value of type 'C.MyDelegate<string>' doesn't match target type 'C.MyDelegate<string?>'.
                //         _ = (false ? ref D2(s!) : ref D2(s)) /*T:C.MyDelegate<string>!*/; // unexpected type
                Diagnostic(ErrorCode.WRN_NullabilityMismatchInAssignment, "false ? ref D2(s!) : ref D2(s)").WithArguments("C.MyDelegate<string>", "C.MyDelegate<string?>").WithLocation(41, 14)
                );
        }

        [Fact]
        public void ReturnTypeInference_DelegateTypes()
        {
            var source = @"
class C
{
    System.Func<bool, T> D1<T>(T t) => k => t;
    void M1(bool b, string? s, string s2)
    {
        M2(k => s, D1(s)) /*T:System.Func<bool, string?>!*/;
        M2(D1(s), k => s) /*T:System.Func<bool, string?>!*/;

         M2(k => s2, D1(s2)) /*T:System.Func<bool, string!>!*/;
        M2(D1(s2), k => s2) /*T:System.Func<bool, string!>!*/;

         _ = (new[] { k => s, D1(s) }) /*T:System.Func<bool, string?>![]!*/;
        _ = (new[] { D1(s), k => s }) /*T:System.Func<bool, string?>![]!*/;

         _ = (new[] { k => s2, D1(s2) }) /*T:System.Func<bool, string>![]!*/; // wrong
        _ = (new[] { D1(s2), k => s2 }) /*T:System.Func<bool, string>![]!*/; // wrong
    }
    T M2<T>(T x, T y) => throw null!;
}";
            // See TODO2
            // Best type inference involving lambda conversion should agree with method type inference
            var comp = CreateCompilation(source, options: WithNonNullTypesTrue());
            comp.VerifyTypes();
            comp.VerifyDiagnostics();
        }