`UnsafeAccessor` throws `MissingFieldException` on generic field (`T`)

[AoshiW]

Description

UnsafeAccessor throws MissingFieldException on generic field (T) in generic type, where genetic T is:

• class (e.g. string)
• struct that has class as a generic parameter (e.g. ArraySegment<string>)

Reproduction Steps

[UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_items")]
static extern ref string[] GetItems(List<string> list);

GetItems(new());

Expected behavior

getting field

Actual behavior

throws exception

System.MissingFieldException: Field not found: 'System.Collections.Generic.List`1._items'.

Regression?

No response

Known Workarounds

No response

Configuration

.NET SDK: 8.0.100-rc.1.23455.8

Other information

No response

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Issue Details

---

Description

UnsafeAccessor throws MissingFieldException on generic field (T) in generic type, where genetic T is:

• class (e.g. string)
• struct that has class as a generic parameter (e.g. ArraySegment<string>)

Reproduction Steps

[UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_items")]
static extern ref string[] GetItems(List<string> list);

GetItems(new());

Expected behavior

getting field

Actual behavior

throws exception

System.MissingFieldException: Field not found: 'System.Collections.Generic.List`1._items'.

Regression?

No response

Known Workarounds

No response

Configuration

.NET SDK: 8.0.100-rc.1.23455.8

Other information

No response

Author:	AoshiW
Assignees:	-
Labels:	area-System.Runtime.CompilerServices, untriaged, needs-area-label
Milestone:	-

[jkotas]

cc @AaronRobinsonMSFT

[AaronRobinsonMSFT]

Boo. For my original implementation of the signature match this worked. When I switched to the more robust, but stricter, built-in element compare this support was lost. Le sigh. There is little chance this sort of fix meets the servicing bar. I will take a little bit to try and make it work, but this is likely a .NET 9 fix.

[AaronRobinsonMSFT]

Yep, this is a future fix. If the T is anywhere in the field or method signature this is going to fail.

Let me add some tests for this.

[AaronRobinsonMSFT]

With how this is currently implemented there is some overlap with #89439. The core issue being how we parse and compare signatures.

[AaronRobinsonMSFT]

I've added disabled tests in #92657 and fixed some issues with NAOT.