Reinfer GetEnumerator type based on input type. #35151
Description
using System.Collections;
class C
{
void M1(IEnumerator e)
{
var enumerable1 = Create(e);
foreach (var i in enumerable1)
{
}
e = null; // 1
var enumerable2 = Create(e);
foreach (var i in enumerable2) // 2
{
}
}
void M2(IEnumerator? e)
{
var enumerable1 = Create(e);
foreach (var i in enumerable1) // 3
{
}
if (e == null) return;
var enumerable2 = Create(e);
foreach (var i in enumerable2)
{
}
}
static Enumerable<T> Create<T>(T t) where T : IEnumerator? => throw null!;
}
class Enumerable<T> where T : IEnumerator?
{
public T GetEnumerator() => throw null!;
}This test should have warnings on the foreachs indicated. In addition to the GetEnumerator reinference, this also exposes that when we do the visit of the foreach expression, we need to explicitly remove implicit conversions from the expression and call ApplyConversion ourselves.