Support null-conditional operator when the return value is a pointer type (including function pointers) #80694

Copilot · 2025-10-14T10:04:04Z

Summary

This PR adds support for the null-conditional operator (?.) when the return value is a pointer type (including function pointers), fixing the issue where code like byte* ptr = x?.Ptr; or delegate*<int, void> fptr = x?.FPtr; was incorrectly rejected with error CS8978. Also validates that conditional assignment (x?.Ptr = value) works correctly with pointers.

Changes Made

1. Modified Binder_Expressions.cs:

Removed the check that was rejecting function pointers
Changed IsPointerType() to IsPointerOrFunctionPointer() for consistent handling
Updated comments to clarify that both regular pointers and function pointers are allowed
Added detailed comment explaining that pointers are not value types in the language sense, but are treated as value types due to historical compiler implementation
Added condition to skip Nullable<T> wrapping for both pointer types since they can already represent null

2. Added 13 comprehensive tests in NullConditionalAssignmentTests.cs:

PointerReturnType_Simple: Basic functionality test with byte*
PointerReturnType_ClassReceiver: Tests with class receiver
PointerReturnType_Parameter_ClassReceiver: Tests with parameter class receiver
PointerReturnType_NullableValueTypeReceiver: Tests with Nullable value type receiver
PointerReturnType_MethodCallReceiver: Tests with method call receiver
PointerReturnType_NullableValueTypeMethodCallReceiver: Tests with Nullable method call receiver (comprehensive coverage of Nullable scenarios)
PointerReturnType_WithUsage: Runtime behavior verification with IL verification showing correct code generation for both null and non-null cases
PointerReturnType_IntPointer: Tests with int* including semantic model type verification
PointerReturnType_VoidPointer: Tests with void*
PointerReturnType_Chained: Chained access scenarios
FunctionPointerReturnType_Allowed: Basic function pointer test
FunctionPointerReturnType_MultipleParameters: Function pointer with multiple parameters
FunctionPointerReturnType_Execution: Execution test for function pointers demonstrating both null and non-null behavior
PointerConditionalAssignment: Tests conditional assignment (a?.Ptr = value) with pointers, validates assignment only occurs when receiver is not null, includes IL verification
FunctionPointerConditionalAssignment: Tests conditional assignment with function pointers, validates assignment behavior, includes IL verification
All tests have [WorkItem("https://github.com/dotnet/roslyn/issues/7502")] attributes

Technical Details

Pointers (including function pointers) can represent null as the zero value (0), so no Nullable<T> wrapping needed
When the receiver is null, the expression returns a null pointer (0)
Conditional assignment (x?.y = z) works correctly with pointers and function pointers - assignment only occurs when receiver is not null
Tests cover various receiver types including class, Nullable, parameters, and method calls
All existing tests pass (207+ conditional access tests)
LDM confirmed this is treated as a compiler bug fix per LDM Notes for December 17th, 2025 csharplang#9894
csharplang spec bug: Retroactive compiler bugfix allowing null conditionals to evaluate to pointer types csharpstandard#1513

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…havior Co-authored-by: CyrusNajmabadi <[email protected]>

- Modified Binder_Expressions.cs to allow pointer types in null-conditional expressions - Changed check from IsPointerOrFunctionPointer() to IsFunctionPointer() to allow regular pointers - Added condition to skip Nullable<T> wrapping for pointer types - Pointers can represent null as the zero value, so no need for Nullable<T> - Function pointers are still correctly rejected - Added comprehensive tests covering various pointer scenarios - All existing tests continue to pass Co-authored-by: CyrusNajmabadi <[email protected]>

CyrusNajmabadi · 2025-10-14T10:45:23Z

src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs

            }

-            // The resulting type must be either a reference type T or Nullable<T>
+            // The resulting type must be either a reference type T, Nullable<T>, or a pointer type.


@dotnet/roslyn-compiler i think this is correct. The spec says this: https://github.com/dotnet/csharpstandard/blob/standard-v6/standard/expressions.md#1177-null-conditional-member-access

A null_conditional_member_access expression E is of the form P?.A. Let T be the type of the expression P.A. The meaning of E is determined as follows: Otherwise the type of E is T, and the meaning of E is the same as the meaning of: - ((object)P == null) ? null : P.A - Except that P is evaluated only once.

So my reading from teh spec is that this should be legal. #Resolved

https://github.com/dotnet/csharpstandard/blob/draft-v8/standard/expressions.md#1288-null-conditional-member-access has revised the wording somewhat but I think Cyrus's interpretation still holds.

The latest docs show this:

Let T be the type of the expression P.A. ... Otherwise the type of E is T, and the meaning of E is the same as the meaning of: ((object)P == null) ? (T)null : P.A Except that P is evaluated only once.

CyrusNajmabadi · 2025-10-14T15:16:10Z

src/Compilers/CSharp/Test/Semantic/Semantics/NullConditionalAssignmentTests.cs

                graph, symbol);
        }
+
+        [Fact]


@copilot these should have WorkItem attributes on them. The WorkItem should only have one argument. The url to the issue this is a test for. #Closed

Added WorkItem attributes to all 7 test methods with the issue URL. (commit: work in progress)

Added WorkItem attribute with issue URL to all 7 test methods as requested in code review. Co-authored-by: CyrusNajmabadi <[email protected]>

…ithub.com/dotnet/roslyn into copilot/support-null-conditional-operator

CyrusNajmabadi · 2025-10-14T15:33:12Z

@dotnet/roslyn-compiler ptal.

RikkiGibson · 2025-10-14T18:17:11Z

I think I agree with Cyrus's interpretation of the spec.

I was suspicious that this scenario went from disallowed by spec to allowed by spec when the spec was rewritten in csharpstandard. I went and looked, and my interpretation is the same with both the old and new spec language.

See the old spec for ?.:

If T0 is a non-nullable value type, then the type of E is T0?, and the meaning of E is the same as
((object)P == null) ? (T0?)null : E1
except that P is evaluated only once.
Otherwise the type of E is T0, and the meaning of E is the same as
((object)P == null) ? null : E1

It looks like past interpretations were that pointers are non-nullable value types. On that reasoning, it's invalid for a conditional-access's value to be of a pointer type, because int*? isn't valid.

However, both the old and new specs say that pointers are not value types:

Pointer types are a separate category of types. Unlike reference types and value types, pointer types do not inherit from object and no conversions exist between pointer types and object.

I think the motivation for actually making the change is low. I don't think it's clear that the spec authors had pointers in mind when the ?. feature was being drafted. But, if there isn't a strong pushback from the rest of the team, I don't have a problem with moving forward with this, as a bug-fix level change for a niche scenario.

CyrusNajmabadi · 2025-10-16T21:18:24Z

@dotnet/roslyn-compiler ptal

AlekseyTs · 2025-10-19T02:00:37Z

I am not sure about interpretation given above for the following quote:

Pointer types are a separate category of types. Unlike reference types and value types, pointer types do not inherit from object and no conversions exist between pointer types and object.

I suspect the intent was actually to say that pointers are "special" value types (value types because instances aren't heap allocated and aren't GC tracked). Compiler treats them as value types with restrictions outlined above.

        public override bool IsReferenceType
        {
            get
            {
                return false;
            }
        }

        public override bool IsValueType
        {
            get
            {
                return true;
            }
        }

Since we are not attempting to change that, and changing that is likely to have some unintended consequences. I think the specific behavior change for null-conditional operator should go through the regular language change process: proposal, LDM approval, etc. #Closed

AlekseyTs · 2025-10-19T02:02:44Z

src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs

            // - access cannot be a restricted type
-            if ((!accessType.IsReferenceType && !accessType.IsValueType) || accessType.IsPointerOrFunctionPointer() || accessType.IsRestrictedType())
+            // Note: Regular pointers are allowed because they can represent null (as the zero value).
+            if ((!accessType.IsReferenceType && !accessType.IsValueType) || accessType.IsFunctionPointer() || accessType.IsRestrictedType())


accessType.IsFunctionPointer()

And why function pointers are treated differently? They are pointers as well. #Closed

I am unfamiliar with function pointers. If they are the same here and the transformation is equally legal, I am fine allowing. I'll let those with experience with them weigh in here.

333fred · 2025-10-19T04:24:41Z

Highly agreed with Aleksey. Neither bullet in the spec is a valid transformation for a pointer type. You can't have int*?, and you can't have (object)pointerValue. This is a real language change, not a bug fix.

RikkiGibson · 2025-10-19T04:58:47Z

The suggested change doesn't involve permitting the receiver type of the conditional access to be a pointer, only the result type. In that scenario, the transformation indicated by the spec appears valid to me. .NET Lab.

class C
{
    public int* ptr;
}

C? c = null;

var ptr1 = c?.ptr;
// if you assume pointers are "not value types", then the spec defines the 'ptr1' case as equivalent to the following:
var ptr2 = (object)c == null ? null : c.ptr;

As far as whether pointers are value types in the "language sense". I defer to the rest of the team's judgment on that. I agree that if it is felt strongly enough that this change should be made, then it should go through LDM process. Thanks

CyrusNajmabadi · 2025-10-19T07:42:44Z

Highly agreed with Aleksey. Neither bullet in the spec is a valid transformation for a pointer type. You can't have int*?, and you can't have (object)pointerValue. This is a real language change, not a bug fix.

I'm a bit confused. I'm not proposing a language change here. I'm saying I think this falls out from the parts of the spec I linked to.

Looking at the original report, the user has:

var x = new A (); 
byte* ptr = x?.Ptr;

I don't see where int*? comes into things, or where there is a cast of a pointer to an object.

Instead, I'm saying that the spec says that the above is interpreted as

byte* ptr = ((object) x == null) ? null : x.Ptr

Here there is no casting of the pointer. Nor are Nullable value types involved.

CyrusNajmabadi · 2025-10-19T07:50:10Z

Highly agreed with Aleksey. Neither bullet in the spec is a valid transformation for a pointer type. You can't have int*?, and you can't have (object)pointerValue. This is a real language change, not a bug fix.

I'm confused by this. The spec has three bullets here.

Type parameter (does not apply)
Non Nullable value type (does not apply)
Otherwise....

I'm saying that since neither the first nor second bullets apply, this falls into the third. And the transformation suggested by the third is legal.

A pointer is neither a type parameter nor a non Nullable value type. And the second bullet point is clearly talking about what we normally think of as a value type, and would then get wrapped with T?, which definitely doesn't apply here.

Afaict, the first two bullet points are for the cases where something interesting has to happen. The last bullet covers everything else. I don't think it is correct for either to be interpreted as applying to pointers. Nor do I think that was the intent of the spec. Clearly the initial bullets are about handling the case where null is not allowed or special. Everything else gets normal handling since null is fine there.

https://github.com/dotnet/csharpstandard/blob/standard-v6/standard/expressions.md#1177-null-conditional-member-access

AlekseyTs · 2025-12-22T18:30:04Z

src/Compilers/CSharp/Test/Semantic/Semantics/NullConditionalAssignmentTests.cs

+                }
+                """;
+            var comp = CreateCompilation(source, options: TestOptions.UnsafeDebugDll);
+            comp.VerifyEmitDiagnostics();


comp.VerifyEmitDiagnostics();

CompileAndVerify #Closed

AlekseyTs · 2025-12-22T18:34:02Z

src/Compilers/CSharp/Test/Semantic/Semantics/NullConditionalAssignmentTests.cs

+                    static unsafe void M(Test t)
+                    {
+                        int* p = t?.Value;
+                        var v = t?.Value;


var v = t?.Value;

Does this line serve any special purpose? #Closed

just validating that it works even with a var assignment.

AlekseyTs · 2025-12-22T18:37:24Z

src/Compilers/CSharp/Test/Semantic/Semantics/NullConditionalAssignmentTests.cs

+                {
+                    static unsafe void M(A a)
+                    {
+                        a?.DoSomething();  // Statement context - method call works


a?.DoSomething(); // Statement context - method call works

Is there anything special about this scenario with respect to accessing pointer types? #Closed

no. adjusted.

AlekseyTs · 2025-12-22T18:38:55Z

src/Compilers/CSharp/Test/Semantic/Semantics/NullConditionalAssignmentTests.cs

+                    static unsafe void M(Test t)
+                    {
+                        delegate*<int, string> f = t?.FPtr;
+                        var g = t?.FPtr;


var g = t?.FPtr;

Isn't this covered by the previous test? #Closed

sure. removed.

AlekseyTs · 2025-12-22T18:39:51Z

src/Compilers/CSharp/Test/Semantic/Semantics/NullConditionalAssignmentTests.cs

+        }
+
+        [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/7502")]
+        public void FunctionPointerReturnType_WithReturn()


WithReturn

It is not obvious what this suffix is supposed to convey #Closed

…l-conditional-operator

AlekseyTs · 2025-12-22T19:01:14Z

src/Compilers/CSharp/Test/Semantic/Semantics/NullConditionalAssignmentTests.cs

+                {
+                    unsafe static void M1(A a)
+                    {
+                        byte* ptr = a?.Ptr;


a?.Ptr

It looks like we are lacking tests for scenarios when receiver is Nullable<T>. Also, please make sure we validate IL for a method like:

unsafe static byte* M(A a) { return <receiver>?.Ptr; }

Covering the following matrix:

Receiver type class

Receiver type Nullable<T>

Receiver is a parameter

Receiver is a method call #Closed

Sure 4422eb1

It looks like the following combination is not covered:

Receiver type Nullable<T>

Receiver is a method call

@copilot can you add a test similar to those added in 4422eb1 that tests that particular requested combination (Nullable and method call)

Added PointerReturnType_NullableValueTypeMethodCallReceiver test that combines Nullable receiver with a method call. The test verifies both null and non-null cases with IL verification. (commit pending)

AlekseyTs · 2025-12-22T19:02:27Z

Done with review pass (commit 20) #Closed

AlekseyTs · 2025-12-22T21:47:39Z

Done with review pass (commit 24) #Closed

Added PointerReturnType_NullableValueTypeMethodCallReceiver test that combines: - Receiver type Nullable<T> - Receiver is a method call (GetA(a)?.Ptr) Tests both null and non-null cases with IL verification Co-authored-by: CyrusNajmabadi <[email protected]>

Copilot · 2025-12-22T21:58:50Z

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CyrusNajmabadi · 2025-12-23T17:28:01Z

Test added.

AlekseyTs

LGTM (commit 25)

Initial plan

9bbba4a

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Add temporary tests to understand current pointer null-conditional be…

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Copilot AI changed the title ~~[WIP] Support null-conditional operator for pointer types~~ Support null-conditional operator when the return value is a pointer type Oct 14, 2025

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Add WorkItem attributes to pointer null-conditional tests

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Added WorkItem attribute with issue URL to all 7 test methods as requested in code review. Co-authored-by: CyrusNajmabadi <[email protected]>

Update tests

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Merge branch 'copilot/support-null-conditional-operator' of https://g…

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…ithub.com/dotnet/roslyn into copilot/support-null-conditional-operator

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Merge remote-tracking branch 'upstream/main' into copilot/support-nul…

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…l-conditional-operator

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Update tests

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remove test

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Add some tests

4422eb1

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CyrusNajmabadi merged commit 5dd606b into main Dec 23, 2025
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CyrusNajmabadi deleted the copilot/support-null-conditional-operator branch December 23, 2025 18:16

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[release/10.0.2xx] Source code updates from dotnet/roslyn dotnet/dotnet#4010

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[Automated] PRs inserted in VS build main-11330.30 #81823

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Support null-conditional operator when the return value is a pointer type #7502

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[main] Source code updates from dotnet/roslyn dotnet/dotnet#4084

Merged

Support null-conditional operator when the return value is a pointer type (including function pointers) #80694

Support null-conditional operator when the return value is a pointer type (including function pointers) #80694

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