Fix superfluous managed address errors for pointer to non-existent type #80760

Copilot · 2025-10-16T14:14:02Z

Fix superfluous managed address errors for pointer to non-existent type

Summary

Fixed issue #38378 where declaring a pointer to a non-existent type would report both CS0246 (type not found) and CS8500/CS0208 (managed address warning/error). Now only CS0246 is reported.

Changes Made

Binder_Expressions.cs: Added error type check in CheckManagedAddr() to skip the warning only for truly missing types (LookupResultKind.Empty or NotATypeOrNamespace), but still report for other error scenarios like inaccessible types
Binder_Symbols.cs: Removed redundant check (now handled in CheckManagedAddr)
ConstraintsHelper.cs: Removed redundant check (now handled in CheckManagedAddr)
Added 4 comprehensive test cases in UnsafeTests.cs using raw string literals with C# pointer style (Type* instead of Type *)
Updated 2 existing tests (PointerTypeInDeconstruction, TypeNamedFile_03_CSharp11) to reflect new behavior for error types from parse errors

Test Results

✅ All 4 originally failing tests now pass
✅ All 4 new test cases pass
✅ All 491 unsafe tests pass

Fix Pattern

Centralized the check in CheckManagedAddr with refined logic: skip warning only for types that are truly missing (Empty/NotATypeOrNamespace), but still report for other error scenarios (e.g., Inaccessible types). Uses modern C# pattern matching syntax for clean code.

Original prompt

This section details on the original issue you should resolve

<issue_title>Quality of implementation: superfluous errors for pointer to non-existent type</issue_title>
<issue_description>Compile the following program:
class Program
{
    static unsafe void Type(Type *type)
    {
    }
}
Expected

Program.cs(3,29): error CS0246: The type or namespace name 'Type' could not be found (are you missing a using directive or an assembly reference?) [/Users/hugh/Documents/GitHub/repo/repo.csproj]

A single error that we can't find the type

Actual

Program.cs(3,29): error CS0246: The type or namespace name 'Type' could not be found (are you missing a using directive or an assembly reference?) [/Users/hugh/Documents/GitHub/repo/repo.csproj]
Program.cs(3,29): error CS0208: Cannot take the address of, get the size of, or declare a pointer to a managed type ('Type') [/Users/hugh/Documents/GitHub/repo/repo.csproj]

The second error is pointless in this case as the type doesn't exist. I would suggest not checking if we can take the address, size or declare a pointer to a non-existent type</issue_description>

Comments on the Issue (you are @copilot in this section)
@RikkiGibson Currently we refrain from giving the ManagedAddr error (CS0208) for sizeof and stackalloc array creation when the type is an error type. It seems like we don't need to give the error in this case (pointer to an error type) either.

Fixes #38378

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Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

CyrusNajmabadi · 2025-10-16T15:20:24Z

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

+        [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/36877")]
+        public void PointerToNonExistentType_NoSuperfluousError()
+        {
+            var source = @"


@copilot please use raw string literals.

Updated to use raw string literals in commit 7d8a30f.

CyrusNajmabadi · 2025-10-16T15:20:56Z

src/Compilers/CSharp/Portable/Symbols/ConstraintsHelper.cs

+                    var pointedAtType = ((PointerTypeSymbol)type).PointedAtType;
+                    if (!pointedAtType.IsErrorType())
+                    {
+                        Binder.CheckManagedAddr(args.CurrentCompilation, pointedAtType, args.Location, args.Diagnostics);


@copilot would it make more sense to put the IsErrorType check inside CheckManaged address? If not, why not?

Good suggestion! Moved the IsErrorType check into CheckManagedAddr in commit 7d8a30f. This centralizes the fix and automatically handles all call sites, making the code cleaner and more maintainable.

CyrusNajmabadi · 2025-10-16T15:21:38Z

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

+                // (4,31): error CS0246: The type or namespace name 'Type' could not be found (are you missing a using directive or an assembly reference?)
+                //     static unsafe void Method(Type *type)
+                Diagnostic(ErrorCode.ERR_SingleTypeNameNotFound, "Type").WithArguments("Type").WithLocation(4, 31)
+                // Should not also report CS8500 or CS0208 for managed address of non-existent type


@copilot no need for this comment. And the same with the remainder of the tests. The last paren can also be pulled up to the same line that WithLocation(...) is on.

Removed unnecessary comments and improved formatting in commit 7d8a30f.

…raw string literals, remove comments Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

CyrusNajmabadi · 2025-10-16T20:50:15Z

@copilot the following 4 tests are failing, now that that warning is no longer being reported. can you fix them all up:

Microsoft.CodeAnalysis.CSharp.UnitTests.FileModifierParsingTests.TypeNamedFile_03_CSharp11
Microsoft.CodeAnalysis.CSharp.UnitTests.Semantics.DeconstructionTests.PointerTypeInDeconstruction
Microsoft.CodeAnalysis.CSharp.UnitTests.BaseClassTests.CyclePointer_UnsafeContext
Microsoft.CodeAnalysis.CSharp.UnitTests.BaseClassTests.CyclePointer

…ssing types Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

Copilot · 2025-10-16T21:03:46Z

@copilot the following 4 tests are failing, now that that warning is no longer being reported. can you fix them all up:

Microsoft.CodeAnalysis.CSharp.UnitTests.FileModifierParsingTests.TypeNamedFi...

Fixed all 4 tests in commit 5c51e77. Refined the IsErrorType check to only skip the warning for truly missing types (LookupResultKind.Empty or NotATypeOrNamespace), while still reporting it for types that exist but have other issues (e.g., inaccessible types). Updated test expectations for PointerTypeInDeconstruction and TypeNamedFile_03_CSharp11 where error types from parse errors no longer get the warning.

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

CyrusNajmabadi · 2025-10-16T21:06:38Z

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

+            var source = """
+                class Program
+                {
+                    static unsafe void Method(Type *type)


@copilot unlike in C++ in c# we put the asterix next to the type not next to the name. so Type* type. Can you fixup all these tests to follow that style.

Fixed the pointer syntax style to use Type* type instead of Type *type in all 4 test cases in commit b8f9c2a.

Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

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

CyrusNajmabadi · 2025-11-03T16:43:29Z

@dotnet/roslyn-compiler ptal

AlekseyTs · 2025-11-03T17:35:31Z

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

        {
+            // Skip the check for error types that represent truly missing types (not found),
+            // but still report for error types due to other issues (e.g., inaccessibility).
+            if (type is ErrorTypeSymbol { ResultKind: LookupResultKind.Empty or LookupResultKind.NotATypeOrNamespace })


LookupResultKind.Empty or LookupResultKind.NotATypeOrNamespace

Are there tests that observe significance of this condition? I.e. they would fail if the condition was removed. #Closed

Are there tests that observe significance of this condition? I.e. they would fail if the condition was removed.

Still would like to get an answer, pointing to specific test(s)

Added a couple of demonstrative tests in 7242579

AlekseyTs · 2025-11-03T17:36:01Z

Done with review pass (commit 11)

AlekseyTs · 2025-11-07T15:27:47Z

Done with review pass (commit 12)

…uous-pointer-errors

CyrusNajmabadi · 2025-11-12T06:52:59Z

Anything more needed here?

AlekseyTs

LGTM (commit 14)

CyrusNajmabadi · 2025-11-13T08:11:31Z

@RikkiGibson @jjonescz ptal :)

Initial plan

9cad032

Copilot AI assigned Copilot and CyrusNajmabadi Oct 16, 2025

Copilot started work on behalf of CyrusNajmabadi October 16, 2025 14:14 View session

Copilot AI and others added 2 commits October 16, 2025 14:57

Fix superfluous managed address errors for pointer to non-existent type

843fb35

Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

Add comprehensive tests for pointer to non-existent type fix

6ecb4d1

Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix superfluous errors for pointer to non-existent type~~ Fix superfluous managed address errors for pointer to non-existent type Oct 16, 2025

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Address PR feedback: move IsErrorType check to CheckManagedAddr, use …

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Fix failing tests: refine IsErrorType check to only skip for truly mi…

7aa9766

…ssing types Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

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Fix pointer syntax style: use Type* instead of Type *

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Merge branch 'main' into copilot/fix-superfluous-pointer-errors

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Merge remote-tracking branch 'upstream/main' into copilot/fix-superfl…

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…uous-pointer-errors

Add tests

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[Automated] PRs inserted in VS build main-11215.03 #81262

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Fix superfluous managed address errors for pointer to non-existent type #80760

Fix superfluous managed address errors for pointer to non-existent type #80760

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Summary

Changes Made

Test Results

Fix Pattern

Expected

Actual

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