Type inference fails for lambda expression returning collection expression

[cston]

Steps to Reproduce:

Compile:

using System;
using System.Collections.Generic;

class Program
{
    static void TupleResult<T>(Func<(T, T)> x)
    {
        Console.WriteLine(typeof(T).Name);
    }

    static void CollectionResult<T>(Func<T[]> x)
    {
        Console.WriteLine(typeof(T).Name);
    }

    static void Main()
    {
        TupleResult(() => (1, 2));
        CollectionResult(() => new[] { 1, 2 });
        CollectionResult(() => [1, 2]);
    }
}

Expected Behavior:
No errors, program reports "Int32 Int32 Int32".

Actual Behavior:
Error reported for collection expression case.

(20,9): error CS0411: The type arguments for method 'Program.CollectionResult<T>(Func<T[]>)'
    cannot be inferred from the usage. Try specifying the type arguments explicitly.

Relates to test plan #66418

[cston]

The current behavior is by design since output type inference from a lambda expression requires the return value has a type. Since collection expressions do not have a natural type, type inference in the example fails as expected.

See 11.6.3.7 Output type inference:

• If E is an anonymous function with inferred return type U and T is a delegate type or expression tree type with return type Tₓ, then a lower-bound inference is made from U to Tₓ.

See also collection expressions which builds on the output type inference rules.

[cston]

Added test for current (expected) behavior in #71017.